RPMS slowly drop after blip of throttle

Hello all,

I have a 1980 kz650 f1. VM24's w/pump accel. Gravity fed Petcock.

Recently had trouble with cylinder 1&4 cutting in and out. So I replaced my old Kawasaki electronic ignition with a brand new Dyna S. Already had Dyna 3ohm coils on it. After installing and timing the ignition (which I'm not sure I did 100% correct). I got it running on all 4 cylinders. Runs like a bat out of hell. I was able to get correct timing on cyl 1&4, (12v test light went on as furthest right advancer mark lined up with engine case), but there were not any "T" or "F" marks on the advancer for cyl 2&3. So I did not adjust that module.

However, my problem is now that everytime I get the bike to a nice idle and blip the throttle, it surges like crazy and hangs to the top RPM I've reached then will slowly go down to a very poor-barely running idle. It will hesitate on the first blip, then zoom up in RPM's a half second later.

I'm not sure if this is a carb problem, which is possible, I did rebuild them. But it wasn't doing this before the whole ignition problem.

Also I checked for vacuum leaks by spraying carb cleaner while it idled and it surged in power as I did that. I made sure all clamps on the boots and vacuum lines were tight, but still had the same problem when I sprayed near any vaccum connection. The vacuum lines looked to be in decent shape (no dry rot or obvious holes). Also carb boots look pretty solid. I did replace them not long ago(but I'm not ruling that out either).

My question is, could timing be an issue here? I don't feel super confident that I did it 100% correctly. Or does this seem like bad fuel air mix with something like the vacuum lines, or float levels.

Close the pilot air screw half a turn and try again. Seems the pilot circuit is lean... that is way the rpm hang and drop down really slowly.

Thanks for getting back so quick.

Just adjusted the pilot screws half turn in. That seemed to get rid of the hesitation, and rpm's seem to drop faster, but still hanging for longer than they should. What is the pilot screws normally adjusted to in ball park range? I had them 1 1/2 turns out, now they are a full turn out. I have stock airbox and stock exhaust. 97.5 main jets if that helps.

Thanks
Jared

If it surged when you sprayed the carb cleaner, then it sounds like you have a Vacuum leak in the area where you sprayed & It surged, It's hard to see cracks in the rubber !!
Pete

Your carb holders are leaking. The symptoms you describe are classic carb holder vacuum leakage symptoms, and the fact that spraying carb cleaner around the holders affect the idle proves that is the problem. Carb holder can look perfect, but still leak because the leakage occurs through tiny hairline cracks on the holder/cylinder head mating surfaces. These cracks cannot be seen with the holders mounted on the engine. Ed

Just took it for a quick spin. It actually really helped a lot when adjusting the pilot.I guess having the bike under load helps bring the rpms down. However when I am stopped and idling the bike still feels like it doesn't wants to deccel like it should.

Looks like everything else is good besides the carb boots. I'll be ordering a set of those and new vacuum lines.