SOHC.co.uk Forums > CB500/550

3 cylinder 550

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mickwinf:
hi guys would like some tips to get my k3 running better. After 28 years in bits the engine now runs, but only on three cyls, no 4 is not firing. I have swapped plugs and checked timing, also opened gap on valves  which seemed to improve matters slightly.New plugs points and coils fitted but only occasional spit back through no 4 carb, if plug lead taken off with engine running it makes no difference.When checked against earth plug has strong spark.Is it likely that it is a valve problem, the head and barrels were rebuilt by po, and i already discovered cam timing was well out!!  Any ideas welcome, thanks,Mick

SteveD CB500K0:
If you have a spark on #4 it sounds like fuel starvation.

Is the plug wet when you remove it?

mickwinf:
steve it dosn't seem that wet when i remove the plug, so i tried squirting carb cleaner in the carb and a bit in the cylinder, expecting it to fire but no luck!

470four:
+1 on fuel starvation... float stuck shut? Pop the bowl off if you can and see if there is any fuel feed to that carb?

z1100r:
what do you mean by cam timing well out. It might have bent a valve if its that far out. Check compression on that cylinder...compare to number 1.

If you haven't got a compression tester take the plugs out and put your thumb over the hole. crank it on the starter motor. Compare the difference between 1 and 4. Should blow your thumb off if OK,  wont do much if you have a bent valve.

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