Thanks for your input wedge. I have wondered about Positive crankcase ventilation effects on tuning a carb, but no one talks about it.
I been working on the Holley today. Some think there is nothing to adjust or tune on a Holley, but they would be wrong! There are a lot of things that effect each other and you have to tailor the tuning to the car. And there are a lot of things that can be done.
So, today, after getting my vacume gauge , and adjusting idle mixture at 650 RPM. I have 12.5 to 13 inches of vacume. I put in a 6.5 power valve. I have read several adjustment procedures for setting the accelerator pump and they can be a little conflicting. I set mine so that the pump lever and the pump arm have no clearance at throttle closed position ( idle) there should be about .015 clearance at wide open throttle so that the pump diaphram will not tear or bend any pump linkage. I still need to check my float level.
I didn't get to test drive as there were storm warnings . Wifey and the dogs went to the under house storm shelter , and I was close by ! Several tornados in the area with a country home about 4 miles away got hit. We had damage from golf-ball to baseball size hail . Broke some chunks out of our new homes vinyl siding and I am afraid to go look at the roof !
BTW does anyone know how to test to see if a power valve is working ? .............................MO
On Tuesday, June 27, 2017 at 9:01:11 AM UTC-5, wedge wrote:
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.
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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