I've had this problem forever and can't get rid of it. There is a dead spot in the transition around 2400 rpm. I have the lsab blocked and have tried every combination of pump cams and squirters avaliable. I can watch it when I rev it up in park, the pump shot goes and the motor goes lean then the booster comes on and it revs clean after that. The only thing that has worked to get rid of it was to go up 3 jets in the front which made it low 11 afr while cruising. Would annular boosters help with this?
What else can I do to fix this?

 

Ok, I realize I didn't really give any info in my first post so here goes. 355 sbc with 8.7:1, solid roller,s475 1.32ar, timing locked at 38* pulling 15* on 12-13psi. trans is a th400 with a custom converter and 3.42 rear with 275/60's. the carb started as a 750 hp, I added brent davis metering blocks and I recently added a pro form main body with annular boosters that didn't change anything.
ifr-.035
front and rear lsab-blocked
hsab-73
pri-72
sec-72
pvcr-.065 front and rear
front acc pump-green cam 35 squirter
rear acc pump-pink cam 31 squirter
Idle 13.7-14.5
cruise 12.5-13.5
wot 11.4-11.5
When I wrote the first post I was at 70pri-71sec with .077pvcr the only difference was the cruise was mid 14's, going up in jets didn't really change much like I thought it would.When I foot brake it, it goes dead lean at 2000rpm and if I back off the throttle it'll push through it, if I don't it basically shuts off. When i'm cruising and I try to mash it, it jumps,then dies(shuts off) then pushes through it and goes into boost at about 4500 and runs awesome after that. When it dies it always reads lean. ANY help is appreciated!

 

Seems like the real smart guys have been quiet for awhile.

Just to try and understand a little better, in the first post you talked about free reving then second post you talk about foot braking it. Is it doing it during both situations?

 

why are the idle air bleeds blocked?

Are the boosters flowing at 2000rpm on the foot brake?

 

I'm not real sure if the boosters are flowing on the foot brake, I was thinking blocking the lsab would help bring in the boosters faster. Yes it does this in both free revving and foot braking.

 

I think you got your terms backward or posted the information incorrectly. On post #2 you have .073 Hsab and the LsAB blocked. On you last post you mention blocking the Lsab to bring the booster in faster. OK. So lets back up a bit. Lsab (aka: iab or idle air bleed) effects your idle and the transition which is your low rpm driveability and response. HSAB is only effects the main circuit which feeds the boosters.

LSAB's are the outer restrictors
HSAB's the inner retstrictors.

If you truly have it setup as in post #2 then I can see you might have an issue. .073 HSAB would make the main circuit come in very very lazy. And having the LSAB block would make it start hard and peeder out about the time the main circuit should be taking over.

Put the .073 restrictors in the LSAB location (outers) and block the HSABs and report back.

 

Ok, you are right. I had the terms messed up. The 73 is the lsab and the hsab is blocked.

 

DAng! Well, that blows away what I thought was going on.

 

Is there by chance a restrictor in the main body in the port that feeds the transition slot?

 

I'm not sure what to look for. I have an aluminum annular pro form main body. I'll have to take a look

 

They dont put them in so I doubt it has a restrictor in it.

What fuel?

 

Pump 93

 

supercharger or turbo?
Vent tube exteensions?

 

If the lsab is 73, could you drop it down to say a 60 to try that? I would think that would fatten up the transition a little.

 

It might be worth a try. On gas its gonna make it supper rich just off idle and will lean as more of the transition gets uncovered. Well, thats been my experience.
73 usually works well on gas.

So the only thing original is the base plate correct?

 

I'm running a turbo, s475. No vent tube extensions. Yeah, I guess the base plate is the only original part left on it. I will try making the lsab smaller and see how that works. It'll probably take me a few days before I can test it again, I will report back. Thanks for the help.

 

I guess you wouldnt need to jump as big as I suggested. I like to make a fairly big move (when adding fuel) when making changes to hopefully see/feel solid results. Maybe it is too big of a jump for lsab's though as it is a delicate circuit anyhow.

 

what kinda of hat?

 

Extreme velocity hat.

 

divider in the hat?