CB650 cylinder 3 not firing like it should

[scottyfunj]

I recently cleaned and synced my carbs and got my new project cb650 running, but cylinder 3 isn't producing heat like the other 3 are. The exhaust pipe stays much cooler than the others when I run it (it does warm up a little, but there is an obvious difference when compared to the others). The spark plugs look relatively clean, but I'm not ruling out the possibility of just having a bad plug. I'm just curious as to which things I should check first. Spark plug wires maybe? I just don't want to get too far into fixing something only to realize that I'm not fixing the problem.

Any advice would be appreciated.

 

[620dark]

Yea, I'd check the plug wires - you might just want to go get some bulk plug wire from the auto parts store and replace the 30+ year old wire to be on the safe side. Check the resistance in the spark plug caps as well - should be about 5k ohms. I had one that was infinite resistance - that was an issue.

 

[scottyfunj]

Thanks, I'll give that a shot.

 

[JohnnyCB650]

Switch the plug wires between 2 & 3, then the resistor caps, then the plugs. If cyl 2 stays cold after any one of these then you've found the culprit and replace as necessary (if the wires, caps, plugs are old it wouldn't hurt to replace them all anyway). If not, then check valve clearances and if that doesn't work, I'd suspect a carb issue.

 

[scottyfunj]

Good idea. I'll try that first. Thanks!

 

[scottyfunj]

Ok, so I tried switching plugs, wires, and resistor caps between cylinders and nothing changed. Cylinder 3 is still the problem. Any recommendations for what I should try next? Check valves maybe? If it's a carb issue, what would it likely be? I appreciate any help in advance.

 

[620dark]

You can try opening the drain screw in the float bowl to see if you are even getting gas to #3. Checking valves is a good idea too.

Have you cleaned the carbs yet? You might have a clogged jet or you might not be getting fuel into the float bowl.