Drops 2 cylinders when hot?

[buggrin]

Just got a call from the shop that's cleaning the carbs on the 78E. They got it buttoned up with the tank on for another test ride (it took a few test rides to get it right) and it ran great.... until 2 cylinders dropped out after it warmed up. Thinking it might be the coil, they switched coils, and the same 2 cylinders dropped out again after it warmed up. All day troubleshooting has not solved the problem, so they called me (they knew I was the original owner and have only recently quit doing the wrenching myself) looking for guidance. Not exactly the call I was looking forward to.

Well, a good bit of my knowledge (almost all of it) came from this site over the years. I looked at the tips & searched, but have not come up with a probable cause. It sure sounds like an intermittent ignition problem, but how the heat is causing it is beyond me.

Does anyone have any experience and/or ideas on how to fix this? I've been riding this bike since it was new in 78 and it has been very dependable. Now I'm getting worried it does not like someone else playing with it's innards.....

[motoman]

Pick-up coil wires under the left ignition side-cover.......................and yes, don't like anyone younger than they are screwin' with their inards.............

[buggrin]

Thanks for the reply MM. As I can recall (which ain't much) there's never been a stray electron (electrical problem) in the old girl. I mentioned the pick up wires to the shop when he was wrenching on stumble problems in the carbs, but don't know if he checked them at the time. This time he'll get a primer on checking those wires from the info section.

I sure hope it's that simple and not in the regulator (as my pessimistic attitude fears)

[slow mo]

[QUOTE=motoman;342102]Pick-up coil wires under the left ignition side-cover...................
i think that is the answer to your problem ,,side safe ,,slow mo!

[buggrin]

Passed on your observations as well as a copy of the ignition troubleshooting guide. Thank you both. Quick inspection of the wires showed a couple neck-down spots indicating broke copper. Also found a repaired/soldered section (most likely by me) which I have forgotten. Expect misfiring to go away with new wires.

BTW, spent two hours talking to the mechanic -- a youngster (in his 50's) who has a special passion for these old carburated machines. Since I'm not able to do this kind of work any longer it's really nice to find someone like him. When you spend more than 34 years with a machine, the value of having it run ok is different, and saving a few bucks becomes less important

[SUPERDOM 82]

maybe same problem with my xj

Guys been reading what you aren saying and i have same problem maybe after goin 50-65 for 3 miles i lose cylinders i thought it was carbs but maybe not any comment on this? superdom

[DGXSER]

Hi Superdom,

The XJ does not have any of the moving parts in the timing assembly that tend to cause the wires to break, so it is alot less likely, but not out of the question that your XJ has the same problem.

Can you tell which cylinders are missing? 1-2, and then 3-4 are joined together by the fuel system, while 1-4 and then 2-3 are joined together by the electrical system. So if two go out at the same time, you can typically figure out if its fuel or electrical by seeing which pair it is.

If just one cylinder is acting up, then the most likely culprit is carburation. That or the spark plug, plug wire, or plug wire end. Anything beyond that effects more than one cylinder.

[lancelot455]

My xj was doing the same thing dropping two cylinders. i swapped the coils and the problem didn't move. Pretty sure it's the tci and am going to be changing that in the next couple of week. Good thing i have a backup bike.