One pipe is cold - RESOLVED

Hi,

I discovered last night my newly acquired 82 XJ650 Maxim is not firing on one cylinder (#2 or #3), whichever is the 2nd in from the shift side. There's truly no firing going on.

Pulled the plug and it had a thin layer of oil on it & was black. Checked the wire & there is a healthy spark. Replaced the plug with a new plug and it still did not fire.

I don't have a compression tester here in CT, it's still out in Indiana but even with poor compression there would be some ignition with a healthy spark & new plug.

I do have the service manual & am awaiting the CD but would like to see if I can find/fix the problem myself. Don't want to go to a dealer with it unless I am at wits end. Don't know anyone around S.E. CT I'd want to take it to. This is my first bike in 35 years so I'm pretty much on my own.

Ideas?

Thanks,

Gary

 

Re: One pipe is cold

I'd swap that wire with the other wire the coil feeds just to double check both HT leads. If the problem swaps - the lead/cap is at fault. If the problem does not swap then look at fuel/carb.

 

Re: One pipe is cold

I've tested a plug by holding it against the block while plugged in, hitting the starter. CAREFULLY, of course.

Are you sure it was oil and not gasoline? Oil would suggest a leak, piston rings? I guess a compression test would answer that, once you get the equipment back. If it were gas, a second of WOT while starting would help dry the cylinder.

Might also check the elbow point of the plug boot. A broken circuit there might produce misleading test.

 

Re: One pipe is cold

Hi,

Funny you should ask that. At first I expected gas was the cause of the wet but it was jet black & wet so I thought oil. Didn't smell much like gas but there's a scent of gas in the shed anyway.

With a piece of paper towel I tried digging into the inner cup of the plug between the ceramic center cone and the metal wall to dig out any grease but nada, just some dark wet spots showed but very little of them. I looked at the plug today and it's definitely carboned, that's what gave me the idea that it was oil. Might be oil but not a geyser's worth. Might be gas but not enough to burn.

As to the spark, It's plenty, I definitely saw a good spark from the wire when I put a screwdriver into the connector & brought it near metal to generate a spark. Since I put in a new NGK Iridium plug and there was still no heat generated from that cylinder after running the engine again, it's got to be the carb or at least the fuel delivery for that cylinder being interrupted; if there were any gas in there with a new plug, it would have heated up the pipe & it didn't.

I suppose I need to remove the bank of carbs and see what I can do towards cleaning that one and getting it to run properly. I looked around here (S.E. Connecticut) for anywhere with a carb rebuild kit available but none are in any of the shops here, I'll have to order them mail order.

So I'm going to have to try and figure out what is bad if anything and get it working. I bought some seafoam & perhaps that'll loosen up whatever is bound up or plugged in that one problematic carb. I just don't see how to loosen up what's the problem unless I remove the bank of carbs.

Looked for a can of compressed air but difluroethane at Staples is all I found and I don't want to squirt a rubber drying agent into those old carbs.

This'll be a first for me. Wish there was someone I knew locally with the experience but I'm going to have to wing it.

Thanks,

Gary

 

It turns out the #40 jet in the carb was missing. I was told by the PO that carb work had been done on it & I was suspect seeing as the PO's son was to be the user of this bike & one of his "carb savy friends" had rebuilt the carbs...

I opened the float bowlit was not in the bottom of the bowl, just a big old gap where it was supposed to be. When I finally removed the float itself, there it was; wedged between the float bowl & the upper body of the carb.

Ain't no way that #2 carb was going to work with that going on. So I've got the carbs disassembled and having them ultrasound cleaned tomorrow and I'll see how well they work at that time. Probably will be just fine now the missing parts are going to be back in place.

Going to make the pistons go thunk too...

Gary

 

Thunk won't work, they have to go CLUNK