Well heres a weird problem

Hi folks
I'm still working on my KZ650 to get it running a little faster.

Right now the bike is stock except 110 main jets and a 4-1 pipe.

Last time I pulled the carbs it was to fix a stutter between 5-6K. Heres what I did and heres what happened

1.) Cleaned carbs
2.) Added 3 main jet washers (they were missing)
3.) Checked float height
4.) Added 110 Mains
5.) Replaced pilot jet O-Rings

Results
-Stutter is gone
-Slightly loopy idle
-Accelerates through 1st and 2nd WOT great, but develops a stutter RIGHT after I switch gears
-A stutter is apparent at WOT 3rd gear on...

What now?

Just AFAIK
-Checked for air leaks
-Set valve clearances
-Synchronized carbs
-Extensively checked electrical system
-Plugs are a beautiful brown color
-Did not have this specific problem before I pulled the carbs

Now it sounds to me like a fuel problem, is it possible that the fuel lines running in between the carbs are clogged up? This might help explain why the problem is more apparent at higher speeds (higher fuel consumption). It could also be that the problem only occurs at a specific engine RPM (?) and it is unnoticable 1st-2nd gear WOT because the bike accelerates so quickly through the whole range?

Peter

does sound like low fuel flow to the carbs could be petcock or filters if you have filters

newbikekiller wrote:

Now it sounds to me like a fuel problem, is it possible that the fuel lines running in between the carbs are clogged up? This might help explain why the problem is more apparent at higher speeds (higher fuel consumption). It could also be that the problem only occurs at a specific engine RPM (?) and it is unnoticable 1st-2nd gear WOT because the bike accelerates so quickly through the whole range?

WOT is WOT no matter what the Speedometer says, so if it is a fuel delivery issue, then you should be seeing it as constant on the tachometer. Try running it at WOT in first or second for a while and see if your stutter shows up. If so, then it's time for one more cleaning, this time of the fuel lines, all the way from the petcock to the carb inlet.

...If not... well,.. I don't know. :blink:

It sounds to me like your coils are breaking up.
To see if it's the fuel system, do a plug chop when it happens, if it's fuel related then the plugs will be lighter in color, if it's spark, then they will be darker.
The point at which it is happening (3rd gear, WOT) is the point at which which maximum fuel flow is started, as well as maximum spark is needed, the motor is turning slower at WOT, thus giving it more time to fill the cylinders.
The problem can be caused by a fuel flow restriction, or by the spark breaking down at the higher actual compression, a plug chop when it is happening will tell you.

WOT is WOT no matter what the Speedometer says, so if it is a fuel delivery issue, then you should be seeing it as constant on the tachometer.

When you have the throttle wide open, how long is the motor at 5k rpm in first gear vs third gear?
Keep engine load in mind, the higher the gear, the greater the load, the greater the load, the larger fuel and spark demand.

Post edited by: steell, at: 2006/05/26 09:14

newbikekiller wrote:

1.) Cleaned carbs
2.) Added 3 main jet washers (they were missing)
3.) Checked float height
4.) Added 110 Mains
5.) Replaced pilot jet O-Rings


1. OK... got that part
2. Since there are no washers on the main jets, I am curious as to what this means
3. explain "checked float height"
4. OK... new main jet time - this will not affect idle OR mid-range but what the heck...
5. Since there are no o-rings on the pilot jets, curious about this as well...

Repost this carb related stuff in the carb section if it turns out to be a carb thread.

Since you haven't really tuned the bike up, I am not all that confident your mucking in the carburetors is going to fix your problems. Once you have checked compression, valve clearances, cam timing, igntion timing, the state of health of your coils and cleaned/lubed your igntion advance, we can probably look at the carbs with some degree of certainty that it is worthwhile. As long as you keep fiddling on the wrong end of the problem, there is really no way to be sure it will do any good.

My recommendation is to start working through possible tuning issues in the order suggested by a service manual or Clymer.

Since you haven't really tuned the bike up, I am not all that confident your mucking in the carburetors is going to fix your problems. Once you have checked compression, valve clearances, cam timing, igntion timing, the state of health of your coils and cleaned/lubed your igntion advance, we can probably look at the carbs with some degree of certainty that it is worthwhile. As long as you keep fiddling on the wrong end of the problem, there is really no way to be sure it will do any good.



My recommendation is to start working through possible tuning issues in the order suggested by a service manual or Clymer.

New plugs, wires, checked ign. voltage. Checked timing, checked compression, lubed advancer, checked valve clearances, cam timing, good power to coils.

Should have mentioned I did a full tune up as well as all the other usual things.

Peter