i need help tunning dual holly 600 cfm carburetors we can't get them adjusted right so the car will idle. we baught power valve block off plugs to see if we could get it running a little bit better and we still can't get it to idle if anyone can help me on how to tune both carbs so they will run i would appreciate it.
Kinda hard to diagnose what your problem is with so little info. Removing the powervalves wasn't the answer.
is this motor a 302? dual 600s is about twice as much cfm as most 302s will use. if the timeing is too advanced you will never get it to idle below 1000 rpm. i suspect youve backed the idle screws all the way down so the throttle blades are fully closed? chances are the 4 idle circuts in the two carbs are too big for your motor to idle below 1000 rpm.
Carbs being too large usually do not cause idle problems. Since you can correct mixtures with the idle screws. I do believe that your going to have other issues once you get it to idle. Which usually ends up having back firing through the exhaust on deaccelerations from being too lean due to not having a strong enough air velocity. If you correct this then you end up being to rich at other ends. The best way to run 2 carbs that are too big is to get carbs with changeable venturis and run smaller venturis. I just went through this problem on my V12 miata. I fought the problems for 4 months until I went with smaller venturis and 90% of problems were solved. Idle circuits are fairly simple but as mentioned were all guessing until you give us more info or a photo of the details. By the way make sure you put the power valves back in
To get it running close down the rear carb and try to get it to idle on the front carb. After that you can work on getting the second carb on line as you tune them both. You will have to decrease the idle on the front carb as you increase the idle on the second carb to keep the engine speed the same as you include the second carb. Two carbs are in no way a benefit on a 302 or even a 351. there is no way that either engine can use more than 800 cfm unless you have an engine that idles at 2500 and turns into the 10000 rpm range. It make look "cool" to have two carbs but it quickly becomes a nightmare to drive.
