SLEEPLESS IN VENICE Low compression in KZ900 all 4

Hi GUYS,

My trusty Kz 900 is ill. It will not idle correctly (carbs rebuilt) , backfires, no power, and afterfire. I installed Wired by George's coil fix and it starts better but still runs like sh**. Compression is 110 to 115 in all cylinders. If I add a teaspoon of oil to the plug port the compresion climbs to 160 plus. What seems odd though is that the bike only has 9500 miles. How could the rings be bad and why all of the cylinders reading about the same.??? Thanks in advance for the help.

Sleepless in Florida,
Jerry

did you have throttle wide open when checking compression???? if not you wont get correct readings.....dont add oil doing it.

I'd be checking the Intake Manifolds for leaks, and the Ignition Advance Springs behind the Points cover to start. But we're taking your word that the Carburetors are actually clean.

Yes. Throttle wide open. I also checked the compression with
a hot engine. It only jumped up approx 5 lbs per cylinder.
Thanks,
Jerry

Thanks Kraz,

Carbs were professionally rebuilt last year . I was hoping that was the issue and had them rebuilt just because they have been untouched for some many years. Still ran crappy.
I also installed new points, plugs, coils, wires plus George's fix.. I have the point dwell set at 22 Deg per set and timing was done with a strobe. I added some Seafoam to the crankcase and fuel tank.
Thanks a bunch for your time,
Jerry

Hey Jerry, I have KZ900 with pretty much the 115 psi all the way across. I n the Z series service manual I got here from KZR, it states the standard compression is 121 psi with a service limit of 95 psi. I think my Clymer which is not modal specific states 130 psi or something like that. As long as you are with 14 psi from the highest to the lowest cylinder I would say you are o.k. I have never been able to find out what exact compression is supposed for our model, I even asked here with now response. My bike seemed to have pleanty of power. I would say check your valve clearance first and go from there. Are your carbs balanced? Are they jetted properly for your current setup? Anyhow, which part of Fl do you hail? I'm in Citrus county myself. Good luck.

What are you using for air filtration? Ed

Thanks KZJoe and 650 Ed,


Joe,

Hopefully our fellow KZ folks will clarify the compression issue. I live in Venice.

Ed,
Stock filter system, but I have the filter out while working/testing things. Do you think I should install the filter/airhorn before test rides ?

jerry chabino wrote: Thanks KZJoe and 650 Ed,


Joe,

Hopefully our fellow KZ folks will clarify the compression issue. I live in Venice.

Ed,
Stock filter system, but I have the filter out while working/testing things. Do you think I should install the filter/airhorn before test rides ?

Absolutely. KZ engines run poorly if the air filtration and jetting don't match, so with no filter, horn, etc. your engine will very likely not run right. Ed

Thanks Ed. I will give it a try and provide feedback

Ed,

Installed everything, no change

1. Check Valve Clearances
2. Check Ignition Timing/Points Condition
3. Check Spark Quality

If the problem isn't found at that point:

1. Leak Down Test