Some time back, my son seriously over revved his Connie.
Cranked the bike and somehow the throttle was open. Tached waaaay up.
Bike had to set as Carbs needed to be gone thru and our enemy (lack of time) raised it's ugly head.

Last week he went thru the carbs. Had some blockages that he cleared out.
Bike now cranks and runs ok, but has a miss. Most evident at high rpm's.
He Replaced plugs, checked the spark plug cables.  (3 plugs look ok, 1 is black and sooty (#4))
1 wire (#3) was pulled partially out of the coil.
I suggested trimming the cable but was not done. Pushed the cable back into place.
Miss is improved, but still there.
No bad mechanical sounds. So I don't think the overrev hurt him. Have not had time to check compression etc..... (Want to see if he bent a valve)

I recall that some have had a problem because of improper gap between the timing plate and the pick up coils. (Not at home so don't recall proper terminology)
What is the correct gap?

Other suggestions??

Ride safe, Ted

PS: I'm not able to be there with him on this project but talking with him on the phone...

Black and sooty, ASSuming it's not oily and/or wet, would lead one to suspect an overly rich condition on the number 4 cylinder, but not enough to flood it totally out. Maybe time to recheck that carbbie for issues.

I had a miss in my 87.  Got progressively worse.  It was the pickup coil gap.  They should be equal but I forget the minimun clearance, like 50/000 or something up to 90. Very easy adjust other than pulling the left side plastic and timing cover/gasket.  I used Permatex Blue so I let sit 12 hrs or so before using so it has a chance to cure more.

When he first put the carbs back on, he had a flooding issue with #4.
The carbs are off a ZX-1000 (38's I think) and I know they need new needles. So you might be right. (that might be it)

I was thinking that a flooding problem would act up at lower rpm's and clear out at WOT. This bike gets worse at WOT. I was suspecting fuel starvation on 1 carb.
I'll get him to check the carbs again, but want to check the Pickup Coil Gap first.

Summit said he thinks it is .050 - .090.
Can someone please confirm?

Thanks for the input!!!


Ride safe, Ted
Ride safe, Ted

If it were the pick up coil, the problem would be common on two cylinders, most likely, as one of 'em works 1&4, the other 2&3. If the problem gets worse with more throttle, needles? main? Simply over carbureted? Could be the float needle is stuck part way? Floods on low fuel draw, starves on heavier use?

I'm not a carbbie magician, so mostly this are guesses that could be.

Good Luck. I'll yield the floor to a real magician.

My 87 pickup coil air gap according to the Kaw Serv manual should be 0.5 - 0.9mm

Pickup coil resistance is need to check is 390-590 ohms

Jim

I agree with SteveJ. It maybe carbs.
 We would know more with a compression check to be sure it is ok mechanically.
Then a float level check which is another easy thing to do..
Swap the spark plug wires with  #1 and #4 and see if the black sooty spark plug issue now occurs on #1. Maybe move that dirty plug to a working cylinder to make sure it is not a defective plug. It happens.
Also check the gaps on  those plugs.  Some are not set correctly and  may have too big of a gap.
That is all I can think of right now.  Vacuum caps are not leaking?
Good luck.

I appreciate the assistance. He has already replaced the plugs.
Sounds like we'll be pulling carbs again.   arghhhhhh

Ride safe, Ted

I agree with SteveJ. It maybe carbs.
 We would know more with a compression check to be sure it is ok mechanically.
Then a float level check which is another easy thing to do..
Swap the spark plug wires with  #1 and #4 and see if the black sooty spark plug issue now occurs on #1. Maybe move that dirty plug to a working cylinder to make sure it is not a defective plug. It happens.
Also check the gaps on  those plugs.  Some are not set correctly and  may have too big of a gap.
That is all I can think of right now.  Vacuum caps are not leaking?
Good luck.

As a newbie to carbs, I have a question. Other than opening the petcock, what function does the vacuum have with the carbs?

As a newbie to carbs, I have a question. Other than opening the petcock, what function does the vacuum have with the carbs?

In an over simple form:

Manifold vacuum provides the lift to open the slides the required amount not the requested amount; hence the term Constant Velocity Carbs or CV.... Your wrist opens the butterfly plates in the back of the carb allowing the air to flow in up to the requested amount and the slides which operate on the diaphragms allow carb to open up to the point that the engine can handle due to inlet manifold vacuum; this is why there is no bog in our engines when you whack open the throttle as you once had on older bikes.

In an over simple form:

Manifold vacuum provides the lift to open the slides the required amount not the requested amount; hence the term Constant Velocity Carbs or CV.... Your wrist opens the butterfly plates in the back of the carb allowing the air to flow in up to the requested amount and the slides which operate on the diaphragms allow carb to open up to the point that the engine can handle due to inlet manifold vacuum; this is why there is no bog in our engines when you whack open the throttle as you once had on older bikes.

Great info T, thanks. I don't really want to do a hi-jack, but this is along the same lines as the op's problem. How much of a vac leak would it take to bog our bikes down? My bike is bogging down at wot. Mainly between 4-55k then it pulls out of it like a monster. I have always thought the vac lines were sloppy on the nipples. It idles and revs great, it just bogs under heavy accel.