Power valve problems.? or

Power valve problems.? or - 07/02/09 12:06 AM

We have a 440 with lots of tweeks done to it (aprox 425 HP). Have a 750HolleyDP on it. we moved from an elevation of 4000 feet to 300 foot. I've had problems ever since. Changed the front jets to bigger, and got rid of most of the hesitation in the launch, but now have a bad Bad miss fire (maybe backfire) after I hammer it in 1st gear (well in all gears (auto trans). Do you think the power valve might be bad?

Posted By: RapidRobert

Re: Power valve problems.? or - 07/02/09 12:25 AM

Quote:

Do you think the power valve might be bad?

I would check your plugs/wires

Posted By: mark7171

Re: Power valve problems.? or - 07/02/09 01:14 AM

If nothings leaking in the carb , backfires are usually timming.

are you driving a race car with no vacuum advance ?

Posted By: 70AARcuda

Re: Power valve problems.? or - 07/02/09 04:50 AM

try a larger squirter...

Posted By: scotts66charger

Re: Power valve problems.? or - 07/03/09 04:18 PM

The carb is not leaking. The engine runs very well when Im just cruzing around, so I dont know about the plug wires. If it runs good, (and if the plug wires were bad, wouldnt it run bad all the time?). This sounds dumb, what whats a squirter?

Posted By: stumpy

Re: Power valve problems.? or - 07/03/09 04:46 PM

Sqirter=Acclerator pump.

Posted By: RapidRobert

Re: Power valve problems.? or - 07/03/09 07:33 PM

Quote:

If it runs good, (and if the plug wires were bad, wouldnt it run bad all the time?). This sounds dumb, what whats a squirter?

There are no dumb questions only unasked ones. You didn't change anything after the move ex the jets? I think a plug/wire(s)were marginal & happened to cross the line just coincidentally after you moved unless you inadvertently jostled something during the jet change & yes a plug/wire(s) can seem OK but cannot handle the increased required voltage of full throttle. And you didn't change the timing at all?

Posted By: JimG

Re: Power valve problems.? or - 07/03/09 07:45 PM

Quote:

This sounds dumb, what whats a squirter?

To elaborate on Stumpy's reply: the accelerator pump circuit has two easily-changeable items available as a tuning aid - the pump cam and the "squirter", or the accelerator pump discharge nozzle.

Various cams are available with different profiles that allow you to tailor the pump shot to throttle position. Bog when you nail it? You need a cam that will give the most volume of gasoline. Stumble when you slightly depress the throttle? You might need a cam that gives most of it's shot in the beginning of throttle movement, like a blue #427 cam. Change to a cam with more volume but don't change the nozzle and fuel will squirt at the same flow rate, but for a longer duration.

Discharge nozzles come in various orfice diameters. You'll find that they're numbered. A #35 nozzle has an orfice diameter of .035". Increase the size of the discharge nozzle but don't change the cam, and fuel will squirt at an increased flow rate, but for a shorter duration (because the additional flow exhausts the pump sooner).

Cams change the duration and profile of accelerator pump discharge. Discharge nozzles change the flow rate.

There are also larger accelerator pumps available.

Jim

Posted By: scotts66charger

Re: Power valve problems.? or - 07/06/09 05:12 AM

Wow,lots of info. I will read through them all again, and try what you have posted. Thanxs again to you ALL for the help !! Rev. scott.