Help needed - 1983 KZ750 L3

Claude. wrote:

Injected wrote:

You should go back and check the basics (fuel, compression, spark, timing)

Are the plugs wet? (fuel) What is the compression on all 4?

If you have a OEM Kawasaki electronic ignition the Igniter box can often be the issue putting out weak spark (happened to me) - there are ways to check the spark output.

Sounds like you have a vacuum leak somewhere (negative spray test)

Plugs are wet but #2 and #3 seems darker.
I took compression in january and it was not so bad. From memory, 3 cylinders were at at about 135 psi and one closer to 120 psi.
Thanks!


 

5 month old compression numbers?? Hot or cold?

Seems low for that engine according to FSM. Low compression makes for cold pipes (dropping cylinders) weak spark is also a culprit. You want to be in around 160-180PSI or more hot, these small motors don't run very well at 120-130PSI.

 

Injected wrote:

5 month old compression numbers?? Hot or cold?

Seems low for that engine according to FSM. Low compression makes for cold pipes (dropping cylinders) weak spark is also a culprit. You want to be in around 160-180PSI or more hot, these small motors don't run very well at 120-130PSI.
 

Yes, 5 months old compression numbers. But the engine did not run since then as it have been on my work table since about last november. In fact, this engine did not run in about the last 20 years. So, number are for a cold engine.
I will take compression again this week.

Just took compression. Cold engine, no spark plugs, no carbs and no carb-to-head rubbers.
#1 = 155 PSI
#2 = 135 PSI
#3 = 140 PSI
#4 = 150 PSI
A bit low but surely acceptable (?).

Spray start gas around the inlet rubber, if the engine change sound, you have a vaccum leak?

Gordone, as I originally wrote, I already did this. New carb-to-head rubbers are already ordered. Thanks!

Claude. wrote:

Gordone, as I originally wrote, I already did this. New carb-to-head rubbers are already ordered. Thanks!

sorry

Finally received and installed new carb-to-head rubber adaptors. Looks like the engine now turns pretty well!!
I'll have to ride a a bit in the small streets around the house to be sure everything is OK. If it is, this bike will be for sale!

At first, because of the condition of the OEM rubbers (they had no cracks and were still softish), I was quite skeptical. I now know I can't underestimate the experience of you guys!! Many thanks for your help!!

Short ride taken this afternoon and I confirm the bike works great!!
Thanks again!