Racing Fuel Systems

Hello guys this is a first post here and please bear with me as this is a long post and drawn out problem that I can't get figured out and I am having a very difficult time trying to get a Holley 600 Vacuum secondary carburetor to work on my build. My engine is a 350 Dart SHP 350 small block chevy, Edelbrock Performer rpm dual plane intake. Dart 200cc pro 1 platinum aluminum heads with 9:1 compression. I have a 268/272 220/224@50 510/510 lift 110 intake center line/114 lobe separation angle custom hydraulic roller camshaft. Ignition system is an aftermarket large cap HEI distributor with 16 degrees initial timing plus 12 degrees of vacuum advance added at idle for a total of about 28 degrees of timing. My timing is all in with about 36 degrees at 3000 rpm.

On my engine it was a brand new build and since day one nothing I have put on this engine is working for carburetor wise. This problem started on my previous build in which I had a Dart 377 SHP De stroked build before this 350 build and it was a 4.155 bore x 3.48 stroke with all the same parts above with the whole same top end and the camshaft minus the intake being an Performer air gap rpm intake. I wanted to change and go a bit lower on my build so I swapped out the Dart 377 short block with my Dart 350 short block and used the exact same top end from my 377 and the camshaft from that build. On the previous 377 build I started off with a Edelbrock victor jr intake and had a slightly bigger camshaft 276/280 228/232@50 510/510 lift 106/112 lobe separation angle and was a custom grind hydraulic roller cam. It ran fine and no problems getting a carb to tune on it.

After I swapped out the camshaft to the slightly smaller grind and over to an Edelbrock Performer rpm air gap intake I had problems with that engine.

That engine ran fine but after I swapped out only the camshaft and the intake from the victor jr intake to the performer rpm air gap I had problems with whatever carb I stuck on the previous 377 eventually fouling out my spark plugs over a short period of time and I was burning correct heat range plugs. This is in a truck that I drive on only the occasion and I have not been able to put much miles on that previous motor for several reasons which I won't post here.

I had before the cam swap a Holley HP 750 double pumper and also a 650 double pumper and they tuned fine and easy with the bigger cam and victor jr intake. After I swapped out the intake and the cam to the smaller camshaft listed above it has never ran right since day one and no matter what adjustments I use on my carb of choice I could not get it to work very well and in short order the plugs were getting fouled out.

I used a Holley 600 vacuum secondary on it after the change as I sold my double pumper carbs to have funds for my 350 short block in the works. I have over ten plus years tuning Holley style carburetors and have modified my own metering blocks to take brass allen restrictors so I know my way around tuning the idle circuit on a Holle style carburetor quite well and even put together a custom built double pumper for a guy for his Ford mustang going by his specs so I know my way around tuning these carbs. I only got a brief time working on the 377 but I knew my 350 would be getting together once I pulled the 377 out of my truck to swap out the short blocks with one another.

I had problems with the previous 377 starting off with the 600 Holley vacuum secondary that I had worked on. I started off with .070 primary idle air bleeds and .040 secondary idle air bleeds and I had added a secondary metering block to make it a 4150 and I drilled and taped the metering blocks to take 6-32 brass allen set screws and started out with .033/.033 idle feed restrictor size as a two corner idle setup. It would idle 800 rpm and would be fine for a short time but over time on the 377 it would slowly foul my plugs out and they were getting sooty. The 377 with the new cam had a steady vacuum of 18 inches.

I had checked everything on the ignition and its all pretty much new and the coil and distributor checked out good and also the control module and everything on compression tests were good across the board and valve lash was all checked and verified and also TDC marking on my ATI balancer. The carb showed signs of being too rich so I decreased my idle feed restrictors a slight bit at a time to try and clean up things and ended up putting in a set of new plugs. I run a billet Holley regulator set up at 5.5 psi so fuel pressure is good and the float levels were good.

