Compression test

[harmonc]

My 83 is running ok, the right cylinder seems colder and not as hot as the left. I used new jets, 45 and 140 from 650 central-I did a compression test on the right cylinder the one that is running colder than left-I got a consistant 75psi-when I rev'd the engine it went up to 125-is that ok? Whats nexted?

When I sprayed some gas into the intake on the carb the engine rev'd up then idled back down.

Any input?

Thanks Chris

 

[xjwmx]

It shouldn't be running when you do a compression test because you need to have the throttle twisted all the way open. Take both plugs out and ground their threads to something on the bike with clips. Then use the starter to bump it over while you read each cylinder _with the throttle twisted all the way open_. The reading will climb up over several cycles and then stay steady. The steady reading is what you use.

 

[harmonc]

What if it is only kick start? Jusy kick it until it peaks? Why have the throttle wide open?

 

[harmonc]

What is the ok reading?

 

[grizld1]

You open the throttle because the motor is a pump and to have something to compress it has to take something in (air). Factory spec on a warm engine spun at 200 rpm to pressurize is 128-156 lbs. If you get 120 on a cold motor spun with a boot (and right, just keep kicking till the gauge peaks) you're OK.

 

[harmonc]

Thanks,
I did exactly like you said and 3rd kick I had 130 so I stopped.

How do I get more gas to that side of the bike cylinder. I put new jets, cleaned everything. It seems like this side is alot colder that the other. When I sprayed some gas in the colder side the engine picked right up-the plug indicates over rich fuel air mix
Thanks Chris

also waht is the intake and exhaust valve clearance for a xs650 1983, 1982 and 1981
I having a blast

 

[grizld1]

Chris, if you go to www.biker.net you'll find the factory manual free in pdf. Print it off, along with the supplements.

For instructions on carb cleaning and adjustment, go to www.amckayltd.com/carbguide.pdf .

 

[cooltouch]

Actually if your right cylinder were running lean compared to the left, it would be hotter, not colder. A very lean condition can get hot enough to melt a hole in a piston. Now, if the engine isn't running on that cylinder, then of course it will be cooler, but you said the bike was running okay.

Your plug is telling you the truth. That cylinder is getting too much fuel, not 'not enough.'