dies on heavy braking
#1
dies on heavy braking
First of all, hello to all of you on the other side of the fence. I have a healthy respect for all the accomplishments of the bow tie world. And I'd be the first to admit my side would be nothing without a strong adversary to compete against.
Now that the love fest is over, here's my situation, I'm using a Holley 650 dp on a Hi-Po 289 GT-350 with a Paxton. With or without the Paxton the engine dies on heavy braking. Setting the float level lower or higher on either bowl has no effect on my problem. I've ruled out any ignition related cause. I have a wideband a/f gauge installed and can see the mixture get richer & richer as I'm braking 'till it hits 10:1 & the engine starts to die. With the Paxton disconnected I can attach hose extensions to the vent tubes, and am reasonably certain no fuel is coming up the hoses. However, I can see that the tops of the secondary butterflies have gas on them. Where could this be coming from? I didn't hit the gas hard enough for the secondaries to be moving, so I'm thinking it could not be coming from the secondary accelerator pump shooters.
any ideas ???
thanks,
Z. Ray
Now that the love fest is over, here's my situation, I'm using a Holley 650 dp on a Hi-Po 289 GT-350 with a Paxton. With or without the Paxton the engine dies on heavy braking. Setting the float level lower or higher on either bowl has no effect on my problem. I've ruled out any ignition related cause. I have a wideband a/f gauge installed and can see the mixture get richer & richer as I'm braking 'till it hits 10:1 & the engine starts to die. With the Paxton disconnected I can attach hose extensions to the vent tubes, and am reasonably certain no fuel is coming up the hoses. However, I can see that the tops of the secondary butterflies have gas on them. Where could this be coming from? I didn't hit the gas hard enough for the secondaries to be moving, so I'm thinking it could not be coming from the secondary accelerator pump shooters.
any ideas ???
thanks,
Z. Ray
Last edited by zray; 08-23-2009 at 11:06 AM.
#2
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Re: dies on heavy braking
I've got the same problem... I thought about putting jet extensions in the primary fuel bowl but i read that can cause you to go lean with normal driving. I had figured the fuel was sloshing in the bowls... but I'm not sure. I figure it's either sloshing fuel, the shock to manifold vacuum, or maybe my idle screws still arent set quite right. Adjusting the floats doesn't do anything. I've also got a 650 DP but from some research on the internet I've seen people switch from carbs that hd a problem with that TO Holley DP's and the problem went away. So it's gotta be a tune issue somewhere... or at least, it's not a 650 DP problem.
Last edited by InfernalVortex; 08-23-2009 at 09:52 PM.
#3
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Car: 91 Firebird, 06 Dodge Ram 1500 SLT
Engine: 3.1L, 4.7L
Transmission: 700r4, 45RFE
Axle/Gears: 3.23 open, 3.55?
Re: dies on heavy braking
Im not a carb person but it sounds like a vacuum problem to me. I could be wrong tho. Just trying to help.
#5
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Car: 82 Berlinetta/57 Bel Air
Engine: LS1/LQ4
Transmission: 4L60E/4L80E
Axle/Gears: 12B-3.73/9"-3.89
It's coming from the secondaries. If you concentrated your attention on the primaries, it's time to refocus on the secondaries.
#6
Re: dies on heavy braking
#7
Re: dies on heavy braking
yes the bowls are center hung
carb is new, like this one. http://www.summitracing.com/parts/HLY-0-4777C/
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#8
Re: dies on heavy braking
To the best of my knowledge, the only place it could be coming from with the way you describe it is from the bowl vent.
30 years ago I saw a plastic deal for a Holley bowl vent that looked like a kids whistle. It went in the slot on the metering block and extended towards the float. It was made for this exact situation, but I haven't seen it since then.
30 years ago I saw a plastic deal for a Holley bowl vent that looked like a kids whistle. It went in the slot on the metering block and extended towards the float. It was made for this exact situation, but I haven't seen it since then.
#9
Re: dies on heavy braking***UPDATE***
To the best of my knowledge, the only place it could be coming from with the way you describe it is from the bowl vent.
30 years ago I saw a plastic deal for a Holley bowl vent that looked like a kids whistle. It went in the slot on the metering block and extended towards the float. It was made for this exact situation, but I haven't seen it since then.
30 years ago I saw a plastic deal for a Holley bowl vent that looked like a kids whistle. It went in the slot on the metering block and extended towards the float. It was made for this exact situation, but I haven't seen it since then.
I just have determined the problem lies in the accelerator pumps circuit. I had them adjusted per Holley's instructions, with a little pre-load, so the action is immediate. The problem was, when the brakes are on hard, the throttle linkage is tweaked enough to give a squirt of gas into the closed carb venturies. I tightened up on the acc. pump screw slightly, which gives a little clearance before the acc. pump is activated. This one about drove me off the deep end.
thanks for all the help,
Z. Ray
#11
Re: dies on heavy braking***UPDATE***
A guy over on the Cobra forum had the tip. I think most of the Cobras use a solid accelerator linkage vs. the more modern cable set-up.:
http://www.clubcobra.com/forums/index.php
Z. Ray
#12
Re: dies on heavy braking***UPDATE***
Are you running poly motor mounts, or rubber? Also, interesting that you say the whistles are a stock item. They aren't listed as a service part on Holley's web site.
Last edited by w5ga; 08-25-2009 at 10:20 AM.
#13
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Re: dies on heavy braking***UPDATE***
you may have a throttle cable arrangement, but I've got the old fashion solid rod type linkage. The brackets aren't moving, but the engine mounts, linkage rods & bell-crank appears to have a little movement from the braking forces. And I had the acc. pump cam preloaded enough so it was squirting without much force needed,
A guy over on the Cobra forum had the tip. I think most of the Cobras use a solid accelerator linkage vs. the more modern cable set-up.:
http://www.clubcobra.com/forums/index.php
Z. Ray
A guy over on the Cobra forum had the tip. I think most of the Cobras use a solid accelerator linkage vs. the more modern cable set-up.:
http://www.clubcobra.com/forums/index.php
Z. Ray
Wont apply to me then.
Oh well I doubt i'll ever figure it out to be honest.
#14
Re: dies on heavy braking***UPDATE***
http://www.summitracing.com/parts/HLY-0-4777C/
here is the Holley part number for the whistles
http://www.holley.com/26-89.asp
http://www.summitracing.com/search/?...%2026-89&dds=1
the motor mounts are Ron Morris poly mounts, I guess the linkage was supplying most of the movement.
http://www.ronmorrisperformance.com/...Code=Eng_Parts
thanks again for all the replies & help
Z.
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