Long story short I kept having the problem if the plugs eventually fouling out after a while.I ran NGK FR4 and also Autolite 3926 spark plugs. On the carb I had proper transfer slot exposure of no more then .020 and the secondary side opened up enough to allow air to keep the primary throttles in check. I had some adjustment on my idle mixture screws and got the best idle I could. This cam swap with the intake had been so picky with the slightest change since day one and I ended up leaning out my idle air bleeds to .074 primary and .044 secondary.I wanted more time to try and tune it better and at the end before taking the engine out I had .031 primary and .033 secondary idle feed restrictors in the metering blocks on the carb.

I gave up on trying to work more out since I was pulling the 377 out to replace with the top end and the camshaft from the 377 over to my 350 build. Ok here is my current problem as I took the whole top end from the 377 over to my Dart 350 short block along with the camshaft and stuff it had the same problem carried over some how but even worse. My father and me both put it together and he has over 50 years of putting engines together from performance and used to build race cars on the side back in the late 70's through the late 90's with late model dirt track cars and daily driver stuff so he knows his way around stuff quite well and worked in a machine shop and built stuff like this all the time.

To try and keep it short as beast as I can the Dart heads were all checked over on all the valves and the guides were in excellent shape and good valve seal wear margin on all valve seats and the seals were still good and put new springs that work with hydraulic roller cams. The 377 only had about 500 miles on it and those heads were brand new and very little mileage going over to my 350. The camshaft is a billet grind from Mike Jones so it was made by a good camshaft grinder going from my specs I gave him. Everything was blue printed on this engine and all the machine work on the block and rotating assembly was done by a machine shop that builds high dollar racing motors versus just regular type motors like some machine shops do.

Everything checked out on the clearances such as ring gap and bearings and also piston to valve clearances and everything else that is critical to a successful build. Ok on day one that I had the engine done and put into my truck I took my carb and only changed out the idle feed restrictors in the rear to .031 and kept the front at .031. Same .074 primary .044 secondary idle air bleeds. I had this Holley 600 vacuum secondary setup as from previous 350 builds I have had in my truck over the years I kept notes on the entire build on what I had the carb setup with such as all the specs from air bleed sizes to idle restrictor size and also throttle setting and idle mixture screw settings and have a library of notes that I keep for every build and carb tune I have ever done over nearly 15 years and have done at least twenty plus Holley carb builds for my trucks over the years and have over at least 15 different small block chevy builds I have tuned with so I know quite a bit of knowledge and experience on trouble shooting.

On day one I had nothing but the rich condition from the 377 pass over to my 350 build and its even worse. I only got to drive it home last fall for about a 12 mile trip and I could tell it was running super fat rich and thought it was odd to be doing this as the carb should have been very close within a short range of the idle circuit being correct for what my build would need by going by my previous experience with tunign on 350 builds with camshaft specs very similar to this one currently in my engine.

I had put brand new plugs in the truck when the 350 was put in and within the 12 miles they were starting to get really black staring with the number one and two cylinders and would get leaner as it got back towards the rear cylinders. I normally use a one inch 4 hole spacer on all of my builds as it has given me more throttle response over the years but I was never able to use it on the previous 377 after the carb swap since with the cam and intake swap it just would only run rich and slowly foul plugs no matter what I did and had to go to an open one inch spacer to help for the signal to be able to be leaned out enough to drive my truck until I could try and get it tuned.

On my 350 when I drove it home I had issues only on the idle circuit and driving down the highway while being on the mains at 55 mph and 2500 steady rpm the truck ran fine with out any issues such as to much jetting which was at 65 primary and 73 secondary. I had my idle mixture screws out at 1 1/4 of a turn. I only drove it through town for about a 4 mile add up and then parked it at my home in the the fall and it sat for two months as I had to replace my mechanical fan and a pulley and had to fix some lines and pull my radiator for some leaks and had to fix my shroud as my fan picked up something and dinged it up. So I did not have much time to try and be able to tune the carb.

