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 long 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 some 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 did have the jet extensions on the front floats, until the Holley rep advised me to use them on the rear only. He said they would uncover under acceleration. But in any case I still had the issue when the jet extensions where on the front. The jet extensions are now on the rear bowl. And I am using the Nitrophyl floats. But I am tempted to put a set of notched Nitrophyl floats with the jet extensions back on the front to see if the problem lessens,

BTW, a warning to all who use the jet extensions with the Nitrophyl floats, be sure to use the floats notched specifically for the jet extensions,

http://www.summitracing.com/parts/HLY-116-10/

otherwise, even though you will install the float bowl with the extended jets UNDER the float, the regular Nitrophyl float will eventually catch on the extended jets and cause flooding.


any ideas

thanks,

Z. Ray
'66 GT-350
original drivetrain, sheet-metal, interior, & paint

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