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Low compression on my 1980 kz250 LTD

  • Buschpush
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25 Jun 2024 16:08 #901330 by Buschpush
Low compression on my 1980 kz250 LTD was created by Buschpush
I'm having low compression issues with my KZ 250 LTD from 1980. I just redid every gasket Head gasket side gaskets everyone you can think of new o-rings where could I be losing compression? I'm really stomped and it's got me bummed It's sitting at 70psi is it because I didn't torque down every screw but only some of them? I also didn't replace the piston rings.

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25 Jun 2024 17:45 #901335 by TexasKZ
Replied by TexasKZ on topic Low compression on my 1980 kz250 LTD
Are you measuring the pressure on a fully warmed up engine with the throttle wide open?
Is the release valve on your gauge near the cylinder or near the gauge?

1982 KZ1000 LTD parts donor
1981 KZ1000 LTD awaiting resurrection
2000 ZRX1100 not ridden enough

www.kzrider.com/11-projects/620336-anoth...uild-thread?start=24

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  • Buschpush
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25 Jun 2024 18:02 #901338 by Buschpush
Replied by Buschpush on topic Low compression on my 1980 kz250 LTD
I can't get the engine to start triple checked timing triple checked valve lash, starts occasionally but currently can't get it running again I'm assuming it's cause of low compression. Am I wrong?

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  • Scirocco
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25 Jun 2024 18:09 #901339 by Scirocco
Replied by Scirocco on topic Low compression on my 1980 kz250 LTD
A leak down test @ TDC tell you the truth about leaking valves.

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25 Jun 2024 18:21 #901340 by chopper1963
Replied by chopper1963 on topic Low compression on my 1980 kz250 LTD
A compression test would tell you a lot. There are cheap ones on eBay now.

I bought a set at a garage sale for $3 last week.

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25 Jun 2024 18:22 #901342 by TexasKZ
Replied by TexasKZ on topic Low compression on my 1980 kz250 LTD
The reading on a cold engine will be quite low, and not having the throttle open will lower the reading quite a bit more. Also, a gauge with the release valve next to the gauge instead of near the other end of the hose will give a slightly lower reading. The combination of these things can give a very low reading.

I think the general consensus is a reading near 100psi is required. The most likely leaks are past the rings or past badly burnt valves. The easiest way to find out is the leakdown test Scirocco mentioned.

I have never tried it, but I have read that a hillbilly leakdown test can be made by connecting an air hose into the spark plug hlole and applying some air pressure, insuring that the valves are closed. Listen carefully at the end of the muffler, at the crankcase vent, and at the carb to listen for hissing.

1982 KZ1000 LTD parts donor
1981 KZ1000 LTD awaiting resurrection
2000 ZRX1100 not ridden enough

www.kzrider.com/11-projects/620336-anoth...uild-thread?start=24

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  • Buschpush
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25 Jun 2024 19:41 #901346 by Buschpush
Replied by Buschpush on topic Low compression on my 1980 kz250 LTD
Thankyou so much man doing this tomorrow 

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25 Jun 2024 22:59 #901350 by Wookie58
Replied by Wookie58 on topic Low compression on my 1980 kz250 LTD
I'm confused, in last month's thread on the same topic you started at 90psi which improved to 110psi when tested with the throttle open. What has changed for the situation to have worsened ??????

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26 Jun 2024 00:50 #901352 by Buschpush
Replied by Buschpush on topic Low compression on my 1980 kz250 LTD
I tested on a different compression tester and your right it's at 110 I used my friends to double check and it seems he had a broken one.

My mistake brother

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26 Jun 2024 00:59 #901354 by Wookie58
Replied by Wookie58 on topic Low compression on my 1980 kz250 LTD

I tested on a different compression tester and your right it's at 110 I used my friends to double check and it seems he had a broken one.

My mistake brother
110psi should be enough for it to start, I think your starting issue lays elsewhere

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