So I finally got my truck up and running again in December of last year and I put in another set of spark plugs as the ones in only just 16 miles were fouled out mostly the front two plugs were totally black while the rest got lesser going back to the last rear cylinders. Basically no matter how I adjusted my carb with .074/.044 idle air bleeds and .031/.031 idle feed restrictors in my metering blocks I could never get it to lean out period. I could take the primary idle all the way off and leave the idle mixture screws out just 1 turn and it would still idle though not good and I could tell it was just running horrible and pig rich. I had a problem that while driving it would studder aka shake at certain throttle positions and when I left off the gas once the throttle plates closed completely it would studder for about a second and a half then smooth out without touching anything. I had the secondary butterflies open up a 1/4 of a turn. I only got 15 inches of vacuum and should have gotten about 18 like this camshaft gave me in my 377.

So I took the carb off and could not understand why it would be this rich. I took the power valve and checked it with my power valve checking tool and it was good and held steady vacuum at its rated 6.5 psi. I checked the main body for warpage and the base plate for straightness and it was really good and less then .03 on the main body and .001 or so on the base plate and I rebuilt the carb before I stuck it on. I know right off hand this carb should not be so fat rich like this as I had a previous 350 in my truck that I ran a 600 Holley vacuum secondar on it and it was very close with 350 cubic inches but with Dart shp 180cc aluminum heads and a weiand speed warrior intake dual plane with a 270/278 219/227@50 515/530 lift 106/112 lunati voodoo hydraulic roller cam with 9:1 compression and held 17 inches of vacuum and same timing specs as I use on this engine.

I ran the 600 Holley with a one inch 4 hole spacer and speced the carb at .078/.048 idle air bleeds and .031/.031 idle feed restrictors in the metering blocks 65/73 jetting and had a 800 rpm idle and it would allow me plenty of adjustment of my idle mixture screws and nice clean burning plugs using NGK FR4 or Autolite 3926. I had 17 inches of vacuum with that cam since it had 50 degrees of overlap versus my current cam having only 42 degrees. So I know I should be close to at least be able to adjust my idle mixture screws and able to kill my engine.

I took the carb off and went through it and to rule it out I have several Holley vacuum secondary 600 carburetors at the side for spares and are like new condition and even rebuilt the baste plates on some and got brand new metering blocks on them. I wanted to try and use my four hole spacer again and see how it would work and in all times past putting a four hole spacer one inch always gave my carb more signal and more throttle response and never any problems. Using an open spacer only took away some bottom end and gave more at the top which is what they are designed for as I have used both in may different applications.

I took my carb off and then put another 600 vacuum holley secondary on it but kept the same metering blocks that I customized to change out the brass allen set screws and I leaned out the front from .031 down to .028 which is the stock size normally for this carb. I left the rear at .031 which is also stock for this carb out of the box on there metering plate that it normally comes with. I have Holley's secondary metering block upgrade that is for this carb. I then put another 600 vacuum Holley on it and I had the stock setup of the idle air bleeds at .078 primary and .048 secondary and the .028 primary idle restrictor and .031 idle restrictor and I put my four spacer on to see how it would react.

It ran just so much more rich that I could hardly get it to idle even decent and only could get 15 inches of vacuum it was running so rich and I had blue smoke coming out the tail pipes and I adjusted the idle so i only had .020 or less throttle opening on the transfer slot so it was not over exposed and the secondary still at a 1/4 open. No matter of adjustment would allow me to get any response from my idle mixture screws and I could turn the driver side in all the way and the engine could still run and then I could leave the passenger side open 1 turn on the mixture screw and back my main idle screw all the way off and my engine would still run. No fuel coming out the boosters and no flooding going on and float levels always been verified time and time again.

I took it for a small drive though town and with the four hole spacer on it would just feel so soggy from being overly rich it would not run very strong and clean no matter what I did and never in my life in 15 plus years messing with a Holley carb have I had this problem. I would expect this with a very large camshaft with a massive amount of overlap and low vacuum but I have tuned with cams like that before without problems with just a tiny bit of time.

