Holley racing mods
 

Hey all,

I've been battling a horrible engine stumble in turns from my Holley Carb.... I installed the center hung float bowl kit, and the stumble got a little bit better... but it's still there.... Anybody have any suggestions? One idea I had was to get an offroad vent tube.....

Dan

TTT...

Anybody?

Dan

wish i had any ideas for u... i'm gonna be running a holley with regular side mounted float bowls, course if u can't figure this out, i may not upgrade to the center float bowls, i may just put up with it till i can afford the megasquirt and holley based throttle body and injectors...

Well, I have a couple updates today...

Got to run the car a bunch at an autocross today... about 20 runs... Tried numerous things, and was able to KILL the dreaded stumble... I ended up having to run the float levels real low!!!! not running into any problems with running out of gas, but I'm doing a track day at VIR next weekend too, so I guess I'll find out the hard way...

Dan

When I was road racing my brand X I had a little trouble with my Holley. The carb was sideways mounted like an RX7, but higher and on the driver's side. :) My float level was too high and the car was flooding on a long left hand corner. If I switched off the fuel pump before the turn the car didn't stumble so I knew it was flooding. Other folks have had good luck with connecting the bowl vents with a piece of hose with a hole in the middle and also using jet extensions. One problem with V8 cars is killing the engine in the stop box as fuel suges forward in the rear float bowl causing fuel to run out the vent into the air horn and also through the main circuit into the boosters. The rear jet extensions cause the jets to loose pressure under braking mitigating that slosh induced problem. Since your carb is sideways you may need to do jet extensions on the primary and secondary sides.

Thanks for the info... Yeah, for my next mod I did order the Holley off-road vent tube... It basically is just like the hose you're talking about, but the whole thing is metal...

Dan

That isn't the J-tube is it?

50cc accelerator pump upgrade. I don't know if your holley is vacuum or mechanical secondaries, but if it is the mechanical secondaries (double pumper) and it is stumbling when you accelerate hard then you would want to upgrade the acceperator pump to the 50cc one (on the secondary if double pumper). This way when the secondaries open or you throttle it suddenly there is a larger squirt of fuel to compensate for the sudden increase in air flow. I have a vacuum seconary holley 600 and upgrading the accelerator pump made all the difference in the world! just make sure to set your floats correctly after upgrading the accelerator pump as the pump now has a higher volume squirt and takes more from the bowl. float bowls should be set so that when you remove the check screw fuel hardly spills out.

I have a 600cfm double pumper and I have the stock 30cc pump diaphrams. It works fine.

50cc pump is overkill (for a 1.3 liter). If you need a bit more volume out of the accelerator pump then changing the pump cam will do the job 99% of the time.

Jet extensions in both the primary and secondaries is a great idea (as stated earlier). Center hung float bowls are also a great choice.

-Marques