Racing Fuel Systems

Re: Holley 600 Vacuum secondary tuning issue.

2022-02-18T00:10:09+01:00

Bad Camaro where did you get that guitar string as I would love to do that with mine. I did finally find out the problem and it was the base plate the whole dam time and never would have thought that it would have been the issue. I got to thinking and put my cards down on the table as a figure of speech and got to thinking what was different in the previous 600 Holley carbs I used and a 670 street avenger and the base plates were the only things different then the older design base plates being the difference on the carbs I used. The three different ones I used all were done with the older design base plate and I measured the transfer slots and the primary side was about near .400 from the bottom of the base plate and the newer design ones that Holley has used now for ten plus years the transfer slot is only about .360 from the bottom from the best I can measure.

Then on the secondary side the transfer slots are longer on the older design and the newer design they are a lot shorter but I can't say by how much as I don't have my note book out. Bottom line installed my new 600 Holley on today and got all my pre adjustments done and started it up and wow it started up a bit sluggish at first but its normal before you get the proper settings and stuff. After a few adjustments and looking at my vacuum gauge and it got up to temperature the engine sounded so healthy now and the carb adjusted like it should have done with the last one. I had my primary transfer slot open up about .015 and my secondary side open up half a turn and my idle mixture screws would all adjust excellent just like it normally should have been before but that older base plate for some reason with the such shorter transfer slot did not allow for a proper butterfly adjustment and even if I did not have the transfer slot exposed the opening would still just be too much.

It was not warped as I used a straight edge and I could drag a .001 feeler gauge at all angles and it was like new condition. Like I stated I have worked on these things for so long I knew it had to be something out of the ordinary that would be the issue. I am glad it was not a camshaft grind issue as I was just trying to figure out the culprit as this was one of the curve balls that can come ones way. After comparing the carbs and then noticing the needing 1 and a half turns on the older style base plate versus the only 3/4 of a turn needed on the newer base plates, I knew that would have somehow have a big effect on idle and other factors.

Bottom line I would hate to throw them away since I could never use it at least on my build if I ever needed it. if I could make them longer that would fix it. What got me to thinking about that is because of the history of the Quick fuel carbs having to long and to wide transfer slots compared to the old design Holley carbs and the troubles it caused folks in some instances and that is where I figured I would try that theory and bam I was correct and it fixed my problem completely and the idle is not smooth and the throttle is snappy and no popping and the engine runs good in idle and in park again like it should have. Now just to get it out and do the finer tuning and then enjoy it finally after all this time of a year battling this thing and it was that one little thing that caused the biggest problem.

Cases solved.

Statistics: Posted by eric76 — Fri Feb 18, 2022 12:10 am

Re: Holley 600 Vacuum secondary tuning issue.

2022-02-17T03:21:29+01:00

What I have done with those 750 base plates that have the shorter transfer slots on the sec side is to take my little guitar saw I have and make them the same length as the pri side. Did that on my old 4779 750 and it worked out great with getting both side balanced the same. It ran pretty good last year at the track for a 30 year old carburetor.

Statistics: Posted by 80Camaro — Thu Feb 17, 2022 3:21 am

Re: Holley 600 Vacuum secondary tuning issue.

2022-02-16T15:34:41+01:00

I have another 600 Holley that I am putting on today and see how it goes. I have done the same thing with another 600 Holley vacuum secondary. I took the main body and grinded the clearance needed for the bigger 1 11/16 base plate. I then popped out the straight leg boosters and installed stepped down leg boosters and then put a set of center hung fuel bowls on and then a Quick fuel adjustable pod to really tune the secondary side of things to get the best opening rate.

That carb is apart for the moment as is a long story on that one. It started with my current problem that went from my previous build over to the current build and I did some investigating on things and the previous Holley 600's I used in the past had the older base plate where the PCV port was on the side and not in the rear like the newer ones have been for at least ten plus years. The old 600 Holley 1850's I used along with the Holley 670 Street avengers were all the newer style base plate and I wondered what is so different that I never had problems with the newer style 600 carb design versus the older ones.

