Holly carbs
Can someone one give me a link or helpful hints on adjusting a 4 barrel Holly vacuim secondary carb. I know if it's on a high performance marine you go all the way in and back out 4.5 turns. I was told that this would be too much for a street app. How do you guys go about adjusting the rest of it not just the mixture.
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What do you want to adjust?
Power Valves just screw in and out. Jets just screw in and out. Float level just adjust up or down using the sight plug and adjustment locknut and screw on top.0 -
CGR,CALL 1-270-781-9741 holley tech line make sure you know which carb you have ie 650cfm,750 dbl pumper they can help ya[:D] 0 -
quote:Originally posted by Warpig883
What do you want to adjust?
Power Valves just screw in and out. Jets just screw in and out. Float level just adjust up or down using the sight plug and adjustment locknut and screw on top.
I have everything good, but I'm trying to get the mixture right. It's not bad, but I just think it could be better.0 -
Are you referring to idle speed adjustment??
What carb is it??
Doug0 -
It sounds like the mixture screws. I found that 1.5 to 2 turns out works most of the time. If you want to do it right, set your idle speed and turn in on screw until idle increases. Turn the idle back down, and adjust the next mixture screw the same way. Continue this until you run out of mixture screws to adjust. 0 -
You can use a vaccuum guage to set the mixture, or just tune by ear. Set it to get the highest vaccuum or smoothest idle. You can buy different power valves and main jets to get proper under load fuel mixture, course if you work on race engines you already know that. On the vac. secondary carbs., you can get different springs that will retard or advance the opening of the secondary throttle valves. 0 -
What catpealer said has always worked for me.
Doug0 -
Why would you want vacuum secondaries? 0 -
Vacuum secondaries are much better on a vehicle with tall gears and an automatic, because the rate at which the secondaries tip in is controlled by the demand of the engine for air - little to no bog.
Mechanical secondaries are more appropriate for a pure race vehicle with a stick shift because one brings the engine to a steady, high, RPM to launch, and because of the already high engine speed, it is not likely to bog.
Older road race cars almost all used vacuum secondaries because throttle response was more crisp and more easily modulated coming off the corners. Examples are the early Cobras(and some Mustangs) and Corvettes, as well as MOPARS with the ThermoQuad or AVS (Air Valve Secondaries) carbs.
Unless the car is a pure race car, with short gears, it is not advisable to use mechanical secondaries. Vacuum secondaries will often improve the performance on a pure race car, when replacing a carb with mechanical secondaries.
You have greater latitude when tuning a vehicle with vacuum secondaries than with mechanicals. Also, the vacuum carb will provide significantly improved fuel milage, and (generally) more low end.
Flame away.
Doug
* edited to correct spelling0 -
By the way, "Holly" is spelled "Holley", when one is referring to the carb company.
D.0 -
quote:Originally posted by catpealer111
It sounds like the mixture screws. I found that 1.5 to 2 turns out works most of the time. If you want to do it right, set your idle speed and turn in on screw until idle increases. Turn the idle back down, and adjust the next mixture screw the same way. Continue this until you run out of mixture screws to adjust.
Catpealer's got it right.
Just remember that these are idle adjustments, once you're off idle they no longer count.0
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