Weak Spark

Hello All,

I purchased an 81 XJ 650 in the fall last year, and have begun getting her road ready for the spring. I found this website and could not resist joining. I really like the bike, and can't wait to get a lot of miles on it this year. I've had a lot of experience with auto repair, but am new to motorcycles.

I bought this bike last september, and it had a funky ignition problem, which is why the previous owner had let it sit for a few years. It will run fine upon start-up, but once the engine is under load, it starts breaking up (@ cruising speed, it is fine). Also, in wet or cold weather, the spark in cylinders 1 and 4 pretty much disappears, and the bike won't start. For reference, my plug wires are horribly dry rotten, and the coils don't look to be in the best of shape.

Sounds like a pretty open and shut case of bad coils and wires. I've got great compression in all 4 cylinders, and I've cleaned the carbs. I know there is a lot of power in that motor, but the spark is keeping me from getting at it.

Has anyone else had this problem, or a similiar one? Did swapping out the coils make a huge difference?

I've got a used set of coils off ebay en route. I'll have them installed the next day I get decent weather in Cleveland.


Thanks!

 

http://www.geocities.com/MotorCity/Spee ... g.html#ign

Welcome dfijalk 1;
Check out this link, it might give you some things to look for.
I was born and raised in Canton, most of my family is still there.

 

Thanks for that link, I'll use that for a reference.

I'll post an update after I get the coils installed.

 

You need to measure the resistance of the coils AND your resistor boots to make sure they are within specs. Also, make sure the plugs are non-resistor type. Have you replaced the plugs with new ones? Have you cleaned the contacts to the coils? Another spot that corrodes is the wires themselves. The resistor boots and the coils have threaded points that the the wires screw onto. Take the resistor boots off first to see if there is corrosion present. Getting the wires out of the coils is another issue. They are epoxied in, but there are instructions for removing them and putting in new 7mm copper core wire.

 

I have brand new plugs that haven't been installed yet.

The wires are in terrible shape, and there is green corrosion growing on at least 2 of the boots. Everything is basically dry rotten and in pretty sorry shape. When the bike does get going, the wires do arc.

I haven't cleaned the contacts to the coils, I will do that when I replace the coils with the new used set I got off ebay. when I do the coils, I'll clean up everything under the tank, and do it the right way say I shouldn't have to do the job again for at least a few years.

I didn't know there was a way to put new 7 mm wires on those coils. That is interesting. Maybe I'll try that on the set of coils in the bike. It never hurts to have some spare parts around.

I strongly suspect the coils and/or the wires are the culprit, do to the arcing, and the sensitivity to wetness.

 

The instructions for replacing the wires is on the XJCD.

If your wires are arcing, then there is your problem. The XJ needs all the spark it can get.

 

I've got my fingers crossed, hoping that the new set of coils fix the problem. It really should fix the problem. If it doesn't, then at least I've eliminated coils/wires as an option.

singinotter, where at in NW ohio are you from?

 

Yup - that sounds like the classic symptoms of bad coils that the XJ's are sadly famous for.

You already mentioned the wires were in bad shape - I betcha if you check the coils you might find yourself some small cracks - that's what happens.

OEM replacements are fine, but what you really want are either the Accel or Dyna replacement coils. Both require some creativity (and/or modifications) to get them mounted, but are well worth it. Both offer MUCH stronger spark, and give you the option of replaceable wires. Note - you want the 3 ohm, dual output coils.

 

I replaced the stock coils on my two Maxim Xs with dynas, new leads and iridium plugs. Big improvement, they start first time every time, tick over like a watch and are not affected by rain. The job takes under two hours and is not difficult at all. Approximate cost coils/leads (excluding the spark plugs) 150USDollars.

My old coils had hairline cracks which give trouble when the coils heat up or get damp - Dynas are a permanent solution.

 

can u show us how u mounted the dynas?

or at least tell us how u did it!

would they fit in the same place as the others?

 

Greetings and welcome to the wonderful world of the XJ's dfijalk1. You'll be plesantly surprised at how docile the 81 XJ is. It's handling makes it a perfect first bike. I have had the coil issues myself with both of my 81's and the Accels were my fix. I'll try to shoot pics for everyone sometime soon. The factory coils are nice but are expensive. The old coils can be saved if, and only if, they ohm out correctly for the primary windings. If they do, proceed to cut out the secondary wire from the housing using a dremel and a gentle hand. Once the wires are escavated, cut the old wires off and splice and solder a new set of 7 mm wires into place. Re-pot the wires with epoxy of your choice (POR makes some awsome marine epoxies) and terminate your wires with new boots. Viola, your spares are golden!! Had the coil sets on both my bikes puke and cause misery in my life. But they are great rides. Good luck!!

 

Good news.

My coils arrived today, and I promptly installed them in my bike. To my delight, I'm getting nice crisp snaps of blue spark at the plugs when I turned over the motor.

Unfortunately, I think I have a little fuel line freeze up here in ohio, it's about 20 degrees. Starting fluid would let the motor run for maybe 5-6 seconds, then it would die, it wasn't getting any gas. Oh well. I'll try starting it again when it gets a little warmer.

Thanks for the advice!

 

hope it works for you mate , ive got a '81 650 aswell :wink:
cheers brenton