The base plates are not just difference in the design but also the length of the transfer slots changed. On the older side port PCV or brake booster what ever you would want to hook up to that port, base plate design I would have to do 1 and a half turns on the primary idle speed screw to just get just hardly a square transfer slot of about .015 as a .020 feeler gauge would cover it out.

On the newer design base plate with the 3/8 tube in the rear it on all of them takes me only 3/4 of a turn to get a square .020 transfer slot. I got my dial caliber out and measuerd the transfer slots both front and rear comparing on both base plates and the older ones have the transfer slot almost .380 to .400 up from the bottom of the base plate and is way shorter which would cause some problems in theory at least on my build. The newer ones are only about .360 from the bottom at the most and that .020 to .040 difference in transfer slot on the newer and older base plates would effect a lot of thigns in certain situations as that transfer slot is very critical in more ways then one.

I also found out on the older base plates the secondary transfer slot is a lot closer towards the bottom and longer versus the newer ones being further up. I don't have my measurements on that one but the old base plate has been the only thing that has been on the past 1850 models I used and I am putting on a brand new 600 vacuum secondary that has the current base plate design and I am going to find out if the transfer slot difference being the biggest change and difference and me having to open up the old base plate so much to get my idle speed has been part of my problem the whole time.

In the past my old builds were always used with the newer design plates. Its most likely just a shot in the dark but I know a lot of folks who use Quick fuel carbs have problems with there builds at times as there transfer slots are a lot longer and wider and contribute to a lot of issues in certain builds. This might be a case to where the transfer slot on the older base plate is just to short to work with my particular setup and is causing the problems with the idle mixture screws not working. Nice work on your carb by the way and looks good.

Statistics: Posted by eric76 — Wed Feb 16, 2022 3:34 pm

Re: Holley 600 Vacuum secondary tuning issue.

2022-02-13T02:22:13+01:00

I know I am new here, but I had to reply to this 600 Holley thread as the 1850 gets little respect in the carburetor world. About 5 years ago I had the same problems with my 1850's I used and I remembered one that I build for a 454 I ran in my car in the early 90's. Now even though the 454 was only good until around 5500rpm with it that little 600 1850 would get there much quicker down the track than my 3310's did. After that I decided a few years ago to make a tricked out one. I took the air horn off (not sure if it helped), got rid of the sec metering plate for a new rear block to change jetting there, but the biggest change was when I adapted the 3310 baseplate to the 1850. I did use a die grinder by hand and opened up all the bores to match the bigger baseplate stuck it on the main body and started out the jetting at 69 Pri and 76 Sec. pretty close to what a 4776 600dp was. My 1st runs with it were in the mid to high 11's and I was like WOW this carburetor works. I t was so good that day the smallish 600 was within .003 of my 750 well tuned Mighty Demon and the 60ft. and 1/8 mile times were a few hundredths better. The 600 had such a good signal to the booster that when you cracked the throttle it would literally pull the sec side open so I did need to slow it down a little. All my HSAB and IAB are stock 1850-1 specs with stock metering blocks also. I highly recommend doing the larger 750 baseplate on a 600 like this as it works very well. Guys at the track that day told me, no way is that a 600 Holley running that fast. I told them to measure the throttle openings by the boosters, a lot of, how in the h**l can that work.

You guys have a great fuel site here, I should have joined sooner. Thanks for letting me join.

Statistics: Posted by 80Camaro — Sun Feb 13, 2022 2:22 am

Re: Holley 600 Vacuum secondary tuning issue.