In a previous other truck I owned I had a 350 with a Holley 650 double pumper and I ran a comp cams big mother thumper hydraulic roller cam and tuned the carb in just a few hours with minor changes and no problems using my experience and knowledge and got a good clean idle for what can be done with that big of a cam and it only had 6 inches of vacuum in park and yet I could tune to work with that.

I after just a four mile drive just in town my front two plugs were totally black and get lesser black towards the rear. Basically it looked to be some weird fuel distribution problem as it would get really super rich in the front two cylinders and then slightly less richer in the number 2 and 4 cylinders and then leaner yet in the 4 and 6 cylinders and really leaner in the 6 and 8 cylinders as far as how the plugs looked. I took out the plugs and put in a new set again and then took off the carb and once again looked it over and all was good.

I thought maybe the air gap intake was giving me some sort of fuel distribution problems as it showed up in my plugs as when cylinder one fired it would be rich on that plug but compared to cylinder number 8 spark plug it was the complete opposite and hardly any color on the plug. The when cylinder 7 fired it was way leaner and hardly any color on the plug but cylinder 2 would be pig rich. Same with the others. So to rule out things I changed the air gap intake out and put on a non air gap Edelbrock rpm performer

I then took a brand new 600 Holley vacuum secondary that I had at the side and used its front metering block with its pressed in factory .028 primary idle feed restrictor and I checked the power valve and it was good and tight and the gasket was good. I then used my secondary metering block only from the previous 600 vacuum secondary. These are all either an 1850 model manual choke or a 80457 electric choke but I have used only a manual choke on all of them.

I know its running really rich as in the cold weather here in Ohio and only 25 degrees outside I can start it up with no choke needed and in the past with the previous 350 build I once had before the 377 I had to use a choke to get it fired up. I this time put my one inch open spacer back on as it leans out my carb signal enough to allow me some better driving manors slightly and with no blue smoke coming out my tail pipes. After putting this 600 Holley 1850 on with stock out of box air bleed sizes of .078 primary and .048 secondary and .028 primary idle feed restrictor and .031 secondary idle restrictor I set up my primary idle to show a square transfer slot of less then .020 and then opened up my secondary this time to half a turn open to allow more air in. I then hooked up my vacuum gauge and setting my primary idle mixture screws at 1 1/4 turn out I got 17 inches of vacuum this time.

I tried to adjust the mixture screws to get any change and once again I could not get it to kill the engine even with both sides going in all the way on the idle mixture screws. I then adjusted the idle mixture screws and now at least I was getting some slight changes unlike before but not enough to have any true adjustment ragne that this carb should be giving. I went through several changes and adjustments and I could stil turn the idle mixture screws in on both sides and still not kill the engine. With the open spacer back on I had a healthier cleaner snap of the throttle comapred with the four hole spacer which is not normal for this situation when things are working right like they should in normal situations.

I adjusted my idle to 800 rpm as it would never idle less then this with any of my previous builds with a cam of this size and it drops to 700 to 600 in gear. I before the intake swap to the performer RPM non air gap intake was not able to kill my engine. I had my idle set at 800 rpm and according to my notes on my adjustment my transfer slot was no longer showing and was just below where if you gave the primary idle screw a 1/4 of a turn more it would just start to show the transfer slot. I left my idle mixture screws out at 1 turn. If I turned my idle mixture screws in my engine would still not kill but the vacuum reading now finally would lower some but not much change though. If I backed my idle mixture screws back out at half a turn and backed my idle screw all the way off it would still not kill the engine.

Now finally I was able to get my engine to kill by turning the idle mixture screws all the way in and if I backed my primary idle screw off all the way and that is the first time getting that. I then put my idle primary idle back to 800 rpm which is without the primary transfer slot showing and just before it would start to show and the secondary open up half a turn. If I had my idle mixture screws out at only a 1/4 of a turn it would hardly run while in gear with my automatic turbo 350 transmission which I have a 2200 plus stall convertor with it and 3.42 rear gearing. I was never able to get it to kill before in gear even with the mixture screws all the way in on both sides but now it would do so.

