1987 140 Looper spit back/mis-fire at idle. Any guesses as to why? Anything typical to these motors?

Waking up a 140 1987 looper from a 6 year slumber.

Previous owner is a friend and a mechanic . Started right up, but seemed to idle too high. Had to lower idle timing to go lower - which is odd given the motor was setup properly when moth balled.

As a precaution rebuilt carbs (they were spotless) with 4 new mallory kits. Replaced plugs, wires and inspected cylinders - They looked pretty good and linked and sync..

Compression is 125 123 126 114. Not perfect, but solid. I can recheck if necessary.

Idles fine down to 1,000rpm when going lower - at some point - it mis-fires. Seems to give off a puff of smoke when it mis-fires.

I have tried to isolate by pulling individual plugs, checking timing changes when it happens, pulling plugs, nothing obvious.

Plugs have sometimes been wet(seems to change a bit).

Tried checking the re-circ system and it seems fairly decent - without being able to compare to new parts it's possible things aren't as free flowing as new.

No vro, fuel pumps works well. Sprayed motor for intake leak - nothing.

Have factory manual.

Any help would be appreciated.

Thanks for the quick reply.

I did the carbs with a new kit and needle and seat. I blew out all the passages with cleaner and air hose although they were spotless to start. I did not remove the throttle bodies only the carb bodies.

I did put a timing light on it and the mis-fire did not show spark related.

Plugs are somewhat oily and it is very smoky especially when you rev it up. That may due to an over abundance of an oil/seafoam/quicksilver concoction. Before I started the motor I had motor tilted up and individually soaked the cylinders with plenty of the stuff (24 hrs each). Maybe 2 ounces or so, each. Had pistons at TDC and by the next day all was gone from cylinder. Moved on to next cylinder.

I did hook up a clear siphon to the lowest crank drain fitting and nothing came out.

I've had it running in a barrel cowl off for about 20 minutes total at mostly 1-2k rpm.

It's tough to pin point any one cylinder. I had it idle as low as 500 rpms on 3 cyl and switched it around, but at some point it seems to misfire with all combo's.

When I pulled the lower unit, I used the push back method you had described in a previous post and could hear the phoosh that you mentioned - they seemed ok.

Carbs are closed. I'll check the primer.

I've already had the heads off and planed and the one cylinder that's a little lower has one score line that the others didn't. I've seen way worse with running motors. I cleaned it up with a little scotch bright.

I have a complete 2nd 140 if I need to swap any parts.

Thanks again,

I circled back with what you said on ensuring the throttle are all completely closed. They looked great but I disconnected all the linkages and it smoothed everything out. I then advanced the idle timing a bit (it was at ~14degATDC and it now runs pretty darn good.

I think the idle timing got crazy, because a throttle(s) was a tiny bit open and I had to retard the timing like crazy to get the RPM's down.

11deg gives about 700rpm and 8deg gives me about 875rpm neutral as it's barely in a barrel.

There's a barely perceptible amount of spit back on the lower 2 carbs at slow idle, so that's what is next to tackle.

I put a light sheet of paper at the carb opening and it vibrated out and back about a 3/8"+. I recall there should be a light suction on it...so maybe the reeds got a tad rusted from the long hibernation???

I still can't get over how much better this motor is running in a few short hours!!!

Not looking to make it run better, just remove any high spots. As normal service, I replaced both thermostats and diaphragms. Checked temp with infrared gauge.

Not ideal on the one cylinder, but would you junk it? If it was a bit coked up or carb issue, that's fixed.

Any tips on the reeds?

Thanks again.

OK, Thank You!

Check your pickup timing it needs to be right on, your numbers is way off ..Check the manual....