blue thunder

Thats easy enough Rob, I'll try it. Why does it work like that? I thought the vent was to keep the float bowls at atmospheric pressure and for overflow. Does the power valve being blown allow air in through it's diaphram thereby acting as a vent?

Dave

formula31

It sure sounds like that might be the problem. You already answered the first question. If the throttle plate is open too far at idle, the idle mixture screws have little effect. If the power valve doesnt solve the problem. If the one engine is OK with the same type and size carb, you should find the problem with this carb before starting to modify it. Assuming it is the carb. You could always put it on the other motor and try it. See if the problem happens over there too.

blue thunder

I rebuilt both carbs F31 and set them up identical. Both engine idle well. The other engine smoothed out at 15"hg and about 2 turns out the the idle screws. This engine smooths out at 15"hg and about 1/4 to 1/2 turn out of the screws. Turning them all the way in doesn't stall the engine. It did on the other engine. I need to get out there and tune some more.

Does a power valve tester by chance work without dissasmbling the carb?

Dave

formula31

Are the throttle plates open the same amount at the same idle rpm?

blue thunder

I'll bet my morse cable is holding it open a tad. More tuning time needed. Any more tuning tips on these holleys? I'd like to find a way to get the same info as plug readings but with a vacuum gage? Is that practical? Taking plug readings suck with a twin engine vessil.

Dave

formula31

Ha, I cant get at mine at all, try doing plug reading when you have to pull a motor. I try and run mine rich just to be safe. I have some stuff I can scan and email to you, just have to find it. Most of my knowledge is on the early 780 cfm 3310's though.