Can't get my XJ to run

[BillyRok]

It's been almost two years since I've put any real time in riding my XJ. My last trip I had troubles restarting the bike after gas stops, it wanted to backfire on occasion, hard enough once that the rubber plug on #3 carb port blew out going down the road.

Since it sat for a while, I pulled the carbs off to clean. Ran them through my ultrasonic with Branson cleaning solution. All internals are stock Mikuni, butterfly shaft seals and idle mixture o-rings are new, float levels are good, carbs were bench synched and leak tested.

Put the carbs back on the bike and it won't fire. Pulled the plugs after cranking the bike with the enrichment circuit on but they are dry as a bone. One at a time I also pulled each plug and grounded it against the head, a quick hit of the starter revealed spark on each one. I even put a bit of gas in a couple cylinders before cranking it but still not even a pop.

So I started dong some research into possible electrical issues and came across this so I did some quick checking on voltage.

The power goes from the ignition switch through the ignition fuse, then the emergency kill switch to the ignition module and the coils on the red/white wires.

The battery is 3 years old and has been on a trickle charger off and on. Had 13.4 when I unhooked the charger but seemed to hold around 12.6 while testing as the headlight comes on with the key on with the XJ. With the key on I had 11.1 at the ignition switch, 10.6 at the ignition fuse, and 10.45 on the R/W wire that feeds 2/3 coil and 10.2 on the R/W wire that feeds 1/4 coil. Both coil readings on my multimeter start out around 8.25 but jump up to the readings over 10 after a couple seconds.

I then left the bike sit for a half hour or so, then decided to check voltage at the main fuse which I think is at the beginning of the ignition circuit. At this point the battery read 12.85 and I got the same thing at the main fuse.

Couple other points...the valves are in spec and I've ran another ground wire from the regulator rectifier to where the battery grounds to the frame.

Any thoughts, ideas, or guidance on helping me sort this out would be much appreciated.

[skids]

I also have had issues with restarting after stopping for lunch. Not so much for a shorter stops like refueling. I know this will not make much sense, but mine started by pulling the choke all the way out and open the throttle a bit (seems counter productive as this is not how you start a cold engine). I don’t know why it wasn’t just starting up after lunch breaks but I suspect that the carbs got so much radiant heat that they were overly lean.

Concerning blowing off the nipple plugs, I think there is some back-fire pressure happening. Too lean? Bad exhaust system?

[soccer4m]

xj

HOwdy BIlly,,,, I have an xj also,,,,if you have the octopus on the bike, get rid of it, it causes numerous problems and just connect the carbs with fuel line, also put in a fuel filter in each line.

Since you have spark, the ignition circuit sounds good, try spraying some instant start in the air cleaner opening, seat off, and put the petcock on prime.

Also, you can try to squirt some gas in a spark plug hole and put plug back in, spray instant start, petcock on prime, and crank it. If it fires your octopus is probably not allowing the gas to flow. easy fix. if it fires and runs you can also run the bike on prime just remember to turn it back to run when done.....keep us informed....mike in sun diego

[DiverRay]

+1 on what Mike said.
Also, you should clean the connections and contacts on the bike. Your voltage drop through the ignition switch/kill switch is a little too much. If you drop below 10.5 the ignition will not work. You are at the limit now, so maybe start with the ignition switch. Two 10mm bolts and one plug to remove, three screws IIRC to take it apart, clean contacts and re-assemble.
If you still have the glass fuses, you NEED to replace them with the newer style blade type. There should only bee about 0.1V drop through a fuse. Also, clean all the ground wires and put anti-seize on them. that will help the electrons flow.

[Radioguylogs]

Other members have mentioned things that would match the dry plug symptom.

In case it helps:

(1) I recently had a bad battery on my SF. It would do that same thing where the voltage would be low, then suddenly jump higher. It failed right after I started the bike one day. It died immediately after it started and wouldn't even fire until I replaced the battery.

(2) I don't think you were were working on the coils before you had the problem, but I had the 12V coil wires backward on the SG Bagger when I first got her together. The symptoms were it would fire, but not start- so the symptoms don't match your problem, but JAT.

