CarburetorsCarb discussion and questions. Upgrading your Third Gen's carburetor, swapping TBI to carburetor, or TPI to carburetor? Need LG4 or H.O. info? Post it here.
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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.
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.
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Last edited by InfernalVortex; 08-23-2009 at 10:52 PM.
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.
You say under heavy braking. Are you autocrossing? If so, are you using center hung float bowls? If not, you should be.
Quote:
Originally Posted by fleetmgr
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.
those "whistles" now come as std. equipment on the dp Holleys. So I already have that.
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
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'66 GT-350
Original Drivetrain, Sheet-Metal, Interior, & Paint
Explain hwo the throttle linkage gets tweaked under braking? Are you saying the g-forces are moving the brackets just enough to trigger the squirters?
I may try this then...
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.:
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.
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.:
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.
The whistles came installed already when I bought the carb new a few months ago from summit. This one:
