spark plug help?

Question

I would try and lean it out just a touch at idle and up the jets by 2 points to fatten up the WOT circuit ( how can i lean this carb out at idle... its a holley 750 cfm........i know how to up the jets ,but not how to lean it out at idle) thanks

Answer 1

make sure the choke is fully open when the engine is warm...

you will also find the idle mixture screws on each side of the primary float bowl. screw both of them in untiil they seat then back them out 1.5 turns...then adjust each side seperately until you have the highest RPM at idle...

Answer 2

Please do a vacuum test on uour motor at idle. Jot it down. Pull off both float bowls and one at a time inspect the power valves on the side facing the carb. body. If you detect any gasoline inside the main carb where the end of the power valve faces the carb body the power valve diaphragm may have ruptured. Look clocely at the hex on the powervalve. There will be a number stamped on the hex. It may say 5 - 5.5 -6 -6.5 -7 -7.6 -8 -8.5 ---all the way up to 14. The deal here is to replact the power valves with a number lower than yor idle vacuum that you have written down by at least 2 complete numbers. When you re- assemble your carbuerator use genuine Holley gaskets on the float bowls and the back side of both metering bodies.
When you start it up check the site plugs so that fuel just touches the lower thread openings on the primary and secondary ends. Jet changes do not chance the idle mixture. The idel mixture screws in the side of the metering block irons out that mixture. Use a good vacuum gusge for this.If your plugs appear brown or grew after a WOT run cut the ignition and inspect the plugs again. Excess ideling distroys clean plug reading. Inspect the very base of the porcelian around the center electrode for color. A plug flashlite works best for this. If you need to lean the carb do it one jet size at a time. Strive for a clean light tan or very light grey color. No shades brown or green.

I hope you don't have a double pumper. In our experiance they make less driveability and are a total waste behind an automatic transmission. They are only marginally better with a stick and very low rear end gears.

I had a blue printed 425 hp. 427 inch Chevelle which had the factory 750 vacuum secondary Holley which ran like "gad zooks." I sold the car and the guy spent a mint on an 850 double pumper and the car went slower in the quarter mile by 3 /10. It had a slippery converter and 3.73 gears but it just would run as well as the vacuum secondary (softer diaphram spring) carb.