I was able to put them half a turn out and it would at least allow me to drive it. In park it studders and you can tell its still too rich but once you drop it in to gear it smooths out. While driving in town it now drives smooth for the most part but I still get a studder once I let off the throttle and the blades snap close it will studder for abouta second and half and then smooth out without me touching the throttle.

The reason I am putting this long post is this carb should be giving me a good range of adjustment with this cam as my brother owned a 1988 chevy caprice over ten years ago and he had a bone stock 305 engine in that thing and he had a Qjet that went bad and I got him a Holley 600 vacuum secondary carburetor used for him and it was stock settings from the factory. They were . 078 idle air bleed primary and .048 secondary and the .028 idle restrictor primary metering block and .031 restrictor in the secondary metering plate number 9 it comes with and it ran fine and adjusted no problem on that old motor.

I know my stuff enough and with a previous 350 build with 9:1 compression and a lunati voodoo hydraulic roller cam which was a 262/270 211/219@50 500/515 lift 106/112 lobe separation angle and 19 inches of vacuum and 200cc heads and a dual plane intake edelbrock rpm performer, I had a 600 Holley tuned on it with my four hole one inch spacer and ran the same air bleed combo and the idle feed restricor size was .031 front and .031 rear with the secondary plate being replaced with the metering block and it allowed me a 800 rpm idle and proper transfer slot exposure with the secondary side being open up similar to what I got now and I had my idle mixture screws out at 1 1/4 of a turn.

According to my notes on that build and in my experience with anything less by turning my driver side scew in less then one turn the engine would studder and shake real bad and eventually die out so I knew it was good and adjustable and tuned well and the plugs were good and tan. I apologize for the long post as I just want to get as much in formation down here. I wanted to know why this mystery issue is going on and I have verified timing with two different timing lights and verified TDC when the engine was put together. I havve done a compression check and all cylinders give around 170 psi.

The heads were re checked over with a fine tooth comb and all was good on the valve guides and seals. The lifters are Morel hydraulic roller lifters which are over the $800 price point with the .750 sized roller wheels and nothing has been cheap in this build. I looked over the 600 Holley and the carb body is brand enw along with the metering block on the front and rear was bought new separate from the main body. The only thing is the base plate is a older model were the pcv port is on the passenger side going straight into the base plate versus on most vacuum secondary Holley carbs made after 2010 the pvc port is in the rear of the base plate.

So I got to wondering why is it I have to get one full turn on the primary idle mixture screw to just get below the transfer slot before it shows up. I then have to get one and a half turns on the idle screw to get a .020 transfer slot exposure using my feeler gauge to get that size. I then remember on my previous newer 600 Holley vacuum secondary carbs that I used previously for other folks and on my previous 350 build before my 377 I only had to go 3/4 of a turn to show a .020 transfer slot exposure. I then took a dial caliper and found out that on the older Holley base plates on the vacuum secondary carbs with the pcv port on the side the transfer slot sits .380 or a slight bit higher up from the bottom of the bast plate. On the newer design vacuum secondary base plate used since around 2010 and later till now the transfer slot sits up only around .360 up from the bottom of the base plate and is longer then the older base plate.

This is the only thing I can find different so far compared from a slightly older Holley 1850-5 with the pcv port on the side of the base plate versus on a more newer 1850-14. I had also ran a Holley 670 Street avenger on previous builds and it had the pcv port in the back and I only had to open it up about 3/4 of a turn to only half a turn to get my idle along with a 1/4 to half on the secondary adjustment and about 1 1/4 to 1 1/2 turn on the idle mixture screws.

