650 brawler double pumper

[77k5]

Hello, I am new to fine tuning holley carbs, I have purchased four holley style carbs, (all new), 1850 street warrior, quick fuel off road 600 vacuum secondary, fst 650 vacuum secondary, and the latest, brawler 650 double pumper, side hung floats and single feed, (for off road). I have gotten them all to run pretty well but not perfect except for the fst, (would not even run at all out of the box) so I took it back to summit for a refund.

So I will just go with the brawler for now.

First up I added a 1 inch open spacer to a gm dual plane intake and it helped with all the carbs, better idle and seem to make my engine pull harder everywhere. Then I put on the brawler and it was not perfect, (rich everywhere), but it pulled harder than all the other carbs. I have since dropped the ifr's from 31 to 28, ( four corner idle), seem not to do much, (70/70 iab's). T-slots are about .025 to .030. Dropped the primary jets from 70 to 66, (mab's 28/28). Three hole emulsion blocks front and rear, (checked all holes .028). Primary pump nozzle .021 with a blue pump cam, (was .031 orange cam). Secondary 74 jets with a .028 pump nozzle and a orange cam, (front and rear cams on # 1 hole). Cleared up a lean spot with a 7.5 power valve, then a bit rich so I dropped the pcvr's from .043 to .040, seemed to lean it back down a bit. Still not perfect but getting better.

Anyway, can you guy's tell me the best way to set the idle on a four corner carb, (still rich) and I still have a bog when getting into the secondary,s, Ordered another blue pump cam for the rear.

Engine, gm sp350/357 crate engine
9to1 compression
Vortec heads
G.M.dual plane intake, 1 inch open spacer
hyd. roller cam
215 @ .050 int. 223@ .050 exh.
.473/.473 lift
108 lsa
hedman header's , dual exhaust , borla pro xs muffler's and h-pipe

Timing , checked tdc.
22 degree's initial with 6 degree's added with vacuum can , (full vacuum)
34 degree's total, (limited the h.e.i.)
All in by 2,800 rpm
And I live at 5,500 feet elevation.

Thanks.

[Right hand drive]

The first bit of advice most guys here would give is to lower the idle feed restrictions in the metering block. this gives a more stable, consistent metering of idle fuel. Someone will have a link to how this is done but its just a matter of tapping x4 ifr holes at the bottom of the idle channel in an existing hole adjacent to main well idle fuel exit.

The way I set the curb idle screws is with a vacuum gauge and with your small cam will be sufficient. Plug it into constant idle vacuum source. bottom all 4 idle screws and turn out x3 half turns (I find it easier to work in half turns). Start the engine. It should start but will run rough. Turn all 4 in 1/4 turn. If it idles better and vac is up turning in (leaner) is the right way to go. Go another 1/4 turn each screw, let it settle and if idles better with increased vac go again. You will reach a point where the next 1/4 turn will have a negative affect. This is where you then back out 1/8th turn until you find the sweet spot for highest stable vacuum. I find a lot end up finalized at 5/8ths to 1-1/8th turn from seated.

There will be other methods but that's what works for me.

[77k5]

Thanks right hand, I am on it and I may go for the lower ifr's if I cant get the idle I want. With the front t-slots set at .025 do I need to do the same with the rear? Right now I have not done anything to the rear stop screw so there is no t-slot visible in the rear, only the front.

[Right hand drive]

Use the secondary adjustment to prevent excessive primary t-slot exposure.

When the Brawler is off next take note, or better a few phone photos of where the idle speed screw head slot orientation (north/south? East/west? In between etc) is for the squared t-slot. Then adjust for slot double length than its width. Record screw head slot orientation for that setting. Do the same with secondary but only find where barely cracked open and square t-slot is. If those Brawlers have the little grub screw underneath in the baseplate it is easier if you flip the screw to get access from the top. Return to square setting pri and just cracked open sec and bolt on engine. You will now have reference of when the throttle blades are at your starting square point and a point of where t-slot exposure is beginning to get excessive on the engine. If you need to go past the t-slot double width length pri setting for idle speed then stop there and start using secondary screw. It shouldn’t take too much. Test drive.

Another way and one to use if your engine can’t handle too much pri t-slot exposure is that if all t-slots are the same length and depth on the baseplate is set both primary and secondary slots with the same square t-slot. Using the above method of recording screw head orientation adjust pri/sec the same each, ie instead of half turn on pri only then a qtr turn each.

First method would prevent unnecessary fuel coming through secondary t-slots at low speed, second is to improve any transition problems that remain with first method.

