Valve broke.so I replaced all 4.and piston rings.wont start no more. low compression 90.put oil in spark plug hole.and compressing when up to 120.valve clearance within spec.cant figure out what's wrong. I will appreciate for your help

Did you orient the rings per the service manual?

The guy at the shop where I had the valve seat redone did it for me.but I don't know what you mean by oriented.can you explain

There are basically 3 Piston rings on each piston - and the gaps of the rings are supposed to be spaced out 120° from each other. Speaking of ring gap......they may be spaced out to far (out of spec).

Since you went from 90 psi to 120 psi, it shows that the piston rings are part of the problem. But your valves might very well be a factor too. Were the seats lapped with the valves when they were installed?

Honestly man, you really should take it back to the shop and explain to them what's going on.

I got the bike running and it was the carburetors.not sinc.and abou the low compression it seems fine when for a ride and it runs strong.but I have one more issue.when I'm shifting gears. idle is to high even when I release throttle.

Quote from: Gmoscajal69 on August 15, 2016, 01:12:42 AM
I got the bike running and it was the carburetors.not sinc.and abou the low compression it seems fine when for a ride and it runs strong.but I have one more issue.when I'm shifting gears. idle is to high even when I release throttle.

have you found the problem? mine does the same. it has low compression, 6 bar per cylinder and idling at 3-4 k when fully wormed up
p.s. valves is in spec. and i've just rebuilt engine too

1. the carburetor adjustment is not going to cause a compression problem. OP's compression numbers look to me like both the rings are not done right and the valves are also not seating correctly. Take it back to the shop and have them fix it. They will have to redo it. I am guessing they really should refer you to another shop. If those compression numbers are accurate on a fresh top end rebuild then it's a sign that they really don't know what they are doing.

Regarding the high idle, you just need to adjust the idle. Big knob facing down between the carbs. See the wiki, tons of information on how to do it. The shop that did the rings & valves should have done this too.

Check valve timing first if both cylinders are that low.

http://img.photobucket.com/albums/v443/jcp8832/gs500signalgenerators_zps6gldzd0e.jpg

+1 on the valve timing 

i'm guessing I've done the compression test incorrectly.
I found out yesterday  that i should have opened the throttle while taking measurement is it right?

Yes, hold throttle wide open.

And do about 6-8 cycles before taking a reading.

thanks for help. i'm guessing compression will be in spec with open throttle.
shims is in specs i have checked it 10 more times its a strange problem why idle hangs when engine fully worms up.
i had this problem 1 years ago and it was tight exhaust valve. but now after rebuild i have no idea whats causing the problem.
i even replaced that shim just in case

Quote from: system32 on November 01, 2016, 07:11:39 AM
thanks for help. i'm guessing compression will be in spec with open throttle.
shims is in specs i have checked it 10 more times its a strange problem why idle hangs when engine fully worms up.
i had this problem 1 years ago and it was tight exhaust valve. but now after rebuild i have no idea whats causing the problem.
i even replaced that shim just in case

Is it a hanging idle (revs up fine, but stays high for a bit then eventually drops back down on its own) or a high idle (revs up, then drops to a certain point and stays there indefinitely)?

The former means you are running lean, the latter means you need to adjust your idle screw.

it's  hanging idle revs up fine, but stays high for a bit then eventually drops back down on its own.
today i checked the compression with open throttle but no difference, i was still 6bar (87psi) on both cylinders.
that i added the oil in it and it went up to 8bar (116psi) on both cylinders.
the guys who repaired my engine has polished all valves and said that the rings were in good shape. 
what do you think guys?
many thanks for help

116 is very low. 150-160 plus is a typical figure for an engine in good condition. Are you sure the guage is accurate?

Rings, worn bore/piston, valves not seating, incorrect valve gap, timing, cracked head/seat 

Without opening it up and taking a good look its impossible to be specific. I would take it back to your man and ask him to explain.

Have you checked valve timing?

Quote from: system32 on November 06, 2016, 01:19:44 PM
it's  hanging idle revs up fine, but stays high for a bit then eventually drops back down on its own.
...

Your engine is probably running lean, as hanging idle is normally a symptom of a lean condition. I would maybe adjust your mixture in your carbs.

However, if your're getting low compression, I would probably try to rectify that first as that's the more serious of the 2 problems.

Quote from: qcbaker on November 07, 2016, 06:57:22 AM
Your engine is probably running lean, as hanging idle is normally a symptom of a lean condition. I would maybe adjust your mixture in your carbs.

However, if your're getting low compression, I would probably try to rectify that first as that's the more serious of the 2 problems.

Low compression can cause the hanging idle regardless of idle mixture. It's a waste of time and counterproductive to try and adjust the carbs when the compression is this low.

Fix the big rocks first. Take the bike back to the mechanic who did the head/rings work and get them to make it right.

Quote from: mr72 on November 07, 2016, 07:20:34 AM

Quote from: qcbaker on November 07, 2016, 06:57:22 AM
Your engine is probably running lean, as hanging idle is normally a symptom of a lean condition. I would maybe adjust your mixture in your carbs.

However, if your're getting low compression, I would probably try to rectify that first as that's the more serious of the 2 problems.

Low compression can cause the hanging idle regardless of idle mixture. It's a waste of time and counterproductive to try and adjust the carbs when the compression is this low.

Fix the big rocks first. Take the bike back to the mechanic who did the head/rings work and get them to make it right.

Didn't know low compression could cause hanging idle as well. Interesting.

Anyway, yeah that's definitely the thing you should try to get fixed first, OP. Then, circle back to the other issues if they persist.