Now on my truck once again from previous builds. In 2009 I had a 350 with World product 200cc heads with an Edelbrock Performer RPM intake and 9:1 compression with a Crane Hydraulic roller camshaft with 283/291 222/230@50 515/520 lift 108/112 lobe separation angle and 16 inches of vacuum and I was able to run a 600 Holley vacuum secondary with the stock air bleeds at .078/.048 and a .034 primary idle feed restrictor and a .031 idle feed restrictor and a 900 rpm idle with proper transfer slot exposure and a good running build with using my four hole spacer and clean fast snappy running engine. That cam had 60 degress of overlap and this current cam in this build only has 42 degrees with way less overlap and should not be running this rich with this carb setup with my current specs and no matter what I do I so far can't get anything to hardly budge on it.

Can anyone maybe have any ides on what else yet to do? I have another 600 Holley I am going to try and it has the newer base plate with the longer transfer slot and see if that is the problem being on the older one I have too turn the primary idle up so far that even though its not showing the transfer slot yet it could be in theory allowing enough air to be pulling from the transfer slot anyway thus causing the rich idle and not allowing me to adjust my idle mixture screws as that is the normal symptom when you have to much transfer slot exposure.

The slot sits up so high that when you get about .020 transfer slot exposure on the passenger side you can see the bottom of the timed port hole in the base plate that feeds the timed port on the metering block. You can't get that with the newer base plates as the .020 transfer slot showing still does not show any of the timed port hole. I hope anyone out there can help me cuse I am at my wits end and after three different carbs on this thing I am ready to pull my hair out and I have never dealt with an issue like this and I know my way around on checking the basics and advanced area to know what I am doing and this has thrown a curve ball at me that I can't seem to figure out.

Sorry for the long post but I want to share as much as I can so maybe someone can get enough information from what I posted and maybe have came across a similar issue and can help me out with some ideas as I am out of them. I appreciate any help and thanks for anyone who reads.

Also to add to this I once again checked spark and I have a nice blue spark so I know the coil is putting out a good spark and I tested the resistance on all my plug wires and they are as good as they was new and the wires are not cheap ones. They still look as good as new and are less then two yeas old. I checked by spraying the wires with a water spray bottle and looked under darkness and saw no sparks arching anywhere and the cap looks good inside and everything making good contact with the rotor and the distributor looks like new still and the weights move freely. There is no vacuum leaks and have plugged all that stuff off and checked everything there is possible and that needed to be checked ignition wise and electrical and mechanical.

I got a call from a mate of mine that has Pontiacs, he & his brother. One has 455 power, the other 400. On a recent trip, the 455 got 22mpg, 23 mpg for the 400. [ these are Imperial gallons ].
They did NOT have Holley carbs. They had Carter TQs that I modified.
You seem to know your carbs & how to tune them. However, something ain't right. I would try a Carter/Edel AFB. It is a better design than brand H [ and clones ], more reliable & better throttle response all else being equal.

I know you have come here looking for carb tuning advice but I don’t think that’s your problem. Forgive me if I haven’t read through all 42 paragraphs but it was the first paragraph and first sentence of the second that held your answers. Your attempting to tune a carburetor that Holley intended on an engine with a whole lot smaller manifold, head cc’s and camshaft, most likely exhaust too. It may not be an impossible task but as you have demonstrated a very difficult one. 9.0:1 compression along with the aforementioned build specs sends off alarm bells as dynamic compression would be low and I bet volumetric efficiency too. Ignition advance is not enough to artificially build cylinder pressure starting with such little static compression and the cam you have. You may well also find that 12* of vac advance reduces a fair bit with a lot of your driving other than steady cruising. Locking your distributor timing may help.

By default the 377ci would have had more compression and a little overlap to help with incoming intake charge. With both cams having the intake close at the same ABDC* compression wise your losing too much with the smaller cam and all but no overlap to help with intake charge. So I can see why the 377ci didn’t give as many issues.

To get to the crux of the problem, what your seeing with the black, fouled plugs may well be poor combustion events with a mismatched build that is not promoting a well atomized, homogeneous mix that is not vaporizing as much as it can before and during combustion. The best way to tune that carburetor could be to use those 200cc Platinum Pro 1’s to fund some 175cc - 180cc intake heads with a 62cc - 64cc chamber. Build some compression and intake velocity. Don’t confuse high vacuum with high velocity.

