Another weird electrical issue -- advice please

I bought this 1980 XJ 650 Maxim for $80. I was going to use it as a parts bike for my '83 midnight but it was pretty complete and sounded like a good project. According to the license plate, it hadn't be registered since 2005 so I guess it may not have been started since then. Odometer reads 10,000.

I checked compression first thing and got around 130 PSI in each cylinder. Next I just wanted to see if it would fire at all. Put in a set of new plugs and some starter fluid in the carbs. Nothing but a random buzzing noise after I turned it over for a while.

Took out the number 4 plug and looked for a spark while it cranked (grounded the bottom of the plug) -- nada. Then the buzzing noise started again (after I stopped cranking) and the spark plug I was holding started arcing from the bottom of the plug to the cylinder head (I was about .5 inch away from it with the spark plug). As soon as the buzzing stopped, the arcing stopped. Weird huh?

Not having enough common sense to stop there, I noted that there are two coils for the machine, one for the two inside cylinders and one for the two outside.

I pulled the plug out of the number two cylinder (putting number 4 back) and checked for spark. It sparked properly although I expected a stronger looking spark.

Does anyone have any ideas? Do I just have a bad coil? Have I fried my CDI? Should I give up on the bike and just use it for parts?


Thanks in advance!

 

It could be ANYTHING from the fusebox to a bad connector somewhere to a slightly soggy battery or anything in between.

All of the above are prime suspects; start checking/cleaning connectors at the battery and work upstream. After you check out the fusebox.

 

dont junck it get you a repair manul for it. best 20 dollors i ever spent. saves alot of time and headachs. im rebuilding a 750 thats been in a field for 16 years. its been a big help

 

Every time I've had a plug that didn't fire then got a spark when I moved the ground away from the engine was a fouled plug.

Try a different (known good) plug on that #4 wire.

Got no idea about buzzing. Hard enough with that when you can hear it yourself.

 

thank you for the reponses. These were brand new spark plugs. Here are a couple of other things I tried yesterday after reading the responses.

I looked at the fuse box and it seemed fine -- all fuses were good, blinkers work, neutral light works, tail light works.

I measured the resistance of the primary and secondary (spark plug wires) windings of each coil. Yamaha says that the primary windings should be 2.5 Ohms +/- 10%. One coil was 2.7, the other was 3.5 Ohms. The secondaries are supposed to be 11K Ohms +/- 20% . Both coils were good. They said that a spark gap test should be performed on the coils to really test them -- I have no idea how to do that.

Next I disconnected the 1,4 coil (that was in the circuit that was doing the weird sparking from the plug ground to the cylinder). When I cranked -- no buzzing.

Today I'm going to try to use the 2,3 coil in the 1,4 circuit and see if the spark works correctly. If it does not, maybe it means I have a bad TCI? -- yikes!

 

Do not fret Mariana, you have not yet tested the coils. You mention you have consistent firing off of one of the coils. Test both sets with that input, easy. Then test the known good coil on the non-firing plug to ensure it is good or bad.
The buzzing could be the starter coil (don't know for sure, gotta hear it to narrow it down). Could be the starter too. I get a weird "honk" out of mine if it is cold enough and/or I haven't started it in a while.
The TCI is an easy check. If you are getting spark out of one coil set, check for voltage at the primary windings of the suspect coil. If you have voltage as you spin the engine, it's not the TCI. If not, you need to ensure that the pickup coil for that coil unit is intact and working (another branch to chase but they are all connected). You should see about 650 ohms, give or take 50 or so ohms either way, on the pickup coils. If not, you have your problem cornered.
Good luck!

 

Ok my friends, here is the update on my $80 bike. By process of elimination I pretty much surmised that my issue was the TCI -- one of the channels was providing a ground even after I stopped pushing the starter button. That was causing the buzzing sound in the 1,4 coil because it was causing a continuous arc for 2-3 seconds.

I got another TCI from rpilot (thank you very much) and after cleaning and bench syncing the carbs, pulling off the oil pan and cleaning it, changing the oil and filter, repairing my carb boots, fixing the hole in the muffler with roof flashing...... it started!

Here's my issue now. It seems to be making a tweeting sound in time with the rpm. It also sounds like it backfires into the carb #1?

I have not done anything with the valves as I was a bit nervous to open up that can of worms and I don't have any shims or the special tool. Do you think that is the problem? or is there some strobe timing that needs to be done?

Thanks for all the great help. I would never be brave enough to do all of this without the support of this forum and it's knowledgeable members.

Chacal also sent me a couple of items and his usual great advice.

 

Your tweeting could very well be a tight valve, as could the backfiring.

Valve adjustment isn't that bad of a can of worms, but it IS a very necessary maintenance procedure and something you shouldn't put off.

The special tool costs less than $20 and is widely available; and you don't need any shims until you've checked the clearances and "read" the existing shims.

Read this through, it applies to your bike too: http://xjbikes.com/Forums/viewtopic/t=14827.html

 

I agree you should check the valve adjustments. The intake on # one is tight it could be your backfire although with those compression numbers it sounds unlikely. The tweeting noise,,,,,without hearing it it is hard to say. I will say that my 650 and almost every one I've been around does have an RPM related noise with them. Sounds kind of like the noise a supercharger belt makes on a V8. I've been told it is due to the straight cut gears coming off the crankshaft. If its backfiring it may be lean on that cylinder. Check for induction system leaks (air), around the boots on both sides of the carbs. You may be able to smooth it out by coming out on the idle adjustment screw. Good luck and enjoy your $80 runner!

 

If it's "Tweeting" and backfiring ... I'd look for an Air Leak letting fresh air get into hot exhaust gases.

If the Backfire is more like a Bad Cough, ... it could be Exhaust Gases re-igniting.

Rap on the Head Pipes and see if any of them "Ring" like a bell, instead of just "Danck" like a tight pipe being mufflled.

 

Great! Thanks guys. I'll check those things out tomorrow. I looked on BikeBandit and a new gasket for the valve cover is $34. Is that what you are all paying every time you check the valve clearances? I guess maybe with the silicon grease specified in BigFitz's write up maybe you're good for a couple of adjustments. Maybe Chacal has a better deal.

 

If that's NOT a YICS motor, and I'm pretty sure it's not, then yes, chacal has a better deal (by far.)

If you glue one side of the gasket to the cover and then use silicone grease, (or motor oil, MMO, axle grease, whatever suits your fancy) on the other side, you can probably re-use the gasket next time. Remember, it's a 5000-mile service, so depending on your riding habits, it could be a while.

You might want to replace the rubber half-moons this time if the cover hasn't been off in a while.

 

Thanks bigfitz, definitely not a YICS. I'll check with chacal for the gasket and the tool.

 

I'd be interested in your old TCI Marianadeeps. I'll PM you with questions.

 

Shoot. after I installed the other, I took it apart and had a tough time doing it. I'm afraid it's in pieces now (circuit board broke. If you wanted to salvage some of the components i.e. the transistors or the IC those might be usable. I was going to test the transistors to see if one of them was blown, maybe I could replace it. There are some other discreet components e.g. resistors and caps. Sorry, couldn't help myself -- I'm an EE.