Re: Power valve.

You will need to fine tune it between a 4.5 -6.0 they come in .5 increments. 12.5 divide by2 so try a 6.0. I went through same thing, slight hesitation. Also this worked for me. I read the throttle blades should be open .020 (use a piece of wire) . Never heard of that so I tried it and it worked for me. No more stumble etc when driving off. This may all be bs but it worked for me and and took some time but turned out great. Every engine, every carb is different, you have to find what each one likes. Timing curve and even pcv valve has an effect. Pcv valves ad air in different stages , rates ,etc. Something no one ever thinks of is that and how they work or effect tuning. Not all created equal. Also the (main jet) is only a cruise jet. The real main jet is the power valve channel restriction behind the power valve. Remember the old power valves had holes and the window style PV was the step up. I used a two stage PV on a 600 that was jetted down from 66 to 60 looking for mileage. When i installed the two stage PV truck wouldnt run...no fuel. That PV wasnt passing enough fuel. Reinstalled bigger jets, it ran. Called Holley told them whats up with PV and its effect , no one had an answer or would give me an answer to what was obviously going on. Ended up with a 30 dollar PV in my tool box and reinstalled regular PV and smaller jets. Cost me a bit but I learned you need a metering plate that you can make your own changes to. Kinda like when working on an Eddy carb and Eddy telling me when you figure it out call us and let us know....What worked in that case after two months of fiddling...threw it in the trash and put on a Holley. Holleys can work as good as FI they just need tuning and all other systems need to be right PCV valve included. It is a fine symphony. If you look at a Holley it has 10 holes that always leak fuel constantly. Boosters, idle slots are in all four bores , transfer slots and the squirter , as air moves by it it is pulling fuel from there also. We won't get into who owns Holley and its cohorts who are screwing us all. Just my thoughts maybe it will help or at least give you something to think about.

On Tuesday, June 27, 2017 4:11 AM, MO <micher@xxxxxxxxxxxxxxx> wrote:

I am trying to figger out a stumble in my Holley 4250 with mechanical secondaries--750 CFM. Low gear, rolling at idle, punch the throttle and get a substantial hesitation--not really a bog. about 1500 RPM at full throttle it takes off like a striped a**ed ape!. I think I have plenty of accelerator pump now. I put a 2.5 power valve in because I thought I had low vacume ..my bad. I put the vac gauge on and actually have 12.5 inches at idle. Do I just put a 6.5 power valve in, or is there a better way to know which PV I should use? BTW the engine idles fine, but I have not fine tuned the idle mixture yet. .............................MO

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