2022-02-07T15:15:53+01:00

I coped and used your list and changed to what mine is.
Holley 1850-14

Main jet #65
Primary metering block Stock out of box and current
PVRC .045 to .048 "
IFR .028"
Emulsion .028"
Emulsion .028"

Secondary Metering block upgrade from Holley matched to this carb
IFR .031"
Main jet .073"
Emulsion .028
Emulsion .028

Main Body stock as it came out of box no changes
Prim IAB .078"
Prim HSAB .025"
Sec IAB .048"
Sec HSAB .025"

Statistics: Posted by eric76 — Mon Feb 07, 2022 3:15 pm

Re: Holley 600 Vacuum secondary tuning issue.

2022-02-07T14:38:35+01:00

Statistics: Posted by rgalajda — Mon Feb 07, 2022 2:38 pm

Re: Holley 600 Vacuum secondary tuning issue.

2022-02-07T06:38:23+01:00

Eric,
I disagree that the problem stems from the components, or the combination, of the engine build. None of it is overly radical & 15-17" of vacuum should produce clean plugs. While 16* of idle timing is ok, & not cause your current problem, more would be beneficial. Easiest way is to use a dist with adj vac adv, connected to manifold vacuum. See the link below for more info.

Can you stall the engine by screwing the mixture screws in? If not, then that is a problem & could be THE problem.

I never liked the Holley PV system, it is a real mickey mouse arrangement. A very soft spring balanced against the characteristics of the rubber diaphragm to set vacuum? What happens to the rubber characteristics with heat & immersion/drying out in fuel. Is a 8.5 PV still 8.5 after a few months?

So I would be looking at the PV system &/or porosity.

As far as 600 AFB v 600 Holley. Loooooong before Edel got into re-making Carter AFBs, they compared a 9625 AFB with a Holley 600 6619 carb on a 350 Chev.
The AFB made 17 hp more, 17 more ft/lbs & used less fuel doing it.....PM me if you would like a copy of the test. Also, if you think Edel was biased, a little known fact is that Edel were selling modified Holleys around that time.

MVA benefits, scroll down to post #6.
www.hotrodders.com/forum/vacuum-advance ... 47495.html

Statistics: Posted by GTO Geoff — Mon Feb 07, 2022 6:38 am

Re: Holley 600 Vacuum secondary tuning issue.

2022-02-06T23:09:17+01:00

rgalajda I hope I listed like you requested. Thanks for your time and input and its appreciated.

Statistics: Posted by eric76 — Sun Feb 06, 2022 11:09 pm

Re: Holley 600 Vacuum secondary tuning issue.

2022-02-06T23:12:11+01:00

Holley jet kit 60 through 99 on hand.
Brass allen set screws drill to size if needed. 6-32,8-32,10-32.
Air bleeds 10-32 drill to size from Quick fuel
pump cam kit and shooter size kit .020 to .040
vacuum secondary springs all colors

Statistics: Posted by eric76 — Sun Feb 06, 2022 11:06 pm

Re: Holley 600 Vacuum secondary tuning issue.

2022-02-06T22:46:35+01:00

I mean a list of jets , bleeds , restrictors, etc

Statistics: Posted by rgalajda — Sun Feb 06, 2022 10:46 pm

Re: Holley 600 Vacuum secondary tuning issue.

2022-02-06T22:29:02+01:00

rgalajda 600 Holley 1850-14.

Statistics: Posted by eric76 — Sun Feb 06, 2022 10:29 pm

Re: Holley 600 Vacuum secondary tuning issue.

2022-02-06T21:57:18+01:00

Again a simple list, no comments

Statistics: Posted by rgalajda — Sun Feb 06, 2022 9:57 pm

Re: Holley 600 Vacuum secondary tuning issue.

2022-02-06T21:27:27+01:00

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.

Statistics: Posted by eric76 — Sun Feb 06, 2022 9:27 pm

Re: Holley 600 Vacuum secondary tuning issue.

2022-02-06T20:45:55+01:00

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

Statistics: Posted by rgalajda — Sun Feb 06, 2022 8:45 pm

Re: Holley 600 Vacuum secondary tuning issue.

2022-02-06T16:32:33+01:00

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.

Statistics: Posted by eric76 — Sun Feb 06, 2022 4:32 pm