FricFrac

I just rebuilt my triple Mikuni PHH 44s reinstalled and set the pilot screw to it's original setting of 1.25 turns out from bottom. The butter fly valves are completely closed and it will idle around 1000 RPM(ish) then it will idle right up to 2.5 to 3K RPM after a minute or so. That's with the starters turned off. If I play with the butter fly valve opening (idle set screw) and turn in the pilot screw to about 3/4 it seems to run but its rough. I haven't balanced it out yet. I'm trying to understand what's going on so a little direction on my misunderstandings would be great. My understanding is that the pilot screw adjusts the amount of air added to the mixture. Turn it in - less air. Turn it out - more air. So the part that confuses me is if I turn it in to 3/4 and open the butter fly valves it seems to run better. I can understand that the air is metered differently through the pilot screw adjustment than the butter fly valve but that would be at various RPMs. Shouldn't it be the same at idle?

I rebuilt the carbs completely but I was told not to mess with the throttle plates and shafts so I never replaced the shaft seals. I'm assuming air could be leaking past the shaft but it never did before and I would think it would have to be a significant leak to go from 1000 RPM to 3000 RPM.

Thanks guys any help is always appreciated! I'm dying to get this back on the road. The plan was to have it ready at the begining of the summer but I kept doing the "while I'm at it" lol.

the_journeyman

Generally with carbs, a racing idle is often an air leak between the carb & intake valves. The backyard mechanic method of finding it is to spray a bit of WD40 or carb cleaner at a suspect spot and see if it causes more of an RPM increase.

I have Mikunis too, but have the opposite problem. It will idle, but left sitting, it eventually slows idle until it stalls.

JM