Carb guru Help needed

[swifter]

Engine small block chrysler,850 carb with the following:
prim jet:74
sec jet:82
prim pwr vlv:4.5
idle feeds: .032
sec pwr vlv: blocked off
prim & sec shooter .035
main air bleeds: .036
idle air bleed:.075
the low down--I have a/f meter at idle-12 afr normal drive thru gears never goes above 13 afr--problem-when I stick the throttle(pedal to floor) the afr hits 20 (very lean)sputters the recovers and pulls like a raped ape-This is ONLY happening under full hard accelerating like a run down the track help me out please!!!!!!!!!! DO i need to reduce main air bleeds to richen up mixture under hard accelerating???????? Thanks Steve

 

[Oklacarcollecto]

You might want to also post this on FBBO since Rob (StrokerScamp) is now over there. There are other members here that will help too.

 

[70aarcuda]

first check to make sure your acelerator pumps are working correctly...that as soon as you move the throttle blade it shoots gas..also make sure the secondary pump is adjusted correctly..as the secondaries begin open once the primarys hit 40 degrees....


also...what kind of vacuum are you pulling...as the power valve might be too low

 

[oldkimmer]

.............with a 750 u might be good.............with a 850 u need to jet up 4-6 sizes on the front.......kim...........

 

[swifter]

THanks Guy's keep it coming--Steve

 

[70aarcuda]

most 850 holleys are jets 80s square..with power valves in front and rear....so if you blocked off the rear power valve and did not jet up...it is lean..

 

[OldmanRick]

With the secondary PV blocked i suspect you are still a little lean on that side, even with 82s. If you have larger jet readily available i would try them, jmo. Squirter size should be plenty unless you've got a big open plenum and a tall spacer, do check adjustment and operation as stated above though.

 

[crackedback]

I don't know what you have for a cam, but, what kind of initial timing are you running? The idle could be cleaner than in the 12's. What's the A/F profile from 4000-shift points?

Is this a proform main body?

Bigger bleeds generally means leaner, it's the opposite of main jetting. If that came with .073/.033 and you have .075/.036 in it now, you've leaned both circuits out.

Check what AAR mentioned, the squirters and pump arm would be first place to check.

 

[swifter]

Holley hp main body--4000 shift points?????? it is a 4 speed i'm shifting at 5500 to 6500 and yest open plenum single plane manifold--Thanks Steve

 

[OldmanRick]

Steve, what "crackedback" was asking is what do the A/F ratios do between 4000 and your shift points, like if you charted it on a graph.

 

[swifter]

ok thanks--Steve

 

[swifter]

it runs anywhere from 10 to 12 till you punch the throttle then spikes to 20 (lean) then it spits and sputters till it recovers after it recovers(1 to 6 seconds) it pulls like a mule and a/f goes to 11 --hope this helps Steve

 

[swifter]

so whatever is happening is the transition from part throttle to w.o.t--Steve

 

[OldmanRick]

Unless the sec'd pump is completely malfunctioning, there may be some work to do on the bleeds? Although i still think you can jet up a little.
I'll let "cracked" address the air bleeds since i don't have a lot of current working knowledge there. Back in my day we filled'um with lead shot and drilled'um with a pin vise...lol.

 

[swifter]

The guy who built the carb told me to change the main bleeds from .36 to .30's and test again any response????????? He told me that will richen up the transition from the primary to secondary wot pull--Steve???????????

 

[OldmanRick]

The guy who built the carb told me to change the main bleeds from .36 to .30's and test again any response????????? He told me that will richen up the transition from the primary to secondary wot pull--Steve???????????

That's the right direction. As for a specific number to try, to me, that's as good as any. Was hoping for some other responses. I was gonna suggest getting a assortment to try and dial it in, but i looked them up and those babies ain't cheap

 

[crackedback]

bleeds are for making MINOR adjustments to the fuel curve. Not what you have going on IMO.

Still waiting for some answers. Tons of carb issues aren't rooted in the fuel system.

How about some info on the engine. Asking this type of question is one where shooting blind doesn't get good answers.

 

[swifter]

engine: 11-1 comp. 3.92 bore 4.050 stroke cam- 106 center line,616 lift intake,622 lift exhaust,.050 duration 243 intake, .050 duration 251 exhaust,1 3/4 od prim headers, 3in exhaust, 4 speed car,3.91 rear gears, 28x10 rear tires-----Steve

 

[crackedback]

What is the timing? Initial and total?

 

[swifter]

10 initial ---from 10 to 28 from 2000-3000 and 28 from 3000 to a rev limit of 6800

 

[crackedback]

Not enough initial. I don't even run stock 318's at 10*, they all have in the 12-14 range. You have tons more cam than a stock 318, needs more initial. There's most likely your rich idle issue. If you reach in a twist the distributor CCW and it picks up RPM, you have your answer.

I'd turn it to 20-24 and don't drive it! See if it starts when warm, it should. If it doesn't and drags really hard or kicks back, take a couple degrees out until it starts. Reset the carb for idle speed and idle mixture. It should clean up a bunch.

Once you get the idle part of the equation sorted out you'll have to limit mechanical in the distributor to hit you total number. 28 is pretty light on total unless it's got a really efficient cylinder head.

It will run like a different car at idle and shouldn't gas out the entire neighborhood. It will be a bunch snappier.

I'd restart tuning at the baseline settings, .075/.036 bleeds. The idle air bleeds may want .072, BUT, do that after you get the timing and adjustment done. Primarily if the cruise is a little lean, step down the idle bleef and readjust the idle mix screws (it will change). Shoot for leanest best idle using a vacuum gauge and see where the a/f falls. Should idle pretty easily around a 1000 or so RPM.

No amount of dickering with the bleeds would help what you got going on.

Here's where I'd shoot to start as far as a/f's
Idle 13.5-14.5
Cruise 14.0
WOT 12.5-12.8

Good luck with it.

 

[swifter]

THanks!!!!!!!!!!! Will get to it and report back!!!!!!!!!! Steve