I agree with Right hand drive. I read that whole thing and wish I had not.
Don't know what model 600 cfm carb you are working with in your novel. But I can tell you this 1850-2 and -3 600cfm carbs have .027" IFR not .033"

Thank you guys for the replies and appreciate your time and your comments but I have used a 600 Holley style carb from stock builds to wilder and even 350 builds with bigger camshafts then this build has and never had a problem getting it worked out and working well.

Ok for one I know a Holley 600 vacuum secondary model 1850 manual choke carb or the 80457 electric choke model carbs don't come with .033 idle feed restrictors in them but I don't know how much you know but changing the idle feed restrictors in a Holley carburetor is how you either make the idle transition circuit either richer or leaner depending on what your build requires. The same thing with the idle air bleeds.

Most folks don't know how to tune the idle circuit on a Holley style carb if needed and sometimes end up putting it on build and without it being calibrated right, it can end up not running well. For example a 600 Quick fuel slayer vacuum secondary carb is calibrated way richer on the idle circuit then a Holley 600 Vacuum secondary out of the box. A Quick Fuel slayer 600 comes with a .031 or a .033 on the primary idle feed restrictor on the primary side and a .039 idle feed restrictor on the secondary metering plate. A 600 Holley vacuum secondary normally comes with a leaner calibration of a .028 primary idle feed restrictor and a .031 idle feed restrictor in the secondary metering plate. Holley does change slight things at times so it can vary by a hair. If you were to throw the Quick fuel carb on a very mild build with a nearly stock camshaft on a small block chevy it would be pig rich compared to the Holley.



That is what I am talking about on changing the idle feed restrictors out along wit the air bleeds as that is advance tuning that many people don't touch on there Holley style carbs and if you don't know what I am talking about or putting down then please don't trash me for it as I am just trying to be informative about what I do know on tuning.

There is more to tuning a Holley carb then just taking it out of the box and throwing it on and adjusting the idle mixture screws and changing jets like most average tuners do and don't know advance tuning on these things. That is why on some of the Quick fuel carbs you can change out the idle feed restrictors in the metering blocks and on some models you can even change out the emulsion port size to calibrate things even more.

Sorry if I sound rude and I am not trying to come off like that as I am just putting down that there is other areas you can tune on these carbs that most of the average tuner does not learn or know to do so that can either make it run even better or not at all and be able to give whatever build you got what it wants from the carb you stick on it if its a Holley style.

I have used a 600 Holley on many builds over the last twenty plus years from mild to wild and the last ten years in general and I have been able to always have then tuned to whatever camshaft I have used in my build. Yes the compression in on the slight lower side compared with the former 377 but I have had several previous builds with similar setups and similar cams very similar in size and had no problems using either a 600 or 650 Holley carb regardless of it being a vacuum secondary or a double pumper and got them calibrated no problem.

This is one time that a problem has come up that has caught me off guard here. I am sorry that you had to read so much but how else am I going to get what all I have been through so you see how much I have exhausted everything else on checking things and to have perhaps anybody else who may read it that may have come across an issue like this before and be able to give some advice if they had a very similar problem. Sorry for the long read but if a person does not put enough information down then they get the help they need but sorry for so much but I did not want to leave any details out so I don't get a request to check this or that that as to where it already has been done.

I have done enough on these carbs over the years to calibrate them to what my engines needed and ran excellent without an problems but this is a first for something to come up like this while checking all other things and not coming up with an answer on what my problem is that is makign it like this. Previous very similar builds with same compression and camshaft size I never had any problems even with bigger shafts and more overlap and less vacuum at idle.

