1980 xj650 Maxim engine problem

Good evening all.
I would love to pick some of the experts minds on this site if I can, I have a problem that is getting worse. I have read a heck of a lot on this site but I don't want to adjust anything unless I have too. Not a bike mechanic here, just a novice wanting to learn more.

I have a 1980 xj650 Maxim with about 50,000km on it.

The bike had a tendency to shut off in mid ride. No back fire, no chugging, no lurching, no warning at all. This would happen once, we would wait 5 mins, and it would start perfect and run great the rest of the ride. And then the next ride it wouldn't happen, this would continue on and off. This was last year.

This year, same problem. BUT I had a stuck float, so I took the carbs off, cleaned the inside of them and put them back on. I did not adjust any screws at all, except for the idle screws(the three very clear ones facing the front of the bike) to have the bike idling at a good RPM's of 1000-1200. I also replaced the air filter, the 4 hose's going into the carbs from the air box and also the outside carbs hose's going into the engine.

Something extra now is happening, it is now backfireing and then stalling. Before it would happen once/twice per ride. Now it is happening double that and for longer periods that you have to wait. Any questions/suggestions would be most helpful before I dive in over my head and really destroy something. haha If you need pictures I can pictures.

 

I'm no expert, but I wonder if you accidentally adjusted the sync screws instead of the idle screws.

There are three sync screws, which are large, slotted-head and exposed screws. The idle screws are also accessible from the same area, but are contained in a (usually) open ended cylinder about 1/2 inch down, and are much smaller, slotted-head screws.

It sounds like you adjusted the sync screws, which means you'll be best off pulling the carbs (get used to it! ) and doing a bench sync to get them back to a rough-spec. Search "bench sync" here and you'll see it's very easy to do.

Good luck!

 

Do you have spark after it dies? If not, could be a bad solder joint on the TCI module...just a guess without further info.

 

I agree with shnuffy. You have 3 synch screws, 4 idle mixture screws and one idle adjustment knob.

 

Oh......do i ever feel like a tool now. :lol: haha...well I guess I must get used to it. Thanks for the help. I did adjsut the sync screws thinking that they were the idle ones. My god, I feel like a tool now. but I will look up how to bench synch and take it from there. Thanks Shnuffy.

Ski84 - ya it does have spark after it dies. It wants to turn over but doesn't for a little while and then starts no problem.

So after I bench synch the carbs will that stop the bike from shutting off mid ride? I think the bike might be running too rich because it was doing that before I touched the carbs. So would it be smart to adjust the mixture screws? Or is there something else I should check before I mess with those?

Thanks for the help.

 

Hopefully one of the experts can confirm or deny the following advice:

1. Not sure about your bike shutting off.

2. The bench sync should drastically help any roughness in the motor. It's easy easy easy to do.

3. Screw all of the idle screws all the way down (using a screwdriver that fits them exactly!). Then, unscrew them 2.5 - 2.75 turns out.

(2) and (3) should set your bike up well enough for a fine-tuning afterward (true carb syncing, colortune idle, etc).

Again, I don't know about the bike shutting off. Could be electrical. I'm not totally sure of the overall condition of the bike but it sounds ok. Hopefully these few things will help out enough.

For a truly beautiful ride, check out RickCoMatic's carb cleaning thread. It's an exhaustive description on how to get the best out of your sensitive carbs and bring them back to new.

Chacal is the resident parts guy here and can get you anything and everything you need.

Good luck!

 

Hey, another XJ'er from S'toon, welcome!

From the description it sounds like you had sticky float problems last year. Likely they would get a little less sticky the more fuel that went through them, that's why it would get better as you ride.

Reminds me of a problem I had with a bike where it would die like that but the lights would also go out. It ended up being a bad connection in the fuse panel, new panel solved that. Another bike I had died in a similar way as well and that problem was a wire hanging too close to the exhaust and intermittently shorting out.

When you cleaned the float valves were they moving freely? Any resistance at all is a problem. How were the pilot jets when you had the carbs apart? Small gauge guitar strings work well for poking through to clear the hole. The emulsion tube has little holes in the side that also need to be clear to get enough fuel. How did the slide diaphragms look? Any pin holes and they are no good, also slides need to move freely, drop them in the carb and they should "clunk", hence the "clunk" test. Another thing to check is the petcock on the tank. Try setting the petcock to "prime", if it runs better, either the vacuum line is not sealing or the petcock needs to be rebuilt.

The backfiring could indicate a lean condition caused by a fuel blockage or vacuum leak as above or a vacuum leak between the carbs and the engine. It could also indicate weak or complete lack of spark on one or more cylinders. When it's backfiring, spray some water on the pipes, pull the plug on any cold cylinder(s) individually and check for spark on the wire by sticking a screw driver in the plug cap and hold it near the engine head. It should be both visible and audible. Or if you are touching the metal part of the screwdriver and the bike, you will also feel it.

It's possible as the others have mentioned that you inadvertently de-synced your carbs if you turned the wrong screws. That could cause your carbs to open at different times, not sure if that would cause your backfiring though.

Let us know what you find.

Cheers,

Trev

 

ok don't touch the mixture screws yet, the small flat heads in the recessed holes. you definitely need a bench sync and what you've done will definitely cause backfiring. I'm 99% sure your bike shutting off is a crappy connection, a 1980 stock fusebox should be the first thing you change, the originals are total crap, even if it looks ok. touch the wires coming out of the fuse box while it's running and see what happens. since you're just getting started my advice is Don't touch the mixture screws unless you buy a colortune plug. the idle screw is between 2 & 3 facing the rear of the bike, it's a knurl screw - doesn't accept a screwdriver. let us know

 

This is great guys. Thanks a lot. I do appreciate the help.

So first things first I will bench synch the carbs, I will not adjsut the mixture screws at all yet. I did clean the carbs before and they looked good with no problems. Floats were a little dirty, but cleaned them up. I don't think it needs to be done again.

I will then buy a new fuse box, anyone know how I can get a hold of that guy who sells the product on this site?

Once that is done I will update here on the performance of the bike, hopefully we get some good weather so I can actually test it.

 

GOOD. go to the home section of the forums and he's the first link at the top of the page Marketplace 'supporting vendor'