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Cylinder 3 not sacking in as hard as others

  • Thread starter Thread starter Redbeard
  • Start date Start date
R

Redbeard

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Hey I have a 1981 gs1000 and it wasn't starting so I decided to take off the carbs to make sure air was actually being sacked in the cylinder and the 3Rd one didn't have the same power as the other three. What could cause that problem?
 
Tight valves if you're lucky. Burnt valves from running too tight too long if you're unlucky.
Maintenance is a beautiful thing.
 
Dang how would I get around the figuring if in lucky or not. Haha. And what would be the best way to fixing it.
 
Well charged battery and spark plugs removed run a compression test on all 4. If one or more are lower than others by more than 10%, then a leak down test is warranted to see where the problem lies. That will point to the problem but since these old bikes require periodic maintenance and known to have the valve lash go narrow you might as well start there. Then run compression test and leak down to further troubleshoot.
 
First if you are not familiar with how a overhead camshaft engine works i suggest you watch this video (it will make diagnosis easier) https://www.youtube.com/watch?v=zA_19bHxEYg

Second.


1: Pull the spark plugs on all cylinders
2: Pull the valve cover
3: Get a compression tester (you can usually rent them for free at auto zone)
4: Perform a compression test on all 4 cylinders follow this (https://www.youtube.com/watch?v=X_tbksFYhl4)
5: Post results


what you can do with cylinder number three for a basic test....
when the cam lobes are not touching the top of the shim on cyl 3.... find an air tool like this (http://www.xtremediesel.com/viairbl...tzjNB-oc7pT9uefU9rv8J2HOy1_aILIK_txoCba_w_wcB)

now blow air into the hole where the spark plug was.... if you hear air rushing out either the intake or exhaust you have a problem....

there could be 3 potential problems....

A: Valve shim is incorrect (what ive been going through for the past couple of days), the cam is resting on the top of the shim and wont allow the valve to fully close, and will cause a HUGE air leak (its what burnt the original exhaust valve i had in there)
B: Burnt Valve.... requires a head job
C: Worn compression rings, and or worn cylinder (worst case)


here is how to perform what i said above... many call it the leak down test, but my method is a little more.... redneck


this is the proper way
https://www.youtube.com/watch?v=WgrfT0LFMhc
 
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I like Eric the car guy and watch his videos often. Maybe I missed it but to run a leak down test, that cylinder has to be at TDC on the compression stroke, for meaningful results.
 
Shim adjust valves tighten up with wear to the point they stick opened. Adjust your valves before wasting time with compression tests.
 
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