If you have an auto do preliminary idle mix and speed adjustments in neutral and then, with an assistant in gear.

[jmarkaudio]

Idle feed location
https://www.tapatalk.com/groups/racingf ... t-t18.html

T-slot jet location. Start at .082, I use 8-32 x 1/8 brass set srews and 4 turns on a bottoming tap to keep it from going in too far.
https://www.tapatalk.com/groups/racingf ... t1392.html

[77k5]

The idle is pretty good with the .025 t-slot primary and none showing on the secondary side, I was just wondering if that was correct. With the .028 ifr's the mixture screws are all 3/4 of a turn out and the afr gauge is 12.5 to 12.9 and if I lean it up to say 13.5 the engine does not like it and the vacuum drops. I just thought maybe messing with the secondary t-slots might help out a bit. I just got my blue pump cam for the secondary's so when it warms up I will put that cam in and see if it cure's my bog when they open.

Thanks again, great reading on here

(jmarkaudio),I may tackle the t-slot jet and the ifr lowering as well, I am just a little spooked about doing that on my new carb. Although I do have a carb shop near me so I could have that done there. I talked to him a while back and he is a fan of the upper location for the ifr's but he will do whatever you want.

[Right hand drive]

If idle is good with correct pri t-slot exposure and you don’t need to expose secondary t-slot then all is good.

Idle AFR is ok at what you have, stick with highest vac. My apologies, I interpreted your first question of the best way to set the idle on a four corner carb as looking for a stable, consistent idle, not leaner idle. You will likely find that if you change up iab’s and ifr’s to lean transition fuel your engine will still want the 12.5 - 12.9 idle fuel for best vacuum. You may be getting good combustion at idle whereas guys with bigger cams idling in the 14s would likely be being told lies by their gauge and in reality idling richer than indicated. Any little misfire from incomplete combustion at idle will be sensed as lean as the unburned oxygen goes into the exhaust. My 383 likes to idle with the gauge reading 13.2-13.4 but with a cam of 245@ .050” and 28* overlap it would be truly richer than that.

Getting into the secondaries bog, is that flooring it from cruising on the primaries or progressively using part of the secondaries?

If going from closed secondaries to wide open in one hit you are using all of the pump cam. The pink cam gives a bit more total volume. The 31 squirters and pink may work for that situation. Bigger squirter you get all that volume sooner. If your already a little into the secondaries then give it a bit more and it bogs the 28’s and blue cam might do the job. Just remember with a blue in the primaries you have likely spent it before or barely into the secondaries so no help from the primary squirter.

[77k5]

Thanks again right hand drive, Just got snow last night so it may be a day or two before I get after it again

When the engine is warmed up and at idle and in neutral you can snap the carb. just using the primary's and its all good. If you snap it hard getting into the secondary's there is just a slight hiccup and then it rev's up.

Driving, if you mash it from a stand still it falls on it face and then takes off, if you take off fairly hard but not floored its all good. On the highway, if you mash it at highway speed, (2,900 rpm) it hesitates slightly and then take's off.

When it warms up I will get after pump cams and nozzle's, thanks again

[gntkllr]

In Holley's own picture on the website of the pretty purple base plate underside, I can see what certainly look like secondary constant idle feed holes below the secondary throttle plates in the extra large picture, and in reflection on the throttle blades in the smaller image below... which a 4-corner idle carburetor does not need. Those, if present on yours and drilled through to the transfer slot vertical passage, should be blocked. Idle air:fuel should come from the mixture screws, front and rear. This (secondary constant idle feed holes are usually also much bigger (large idle air:fuel contribution - probable minimal mixture screws' turns out reason) than what's needed where/when they are needed (2-corner idle)) is another of their "new and improved" aspects to what amounts to jacked-up calibration right out of the box.



In order to smarten these up, like Mark mentioned above... factory up-high idle feeds should be removed, ideally-sized (0.031" should suffice with your camshaft) idle feed restrictions should be installed down-low, and 0.082" transfer slot restrictions installed in the main body due to the effects of their usual transfer slots being too wide/long... starting with 0.070" IAB's is good...

Additionally, for smartening up of the main circuits, to make it work even better with the above improvements, with 0.028" PMAB's and 0.025" SMAB's... the middle (of the three 0.028"?) booster correction ("emulsion") bleeds should be blocked or have blanks installed... your 7.5"Hg power valve makes oodles more sense than the silly factory 4.5... then, with 0.063" primary-only PVCR's, something like #72 PMJ's and #82 SMJ's could go in...

Less having to fiddle with factory cams/shooters should be the result too...

[Right hand drive]