Can't get the gremlins out!?!

Picked up a used 81 xj650 for 500 bucks. Seems to run fine and then all of a sudden it will shut completely off. If I coast in gear it still won't fire. The second I stop and put it in neutral it fires right up again and goes for another KM or 2 and does the same thing. After about 2-5 times of doing this it seems to run fine. I pulled the tank and checked that the vaccum operated fuel valve is working (and it is,) also does it even when it's set on prime so I don't think it's a fuel issue. Is there something in the power system that could be causing this? I thought maybe the power was shutting off but it seems to not be, when it happens in the driveway in neutral the neutral light stays on. Plugs look fine. Pulling out my hair trying to figure this one out, not fun when it happens at a stop sign! Cheers.

 

Double check your gas cap and see if the check ball is all gunked up for the vent. No air going into the tank will starve the carbs for fuel.
Next time it happens , pull over and open the cap and try to start it. If it goes your gas cap is in need of cleaning.

 

Yes I suspected as much too, tried riding it with the cap half latched and it still does it :-(. Also was able to open the valve and drain the whole tank with the cap tight so it's not that. I'm thinking maybe something in the kill switch circuit? Going to check that out tonight. Thanks for the input!

 

I am going to take apart the gas cap and clean it just to make 100% sure.

 

Sounds like something going on with your side stand safety circuit, which is maybe why it won't restart till you get it into neutral.

 

Ok great
How about bringing a spare plug and pop it in quick when it kills to get a visual if there is no spark.
If no spark I would look at your module for broken solider joints.
I had one do that and it was driving me crazy.
Also check all of your ignition switch connectors in the headlight. Remember those connectors are cheap brass and like to turn green and crack.

 

Bingo.
First place to look for the random ignition cutout issue. Remove the rubber boot and clean the switch with contact cleaner (moving the plunger in and out as you do).

 

Thanks guys! Going to look into this tonight and report back tomorrow!

 

This would rule out the side stand switch, but not the side stand relay. You can pull the side stand relay as a troubleshooting aid. When pulled, the TCI cannot be disabled by the side stand safety circuit. Cleaning the side stand switch should still be done as a periodic maintenance to keep it functioning properly.

Note: Only applicable if it has a side stand safety circuit - not present in the 81 model.

Or the entire ignition circuit including the fuse box and connectors as suggested. Has the fuse box been repaired/updated?

Neutral light is powered by the signal circuit, so not a good indicator of power present in the ignition circuit. However, the starter will not engage if power is missing in the ignition circuit. Have you had an instance where the starter would not engage when trying to start it?

 

Thanks Rooster, lol I was just searching all over the place trying to find the stand switch (1981). Someone did a total hack job on the wiring on this thing. There's not even a fuse box, just a bunch of inline fuses (all seem to be good) spliced in there hanging in the airbox area, arrrrgh. I have a feeling I'm going to be know everything about the wiring on these bikes by the time I figure this out. There was a problem with the starter earlier but it was just from all the crud where the brushes make contact (see pics). Haven't had a problem with the starter since I cleaned it. When it's light out tomorrow I'm going to take the headlight out and see what kind of rat nest is in there. Thinking I may end up redoing all the connections myself.
Starter pics:
https://www.dropbox.com/s/0mu9yl7nhhqskg3/IMG_0935.JPG?dl=0
https://www.dropbox.com/s/6eq60z3wphj1kpd/IMG_0936.JPG?dl=0

Also thanks MN-Maxims, good idea to put a plug in my pocket.
Cheers

 

XJ4ever has nice fuse box kits with wire pig tails so you can clean up the inline fuse mess. More importantly on a bike like ours, it makes great sense to go over every single electrical connector. I like to clean up the good ones and treat them with dielectric tune up grease. Keeps the moisture out and protects the brass from turning black and green. The three wire connector from the generator is very important to maintain since the plug will melt due to dirty high resistance connectors.
Side stand relay and the connector is a very likely problem area to look over very closely. Let us know what you find.

 

AH HA! (I hope, lol) This relay (main shutoff?) was laying on top of the engine due to the rubber mount failing. I'm thinking maybe it would click out from rattling around and kill the bike, forcing me to stop and put it in neutral to get it fired up again.
https://www.dropbox.com/s/ajtgyovee2lo0dv/IMG_1015.JPG?dl=0
It's now back in it's home with some electriacl tape after cleaning the contacts.
https://www.dropbox.com/s/nsyawd29syer03y/IMG_1016.JPG?dl=0
Hopefully this fixes the problem
Was good to pull out the headlight and see the mess in there:
https://www.dropbox.com/s/g0e12sni9gkvwkj/IMG_1009.JPG?dl=0
Not sure what the missing connections are for but there's no clutch switch that's for sure. Gonna her back together and take it for a test rip tomorrow. Fingers crossed!

 

ARRRGGGH. Darn thing quit again almost in the exact same spot as last time and then ran perfect for the rest of the ride. #confused! I still haven't cleaned the gas cap, will do that just to check it off the list.

 

See if you can swap with a known good TCI and go for a ride.

 

Hmmm interesting idea. Unfortunately I live in a small town and no one I know of has the same bike. That's a good idea though, maybe I'll open it up and see if I can see anything physically wrong/loose. I've replaced capacitors and such on computer motherboards so it wouldn't be out of the realm of possibilities to fix something but only if I could see the problem visually...

 

Might try the wiggle and tap test first. With the bike running, gently wiggle the connectors at the TCI, tap the case of the TCI lightly with a plastic handle screwdriver.

You can only inspect the solder joints by removing the cover, although there could be an issue. Otherwise, you must desolder the connectors to remove the CCA to inspect the components.

Might try gently massaging these areas a bit also with the bike running, particularly if they are crimped.

 

Tap/wiggle one thing at a time though. If you do it all at once and the bike runs you won't know which tap/wiggle solved the issue.

 

Uh-oh--- don't let MattiThundrr read that......

 

Jeez. I would protest, but Dave is right. I was thinking it.