Low spark on XJ650

Hello everyone
I have extremely low spark and the engine will barely stay running, maybe 5 seconds at at time If it starts, the compression is great accross the 4 and almost equal 120-125 psi. Pickups look very clean, new battery.

I'm saying the spak is low looking at the arc from inside the plug boot to a screwdriver tip.
I know there must be a better way to check spark strength but I don't know how and hope it's cheap.

I don't know if this is related but here goes, the fuse cluster isn't screwed down so if I turn it away from the left side of the bike the starter won't turn, when I turn it another way, the start turns. I bought a new fuse cluster and wire leads frm Chacal but it's going to take some time to replace it all and I'm a little injured at the moment.

I don't think it's related to the bad spark but please let me know otherwise.

Any Ideas anyone?

 

Spark is pretty weak from these coils regardless. If you have consistent spark, it's probably not your problem.

If you want to see the spark, you can get some little inline spark "windows" from Harbor Freight for about $5.

I'd recommend you pull off your intake boots, open the throttle up, and spray a bit of instant start in each carb... then start 'er up and see if she runs a bit longer. I suspect that you have a fuel/carburetor problem, and this test would help confirm that. Should rev up well and run 5 - 10 seconds off the instant start.

 

Any thing draining power or reduce flow will reduce your spark on these bikes. (A low battery will turn it over but not let enough spark be thrown to start her up). So, go ahead and fix the wires since you already have the materials. If it doesn't fix the issue, you will have eliminated one possible source and you were going to do it any way.

However, I agree with SQL that its probably not the spark if it runs for a short time then dies...

 

I had this same problem. Turned out, the inline fuse holders that the PO had installed were separating from the wires coming out of them. Looked like the wire had gotten brittle over time. Replaced the fuse holders with new ones from autozone and haven't had any problems with it since.

 

I would install that fuse holder when you feel better and then check your voltage at the battery when bike is running to see if your charging properly. Your brushes in the alternator my be worn out.

MN

 

Thanks a million guys. I can't say enough about this site. I almost had the opportunity to help my first person about coils yesterday but by the time I got to forums page 4 it was solved - can't wait to return the favor

Anyway, I'll post the update later today. Thanks again

 

OK changed the fuse panel and problem remains. Checked alternator brushes and they are 12mm each. Going to get the starting fluid soon today. I'll keep reading...
Thanks Again

 

Time to get a multimeter and start checking continuity...

 

alright ya'll, starting fluid started it. I yanked the carbs, (i thought I rebuilt them Perfectly from the printed pages from our wonderful forum here. I took two weeks doing it and considered it my bible for those two weeks.) I guess I was wrong because when I took the float drain screws out a different amount of gas came out of each bowl. Then I put the gas tank on the edge of the bench, connected the gas tubing to the carbs and turned the petcock to Prime with the bowls off to check the flow. It seems like they're all flowing well so I guess it's the float levels. But I must admit, after all that reading, I still wasn't sure of the float levels. So I guess I have to go back to that forum and redo the levels and Try to understand the references again.
- your input is greatly appreciated and valued -
Thanks

 

Use the clear tube method, it's the only way to be sure of the level in the bowl & yes it is a PITA.

 

ok so fuel supply above, 4 clear tubes to the bowl drain holes, prop the 4 tubes up higher than mid carb section, loosen all 4 drain scews, and do a visual check of the fuel level, adjust as needed?

 

I just do them 1 at a time, as the levels are not relative to each other, just relative to the gasket line on the bowl (2mm below)

 

ah that's interesting. so the gasket surface is recessed a little, so should I compensate for the space I can't see, or measure 2mm down from where screw heads touch?

 

The top blue line is the gasket & the lower blue line is where the fuel in the tube should line up with i.e. 2mm below.

 

I didn't have the guts to start a new topic for this next question; :roll: shoud I see the cylinder valve moving inside the carb body when I open the throttle? Cause I'm not. 8O

 

Only if the engine is running, they work on vacuum.

 

Thank You Wizard, I thought it was so funny to see noone answered

I am proud to say this problem is almost closed out after 18 hours in the garage this weekend. It was a combination of all 4 float levels being too high and different and low spark on #'s 1 & 4.

So I learned that the revs won't come down until the intake is completely buttoned up, airbooot clamps, air filter, air box lid and ALL THE INTAKE VACUME PORT CAPS ON. I was running the bike with the gas tank on a shelf using a long tube while set to the Prime (turning it to On everytime I shout the bike off, but I must admit, after the carb rebuild and correct setting of float leves, the carbs don't overflow while on Prime.)

learned how to cehck compression, alternator brushes, pickup coils, and test coils.

turns out there is too much resistance on a coil bumping the Ohms to 27,950.

After I finally got the bike road worthy I knew it should have had more balls so I started checking the ignition following the Haynes manual and Chacal's notes.

So she's finally puring like a kitten and the new Dyna coils, wires and caps are on they're way from Chacal.

I added an attachemnt pic but it doesn't display anything...

Thanks to All

 

Congrats man...

 

Very cool - amazing what you can learn off this site. Been a very valuable resource for me.

 

Was this measured with the plug caps on or off? The plug caps are 5K Ohms each, but the manual forgets to mention that. The resistance measurements in the manual are for the coil only, without caps. The caps screw in to the cables.

Please let us know what kind of a difference you notice with the new coils.

Cheers,
Paul

 

The brass slides move when the motor runs as the throttle plate opens.

When you PULL the cable, the butterfly opens and the airflow increases through the venturi. (space below the slide) As the RPMs increase, it causes increased suction, which flows through the holes in the slide, creating a low pressure area in the HAT, ABOVE the diaphragm. This causes the diaphragm to pull the slide UP, in turn pulling up the main needle and allowing more fuel to flow for the higher throttle plate opening, thus balancing the air/fuel ratio.

Keep in mind, the term vacuum is used loosely. A vacuum is not possible. It's really just a suction and low pressure zone, moving to a high pressure zone. Vacuum has just been used to describe this movement of low to high etc.

 

Actually...

"vac⋅u⋅um /ˈvækyum, -yuəm, -yəm/ Show Spelled Pronunciation [vak-yoom, -yoo-uhm, -yuhm] Show IPA noun, plural vac⋅u⋅ums for 1, 2, 4–6, vac⋅u⋅a /ˈvækyuə/ Show Spelled Pronunciation [vak-yoo-uh] Show IPA for 1, 2, 4, 6; adjective; verb
–noun 1. a space entirely devoid of matter.
2. an enclosed space from which matter, esp. air, has been partially removed so that the matter or gas remaining in the space exerts less pressure than the atmosphere (opposed to plenum ). "

A total vacuum is impossible, but a partial vacuum is totally possible.