Xj650 no start and backfire

I have a 1981 Yamaha xj650. I've replaced the motor about 2 months ago and have been riding it ever since no problems.

In the morning coming from work I stopped at the gas station to fill up. Before I went to switch off the key the bike shut off. Didn't think much but when I went to crank it many times, it wouldn't start.. I waited for a tow about 15 mins decided to try it one more time and bam starts right up without a problem.

Later that day I was on the freeway, again no symptoms of it having any problem. Happen again while I was going 80mph. I thought maybe I moved the engine stop switch. I cycle the switch while I was still moving and gave it throttle and made a very loud backfire like a sound of a gunshot. Got the bike towed home.

I've looked to see if there was fuel flow from the peacock. Yes
I replaced the Sparks plugs and yet no start just cranking
I have a box to test if there is spark going through the wire( like a probe clamp) and yes. Unless there is a better way of verifying.
I disconnected and connected the connectors of the cdi and no start.
Verified the firing order

Bike cranks over no problem.. tried spraying carb cleaner and/or starting fluid and nothing.. sometimes even does the gunshot sounding backfire

Any ideas would be greatly appreciated.

 

Begin by verifying all electrical connections are cleaned and tight

 

Take your time while chasing the electrical gremlin. As Stumplifter said, check and clean all the electrical connections. Even use dielectric grease to help with the connection. As you are pulling the connections apart you might see a little puff of powder from the corrosion, this is normal for the older bikes. You might even fine a wire or two that has been pinched or rubbed to the point it becomes a problem.

Good luck and keep us posted.

 

Particularly the fuse box if it has not been upgraded. The fuse clips degrade over time and cause intermittent connections, and sometime even break causing no connection.

Here is a link to the how-to:

http://www.xjbikes.com/forums/threads/how-to-install-an-aftermarket-fuse-box.6350/

 

This, fuse box gave me the exact same issues as your bike until I replaced fuse box with all in line fuses. If I had to do it again, I would have bought a new fuse box with blade fuses, would have looked better under the seat.

 

LOL That part's normal. You loaded the exhaust system with raw fuel, it vaporized, and when you popped the ignition back on the hot exhaust gasses made it all go BOOM!
We used to do that for fun whan I was a teenager.

I do not think that this is an electrical problem, because...

So: Hard to start when hot. Restarts when cooled down. Stalls again once hot.
When was the last time you checked the valve clearnaces?

Still not starting when bone cold.
Do you have an inline fuel filter installed?
If so, what type (paper or metal filter media)?

Have you pulled the plugs and checked for wetness (cylinders are getting fuel) or dryness (cylinders are not getting fuel)?

If you want to double-check that there is spark, pull one plug at a time, lay it against the head where you can see it, and hit the starter. You will see the spark if it's there (it's easier to see it in the shade). Replace the plug, and repeat the process with the others.

 

Sorry for the late reply havent been home to work on the buy. Lots of hours at work. Anywho I appreciate everyone giving advice and help. So today I decided to check arc from the wire connected to a plug and holding it next to the cylinder head. I get spark from cylinder 1-4 but no spark on 2-3. I had an extra coil, swapped them and still no spark.. I'm still going through all the connectors and grounds to verify everything is good.

My left control switch has been a bit faulty lately, there has to be a sweet spot in order for the engine to start cranking, anything to do with that?

Relay "4H7-01" does click when I hit that sweet spot on the control switch. Although I noticed with a test probe that the 2-3 ignition coil doesn't get as much power as the 1-4 coil does when I switch the switch to "run".

All my fuses box upgraded and are good.

Thanks again for ur help

 

left control? high low beam horn choke.
remove the (righ t)control with run switch and starter button and clean contacts and lube, Just did this today run switch sends voltage to tci and coils, also feed the "4H7-01" which feeds the solinoid .

you did say starter working just no spark on 1 coil pack

have you ohmed out the pickup coils? this is done at the tci connector

The Ultimate Relay, Switch, Sensor, and Diodes Guide

Pick-up coils:
1980-81 XJ650 Maxim and Midnight Maxim: 700 ohms +/- 20% = 560 ohms to 840 ohms acceptable range


"4H7-01" is the starter cutoff relay

 

Have you found a fix yet?

 

Thread revival - 5 yrs and a bit...