2 cyl misfire, oil on spark, valve shims?

Hi all,

I'm about to do the valve shim adjustment on a XJ750RJC Seca with 30,000 K. The PO probably never did them. The bike will go around the block but it's gutless. #2 cylinder isn't firing and is cool to the touch after I take it around the block. #1, 3, and 4 get hot. Changed #2 spark plug and it has some oil on it after I take it around the block.

My question is, will a shim adjustment likely fix this problem or has the PO messed up a valve spring?

Thanks a lot,

Aaron.

 

You need to service the carbs after you get the valves in spec. A cylinder not firing could be carbs or spark problems. Is there spark on #2 cylinder? Correcting out of spec valves won't fix a oil problem. A proper burning cylinder should keep the oil. How much are we talking about?

 

Is it oil or fuel?

A non-running cylinder that is getting fuel will have a wet plug.

If it is actually oil it could be a ring problem also. Have you done a compression check?

 

Checking the valves may not fix it, but it will give you the information to move onward.

 

Stop running it before you hurt it.

Get the valves in spec. Do a compression test.

Oil on a plug might indicate a bad valve stem seal, I doubt a valve spring has been compromised.

Quickest guess is that the carbs need to be properly serviced and adjusted. But you need the valves in spec for that anyway, and the subsequent compession test will reveal a lot about the motor.

Dont guess. Proceed logically and diagnose; or you could just make matters worse in the process. You already know it doesn't want to run on all 4; quit trying until you have some idea why.

 

Thank you for the expert feedback and sorry for the late reply. I went ahead and did the valve shim adjustment. Three exhaust valves were out and two intakes. All good now and yes I used new shims.

I did a compression test on #2 and #3 and both were at about 118 to 120. It definitely gets spark. There's some wetness and I suppose it could be fuel but it's dark.

Tomorrow I'm going to hook up my carb gauges and see what that tells me. I did have the carbs off at one point and they looked clean. Do we think removal of the carbs is the next step?

 

Yep.

Followed by disassembly, thorough cleaning, inspection and replacement of all o-rings and any other worn parts; and proper (wet) float level adjustment plus a good precise bench sync.

Do a compression test on all 4 cylinders; you need the data for comparison. It's even easier with the carbs off.

Once the bike is running right, if you're still getting oil in a cylinder, then you'll need to replace the valve stem seals. It can be done without pulling the head, but it employs a rather shaky technique that if it fails, will require pulling the head anyway.

First things first. Carbs. Actually, it's the second thing; but you've already got your valves in spec.

 

Hi all,

I cheated and swapped the entire carb out with a working one and it runs like a top. Good and hard on all four cylinders. Unfortunately I have to put these back but it's good peace of mind knowing we're on the right track. Obviously I have work to do on my carbs. Thanks for all your help.

Cheers,

Aaron.