dies when braking hard

zray · August 23, 2009 at 11:07 AM

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

cobraboy · August 23, 2009 at 11:46 AM

Ray

Do you have a split powervalve ?

zray · August 23, 2009 at 12:23 PM

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>

Ray

Do you have a split powervalve ?

no, it's a single stage & I've gone all over pv range trying different ones, but this issue seems unrelated to power valve.

Z. Ray

cobraboy · August 23, 2009 at 12:31 PM

I have a vac secondary Holley so do not know much about double pumpers, but assuming the secondary system on yours is the same as the primary I wonder if the check ball and weight under the secondary shooter are free and are seating ok if not perhaps some fuel is being pulled up thru the secondary shooter as when you brake there will be a lot more vacuum pulling at that carb with all of the butterflies closed.

zray · August 23, 2009 at 12:47 PM

I will check them ,

thanks,

Z.

zray · August 24, 2009 at 8:25 PM

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

BoS_old · August 24, 2009 at 9:57 PM

The play between the acc. arm and the bottom of the

adjustment screw should be 0.15" for a Holley 3259 and most

others as well.

/Bo

zray · August 25, 2009 at 7:56 AM

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>

The play between the acc. arm and the bottom of the

adjustment screw should be 0.15" for a Holley 3259 and most

others as well.

/Bo

Perhaps you meant 0.015, which is the minimum clearance, maximum is 0.062. These measurements are taken when the throttle shaft is moved to the wide open position & the pump lever is manually pushed open as far as it will go.

There should be no clearance between the operating screw & the pump lever at the idle position on all the modern 4150/4160 series of Holley carbs.

Z. Ray

BoS_old · August 25, 2009 at 8:40 AM

Yes, You are correct. missed a 0, sorry.

What I do is as you said open the throttles and

pull the lever down and put the feeler gauge

in between the two. Has always worked fine on my

3259's

Glad you fixed your problem.

/Bo

zray · August 25, 2009 at 12:59 PM

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>

Yes, You are correct. missed a 0, sorry.

What I do is as you said open the throttles and

pull the lever down and put the feeler gauge

in between the two. Has always worked fine on my

3259's

Glad you fixed your problem.

/Bo

on to the next windmill.

Z.

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