Good luck - We know you'll figure it out.

[BillyRok]

Some further details...

I have the synch gauges hooked up to the bike and am running a temporary fuel supply to the carbs so the octy is bypassed right now, and I do have inline fuel filters. Did try some gas right in the cylinders, it's worked for me in the past but not this time. I guess I could give it a sniff of ether to see if that does the trick. Old glass fuses were replaced several years ago with the one TC supplies. I got the 10.6v reading at the ignition fuse on both sides of the fuse so I have no voltage drop there.

I'm puzzled why the plugs would not appear wet after cranking the motor over for several seconds with the enrichment circuit fully open. And if I have spark at each spark plug when grounding them to the head, doesn't that mean I have voltage enough to fire the coils?

I'm pretty sure the grounds are shined up but will check again. I've had the ignition switch apart before. Looked good but I still took some fine sand paper to the copper contacts as long as I had it apart. It must be possible to check resistance through both the ignition switch and kill switch with a multimeter, I'll see if I can figure out how.

[motoman]

Battery showed charged after being re-charged, which is just a 'surface charge' at that point. Once a load is applied to battery from starter, its voltage fails way lower than you would think. Have seen this happen many a time in the automotive world. I suggest replacing that battery as bike has basicly been setting dormat for some time and one or more cells has started the sulfation process. Purchase a NEW quality brand battery, initially charging it using a 1amp charger before installation. Install it, and enjoy riding that XJ once again.

[motoman]

In reference to my previous post, attach volt meter to battery and engage the starter. This will show ACTUAL battery voltage when under load. When bike is running at idle, this test will also show voltage regulator out-put, which should be in the 14.5-14.8volt range.

[Eastcoaster]

I gotta ask

I have this bike when you cleaned the carbs are you sure the port holes are open in the carb bowels to allow the enrichment to work. I had a heck of a time getting them opened once I did it fired on a tap. Bring the bike to jersey I will get it going

[BillyRok]

Yes the ports in the carb bowls are clean, spraying carb cleaner through the little red straw into them sends spray squirting across the room.

Is it possible to have spark when grounding the plug against the head but not have it when the plug is screwed back into the combustion chamber?

[skids]

Is it possible to have spark when grounding the plug against the head but not have it when the plug is screwed back into the combustion chamber?

I would think that the grounding is comparatively better with the plug installed.

[skids]

If you can’t get it to start hot or cold and you have spark, it is either fuel supply or compression. If fuel flows on prime settings, the filters are not plugged. Compression is easy-enough to check.

[Radioguylogs]

Is it possible to have spark when grounding the plug against the head but not have it when the plug is screwed back into the combustion chamber?

Theoretically, yes:

https://www.agriculture.com/machiner...gnition-system

Don't know how probable it is in practical situations.

[BillyRok]

Thanks for all the replies. I got thinking about what Motoman said...

Once a load is applied to battery from starter, its voltage fails way lower than you would think.

So I went out and checked the battery again and got 12.83v with the key off. That drops to 11.3v with the starter turning the motor over.

Then I checked the R/W wires at both coils with the key on and both were at about 10.5v -- However with the starter engaged, the readings dropped all the way down to 7.5v, I didn't expect to see such a big difference.

I guess tomorrow I will jump the bike off of my pickup and see if it fires but it looks like what I thought was a good battery is not so much.

[motoman]

At this point Billy, with replacing the battery, I suggest you also remove the stop/run switch, take it apart(careful of the teeny spring inside), and place switch assembly including switch itself in a shot-glass full of Evapo-Rust. Leave it in for a few hours, then remove and wash all pieces with water and blow dry with an air hose. Re-assemble and re-install switch. Those particular internal contacts COMPLETE the running circuit, and when those contacts are cruddy, voltage is lost and also attributes to voltage regulator constantly charging battery at a higher rate than necessary, which in turn reduces life of battery. Hopes this all is of help with maintaining the constant running of the XJ in the future.