Xj650 dies under load

First time poster long time reader. I have a 1983 XJ650. It sat for a few years and I just went through the carbs. Starts great and idles perfect. I’ve risen it a few times in the past couple weeks and have not had an issue. Today I start it and it idles fine and will rev up in neutral. Put in gear and try to ride it and it Boggs down and dies. I had to feather the clutch and rev it up to 4000 or 5000 rpm just to get it back home. I don’t know if it is related but the clutch cable popped out of the housing the other day on me and I had to ride home less than a mile without a clutch. Thanks guys.

1983 XJ650
Frankfort Kentucky

 

Fresh fuel in it?
My generator and lawn mower experience this issue since both get used rarely.

 

If you'd just put the carbs back on and had these symptoms, I'd suspect plugged pilot circuits. I'm sure you've seen and read the church of clean article and are aware of the procedure. But if it ran fine, then suddenly symptoms begin, it might be fuel delivery. Some gunk from the tank might have finally plugged the in-tank petcock screen, the petcock itself, or the screens under each float needle.

A few simple tests...take the fuel hose loose off the petcock and switch to Prime. Good steady flow? Then also reconnect the petcock, pull your bowl drain screws and switch to Prime again after the bowls are empty, check for steady flow from the bowl drains. And a third step, if you have a vacuum pump, like from a brake bleeder, connect that to your petcock vacuum to check fuel flow in the petcock ON position. Only 5-10" Hg needed, and you can also confirm that the pressure holds and doesn't leak down (indicating a bad diaphragm in the vacuum shutoff).

Or also switch the petcock to Prime instead of ON when running, and see if that changes the symptoms, as an alternative to the vacuum pump check.

 

I had the chance to mess with it a little bit today. Need to get the multimeter out to verify but pulled the plug wires off the left side and no change. If I pull the right side off it wants to die. Could this be a coil issue? Like I said it runs fine in neutral and will rev to 6k rpm with no issue. It’s only in gear trying to move that it has a problem. Thank you guys for the reply.

 

If the plugs aren't firing then that's definitely where to start. But what you described might be spark and might be fuel. You have two coils, left and right. The cylinders are #1 through #4, starting from the left hand side of the bike. The left coil fires #1 & #4 cylinders, so your two outside ones. Right hand coil fires #2 & #3, the inside ones. Each pair of plugs always fires together, so there's an extra spark at the top of the exhaust stroke. If you have a bad coil, those cylinder pairs will lose spark together, which doesn't sound like what you found pulling wires, unless I'm reading your description incorrectly. Still sounds like a lean fuel description above. Or try your plug wire pulling again and check if one of those pairs is both down. Or get a spare spark plug and lay it on the head to visually check for spark.

If only one cylinder isn't firing, say #1, that could be fouled plug, valve adjustment, compression or fuel delivery for that cylinder alone (or occasionally a bad plug wire). And since your symptoms seemingly went from good to bad instantly, compression and valve adjustment are unlikely culprits.

Touching each exhaust header individually is a quick way to check if each is firing...quick being the key word, they'll burn ya! Sometimes a cylinder may not fire at idle, especially if the choke circuit in that cylinder is plugged. Until the 4 carbs are properly synched, you can get erratic firing also. Did you synch after carb cleaning and reinstall?

Running under load will cover many sins of idle circuit and synching, so you can do the burnt hand test cold with choke, warm at idle, or after running under load and get different results.

Fuel, air, spark, compression. The 4 simple things that make it all work. Of those, air, spark and compression are relatively YES or NO. Fuel is the one that can drive you nuts, especially with 4 carbs.

One other simple thing, fill the tank up.

All these suggestions are based around the bike running well, and then suddenly not. If you'd just rebuilt the carbs and had these symptoms immediately, its an entirely different conversation.

 

Thank you for the detailed response. I got my multimeter out this afternoon. The coil is testing good ish. Probably should be replaced soon. But good none the less. Also got my spark tester out and spark on all cylinders looks good. Just took it out for a test ride and rode it pretty hard for 45 minutes or so. Can’t recreate the issue again. I did clean the petcock and made sure it was on. I’m think I was trying to ride the other morning with it in prime. I may have had a brain fart thinking pri was primary.