I'm getting too old for this--maybe

My XJ700n has been running perfectly for the last several months. But today it cut off for not apparent reason. It would crank over but not fire off. If I waited a few minute it would act like it was starting but wouldn't. It acted like it had no gas, but the tank was about 1/2 full. Finally I call the wife and she picked me up so that I could get the trailer to get it home. That took about 30 minutes. Sure enough it fired right up and ran for about 30-45 seconds and died. So, it appears to me that I have a sudden fuel problem. I'm interested in suggestions on trouble shooting this before removing the carbs. They are clean and I run a good inline fuel filter. Setting he petcock to prime did not solve the problem.

 

take the fuel line off, see if reserve works then

 

Fuel cap vent may have become plugged, resulting in a "fluid lock" in the tank..........pop the cap open next time this happens, see if you hear a "whoosh" and can then start it again. Also, make sure there no upward rise/ramp in the fuel line, a vapor bubble can form in such a spot.

 

I would have thought, given he said that there was half a tank of fuel in there, he would have allready done that? Isn't it the first thing everyone does?

 

Do you have an auxiliary tank you would use to supply fuel to balance the carburettors? Try that to see if it runs without cutting out.

 

My father told me that when I was young. He opened the fuel cap on my MZ and the bike started. It was no head turned that old two stroke but it got me to work and then I wanted another bike. Had a cup on the underside of the filler cap to measure the two stroke oil.

 

Is the filter on the Petcock There?
My 700 did the same to the PO. He was using a different tank without a filter and the carb fuel lines were plugged solid with rust.

 

Yep, first thing to check is that you can verify that fuel is flowing

 

Another thing to check is to replace the fuel line from petcock to carbs ...it is possible it can collapse inside line.

 

That would be part of verifying fuel is flowing

 

Thanks. The first thing I did was open the fuel cap and that didn't help. Tomorrow I will start the process, and I'm sure hoping it is somewhere in the fuel line or at most the petcock. I'll let you know.

 

Here’s what I find is the easiest way to determine fuel flow to the carbs......
1. Pull the fuel line off of the carb fuel “T”
2.turn the petcock to PRI.......fuel should freely flow. If it doesn’t, or just dribbles, open the cap. If it now flows, your cap valve is stuck. If it still doesn’t, you have to work your way back up up the line
3.if it Flows freely on PRI, switch to RUN or RES and turn the key on and press the starter button. The vacuum should open the petcock diaphragm and fuel should flow. If it does, the issue is in your carbs. If it doesn’t the issue is with the petcock, vacuum line, or tank

 

that could be a heat problem, looked at the valves lately?

 

Finally got around to trouble shooting the problem today. Here is what I have found.

Battery, 12.87 volts, 12.75 v at idle, 13.8 v at 3000 rpm
All plugs firing and look very good--nice light gray color
Disconnected petcock from fuel line--it pours gas at Prime and at both Run and Reserve (with engine running)
Fuel filter is clear and gas pours through it
No water in the fuel
Ran the carbs dry and set the petcock to Prime. All carbs filled and would flow gas from the nipple when the bowl screw was opened.
Checked the sync and the carbs are in sync
Valves were adjusted within the last 4000 miles and I have a nice ticking sound.
Right now the bike starts, idles and seems to run perfectly in the garage

The only thing I see that seems odd to me is that there is always air in the fuel line between the petcock and the filter but fuel can be seen passing through it. My filter is located midway between the fuel T on the carbs and the petcock and is not quite vertical. I have everything positioned so that there is a constant upward slope in the fuel line so I am somewhat curious as to why the bubble would not pass up and through the petcock, especially at Prime. (Interestingly, the same thing happens on my Honda Rebel, but it has never caused a problem, and I've been told that it is fairly common.)

Before this happened I was confident that I could take the bike anywhere anytime. That confidence has been shaken. Not excited about taking the carbs off . Could there be some electrical (I hate electrical) issue that would cause this?

 

when it quit, did it quit like key off or did it sputter out and die slowly?
would it start right now

 

That makes it sound more like the relay issue I had with my 900 a number of years back—-sudden quit, dead as a doornail.... trailered home—- found nothing, three days later while just standing next to the bike I heard a single faint relay click. I touched the start button and it fired right up.... never happened again

 

When it left me on the side of the road I was coasting to a stop sign and it cut off. Let the clutch out to try and jump start it but it would not. Coasted to a stop and it cranked over very well but sounded like it was getting no fuel. Got the trailer--about 30 minutes-- and it fired right up and ran for about 30 seconds and shut down and would not restart. A couple of days later I hit the starter and it fired right up. It shut down after about a minute, but it has often been a little fussy until it warms up and reaches normal idle --about 12-1300. Right now it starts easily and seems to run perfectly.

What relay would I be looking for and where. Electrical is not my strong suit.