Thanks GTO for being nice about things and appreciate your comments and advice. Those builds sound pretty cool. I have used Edelbrock carbs in the past and tuned them quite well and have used them on several builds over the years and I have seen the recent Edelbrock AVS 2 carbs that they put annular boosters on which gives a way better signal versus the older style straight leg boosters that they used to use on the older AVS carbs and I know the Edelbrock Performer carbs are nice as well and can work good on builds but I get better overall performance with a Holley style versus the Edelbrock but that is just my preference but I have gotten over 19 mpg on my small block chevy builds even with way bigger camshafts then what I have currently in my 350 build and that is pretty good with the setups I have had concerning my wife's vehicle which is fuel injected only gets 19 mpg on the highway.

I tuned an Edelbrock 600 performer once for a guy who owned a nice built 350 with a comp cam 292h hydraulic flat tappet camshaft with 244/244@50 duration and 501/501 lift and I told him the carb was a bit small for his radical build but it was what he wanted and liked on his engine and I tuned it up for him and he loved it and it was in a 1980 Chevy Camaro.

I have spent many years of reading and learning on tuning carburetors and spent a lot of time helping others on tuning issues on another forum and have helped many get there carbs dialed in quite well and even built one from scratch for a guy who had a carb that was running horrible on his build and all I asked for was his specs such as his cam size and setup and other factors and put together a 650 double pumper Holley for his Ford 351 Windsor that had a very radical solid roller camshaft in it and I put it in a ball park figure to start off with and he knows nothing about carbs but my Father put it on his build and adjusted things and it was pretty spot on and the guy loved it.

He no longer had an over rich idle along with no more stumbles and it cleaned up his plugs really well and even picked up some mileage to boot and he loved it and his engine ran very strong and healthy. If I did not know what I was doing then I would have not known how to help him out. His carb he did have was from a swap meet and was messed with and was so bad it was a lost cause trying to even attempt to fix it was an older style Demon carburetor before Holley bought Barry Grant out and the metering blocks in it were slightly different then the traditional Holley design and the main body as well so I could not fix what they had done to it whoever owned it before him.

I don't believe it s a carb issue as to me something else is just off somewhere but trying to find out what it could be is the problem. My compression difference between my former 377 build and this 350 build is less then one point difference.

I don't know where in those 42 ? paragraphs where it says your current configuration and carb model

Ok I am using a 600 Holley vacuum secondary model 1850 with a manual choke and its a square bore carburetor. I have a secondary metering block upgrade in the rear in place of the metering plate. I have it jetted 65 primary and 72 or 73 secondary as I don't have my notes in front of me. Am using a 6.5 power valve. I have modified my metering blocks to where I can change the idle feed restrictor size to what ever I need to calibrate the idle circuit on it like you can do with billet metering blocks or cast metering blocks like Quick fuel makes to advance tune it which on standard Holley carbs they don't give you that feature.

I used this size and model carburetor over the last ten plus years on at least 5 different 350 builds with either smaller or slightly bigger camshafts and only had to do some minor changes on the idle circuit by not much and it always allowed me to have good adjustment on the mixture screws and ran fine. Example previous build I once had a 350 small block 9:1 compression with 200cc RHS cast iron heads with an Edelbrock performer rpm intake and a Lunati voodoo hydraulic roller cam 270/278 219/227@50 515/530 lift 106/112 lobe separation angle.

I ran a 600 Holley vacuum secondary model 1850 like I listed above and I replaced the secondary metering plate with a metering block that goes with that carb from Holley and I had it jetted near identical and out of the box the idle circuit was slightly to lean and I had to change the idle feed restrictor in the front from stock size .028 to .031 and then it was spot on for said build. I only put that information down just to show I have ran very near identical combos before and never an issue like I am having right now.

I write down my adjustments on my carburetor and the proper range I can move my primary throttle so my transfer slot is not over exposed past being square or to much more then .020 being exposed. I also mark down any adjustments I make and put down my final settings. I have kept tuning notes from all of my builds over the last ten plus years and what my carburetors were all set at from jetting to the idle air bleeds and also the restrictor sizes in the metering blocks along with carburetor settings on the idle mixture screws and my primary idle screw setting. Also jot down shooter size and the pump cam being used and number position used as well on all of my notes in great detail.

Again a simple list, no comments