 

I don’t know, cuz when mine did it, it was dead. Wouldn’t turn over. Wouldn’t do anything even with a jumper battery.......absolutely nothing, til a few days later and I hear that tiny click somewhere.

 

Be sure to check your coils and the TCI, they'll both break down with heat and then work again when they're cold.

 

I have ohm'ed out the coils but I will look at them again. Have no idea how to check the TCI, and in fact I'm not sure I even know where it is. Like I say, electrical is my strong suit.

 

TCI is the black box with the big plugs, near your regulator— the square aluminum finned thingy

 

I would pass over the coils - you lost both together, and they're very seperate. Not sure about the tci - how much electronics does each "side" share?
Fuse holders?
Maybe carry a screwdriver with you so you can verify carbs full if it happens again? But it doesn't sound like fuel to me.

 

Still sounds like fuse or relay

 

I looked though the wiring diagram this AM, if it is cranking I wouldn't suspect fuse as it wouldn't crank if that were faulty/bad connection. The sidestand relay could cause a crank/no start situation if faulty though. I read through the thread and I think you already confirmed that there is spark when it is not starting, can you confirm?

 

I’ll hafta go back and read through the whole thing again, too

 

will the safety relay do this kind of thing?

 

The starter interlock one would not, but the sidestand one sure could. If it failed closed, was iffy, or triggered improperly it would ground out the TCI and cause a crank/no start. Not sure I've ever seen one do that but I guess it's possible. I'm waiting to see if he confirmed that there is spark when it is not starting. Need that info to move onto next step.

The more I think about it, either being faulty could cause an issue.

 

yes, there is spark when it is turning over and not starting. That's why I am thinking some fuel problem. Right now, it seems to be starting and running fine, although I hav not ridden it. Waiting for the weekend when I have time to get the trailer is needed. I still can't understand why there is air in the fuel line even though it is sloped up and fuel is flowing freely through the fuel line. (same thing happens with my Honda Rebel, but it has never been a problem.)

 

i have that magic bubble too, it's there when i leave and gone when i get back, then it reappears

 

I don't think mine ever goes away, but I'm going to try and see if I can get it to go back into the tank through the petcock with it on prime.

 

Air bubble is normal, even if you can get the tank high enough for the air to rise up into it the bubble will come back eventually as that is the highest point. Fuel will flow just fine. All my bikes with clear lines/filters have it. My golf cart has two clear filters on it lying horizontally, they are barely 1/4 full at all times as there is nowhere for the air to go.

Weird issue, definitely a head scratcher. Check carb bowls for fuel right after it dies? Maybe try a new set of plugs? Long shot that they would all be bad but I had a lawnmower once that was super finicky and after pulling the carb three times I changed the plug, has been fine ever since. Plug looked good and sparked but apparently didn't under compression.

 

Plugs probably have 5-6 thousand on them, but look perfect. I have a plug cleaner so I'll give them a good cleaning and verify the gap and see if that solves the problem. The whole thing sort of spooks me.

 

Common issue on snowmobiles......we all always carry extra plugs with us for this very reason.

 

I meant to replace them altogether, I cleaned the crap outta that lawnmower plug and it didn't change a thing.

It was actually your repeated mention of a "bad plug" that got me to finally try a new plug. I used to think that a plug not firing under compression was BS but I'm a believer now

 

So the pickup coils should be considered. If you lose one pickup coil the bike will not start (assuming the 85 TCI is similar to the 82), but will spark on two of the cylinders, which happen to be the two with the bad pickup. They are known to fail when hot so getting the bike back on the road and maybe carrying a meter to check the resistance when / if it dies might work. Nominal resistance would be 120 ohms +/- 20% and they should be open if checked to chassis ground (engine).

 

Walked out this morning, hit the starter switch and it fired up almost instantly--with no choke. Idled fine. The air bubble is right as the line goes into the petcock and actually gets a little larger when it is running, but I can see fuel passing through the line. Rode it about 6-7 miles, around the neighborhood and then on the highway. No issues at all. Darn--I hate intermittent problems. I guess I will just ride it around town for a couple of weeks to restore my confidence before venturing out on any highway trip. Thanks for all the suggestions.
PS--The bubble still bothers me.

 

hypothetical question. I keep my bikes on a battery tender when in the garage, so each has a pigtail connection attached to the battery. None of them still have the caps that seem to tear off easily. So, if the plug end were to get wet from rain could it short out the bike in some way. I've ridden in some hard rain in the past and never had a problem, but that doesn't mean something couldn't happen.

 

I’d think that to be unlikely for this

 

If it could short out it could short out - rain has nothing to do with it.

 

I have an intermittent problem with side stand switch sometimes not allowing bike to start..but I think it usually prevents cranking...if I recall (62 year old brain cells might be failing).

I also have a permanent bubble in my fuel filter, but it has never been an issue.

 

If there is a bubble in the line or filter there is fuel in it, that's why I like the bubble lol. A quick visual check.