XJ650 that runs great until it suddenly dies

New guy here with an 1981 XJ650 Maxim - came with pod filters and a rejet but otherwise stock. Bought it a couple months ago with an intermittent "ignition issue" that appears to be getting worse and I'm not sure what to do. It would originally "shut off" (still have have electrical power) a few miles into a ride. It would restart right away (I could pull in the clutch, hit the starter, release the clutch and take off again without even downshifting). I replaced the fuel cap (the main rubber seal was at the end of life) since my google/xjbikes searches led me to think it might be the vent valve. and it ran great for a couple weeks. Then it died like it had in the past. Quick restart and I was off. Then a few days later it died and took several minutes of starting before it fired. Most recently I was getting ready to go on a ride and while it was idling it died and didn't want to restart. I started it up a few times in the garage now (since it old takes 7 minutes to stall after a start) and I notices the rpms climb (maybe 200 rpm) shortly before it dies, kinda like It's leaning out (I'm fairly confident It's jetted a bit rich) and getting a more optimum air/fuel ratio.

What I know:
-Fuel filter is installed on the fuel line but doesn't appear to have any junk in it.
-New ebay fuel cap and ignition switch installed made from the finest chinesium
-Plugs have a high amount of of deposits on them (unsure if its worth it to replace them before I figure out this issue)
-Battery voltage is ~11.5V off and ~14V running around 2k+ rpm (choke on)
-I have yet to do any riding in the rain and the bike is stored indoors

Any help would be greatly appreciated!

 

did you ever try with the gas cap open and fuel valve on prime? i don't trust those chinesium guys.
the rise in rpm could be it getting lean because it's running out of gas. replace the vacuum line from the fuel valve to the vacuum port, usually on #3 intake. it could be bad but the prime setting should take care of that.

 

Valve clearances are in spec?

 

Try the good old fuses. If it still has the original fuse holders replace it with a new blade style fuse box.

 

Thanks for the replies guys!

I've popped open the gas cap a few times when it's died and haven't heard any air rushing in. However, I haven't switched to prime when it has died. The vacuum line also looks to be in good condition, if anything a bit soft. Could it be pulling enough vacuum at 2k rpm to collapse the hose?

The previous owner had done a valve job recently and it runs great while running so I don't think that would be the issue (more intensive than I want to do right now).

The fuses also aren't stock and have been replaced with blades (forgot about that - oops)

 

Have you determined if the bike dies from lack of fuel or losing spark? I would put money on a electrical problem

 

Never trust what the previous owner has done. Check the valve clearance for yourself.

 

Not very intense at all (and it is a stepping off point before trouble shooting anything else):

http://www.xjbikes.com/forums/threads/airhead-valve-adjustment-with-pics.14827/

Read the article, try it, ask for help if you need it. There are a lot of good people here willing to walk you through whatever it takes to make your baby reliable.

 

Valve clearances will be checked, but I having troubling seeing how valves would cause the bike to go from running great to dead.

I switch between thinking its spark or fuel daily, sometimes hourly. There's been a few times I've turned over the engine after it dieing and it backfires (which points to fuel but no spark). However the rpm rise/leaning out sounds like a fuel issue.

Another thing I should mention. The past few times it has died (I've done some trial start and idles) shortly after there is a "kshhhh" air releasing/venting sound from around the engine/under the tank. Could that be the vacuum line for the petcock un-collapsing? Is a collapsing vacuum line something that happens? It's too late for me to do another trial run (I try to keep the neighbors

 

Huh, I wanted to end that last post with "happy)". I might be getting a bit tired...

Anyway, that is a really nice tutorial on checking valve clearances - Bookmarked!

 

As the engine warms up to operating (or higher) temps, metal expands, and the valve clearances thus get smaller. Think of railroad tracks, those expansion joints are there to allow for "hot" metal (rails) to expand and not buckle......... Thus if clearance are too small to begin with (when cold), they just get smaller and smaller as the engine warms, and in extreme instances will close their gap to zero (or less) and thus the valve(s) stay open all the time = engine dies. The "valve job" that the previous owner did, if it involved lapping the valves, that procedure automatically results in reduced clearances.

Fuel hose resists expansion, vac hose resists collapse. If someone used fuel line (of an appropriate size) in place of the vac hose, then yes as it warms up it could collapse. That's why people suggest setting the petcock to the PRime setting and test-riding. The PR setting doesn't rely on engine vac to allow fuel flow, thus a collapsing hose won't affect the engine fuel supply.

 

This also could point to valve clearances being reduced to zero after the engine warms and the combustion event escaping thru an open intake or exhaust valve.

 

Did I say valve job? (Dang it, I did) I meant he re-shimmed the valves. At any rate it, it looks like I'm picking up a feeler gauge and popping off the valve cover this weekend to grade the POs work...

 

ohm out your coils primary and secondary as well as your spark plug caps.
also ohm out your pick up coil
this was the same symptoms my 550 developed ended up with a blown resistor in the cap and a failed pickup coil
when you test the plug caps (they unscrew from plug wires) trim about 3/8 inch off the plug wires of before reinstalling them
.secondary of coil is the spark plug wires measure end to end of wires fron same coil pack.
you can test the coil primary from the right side connector of the tci box. if out of spec test from connector at coil.
should be orange to red white wire, then gray to red white wire.
pick ups are tested from the left plug in your tci box there should be a gray wire and an orange wire as well as a black wire test ohms between orange and black then between gray and black.


Pick-up coils:
1980-81 XJ650 Maxim and Midnight Maxim: 700 ohms +/- 20% = 560 ohms to 840 ohms acceptable range
Ignition Coils:
Primary side (input from main wiring harness):
2.5 ohms +/- 10% = 2.25 ohms - 2.75 ohms acceptable range
Secondary side (spark plug wires, without their end caps):
11K ohms +/- 20% = 8,800 ohms - 13,200 ohms acceptable range
Spark plug caps:
5K +/- 20% = 4,000 to 6,000 ohms per cap acceptable range
Spark plugs:
0 ohms per plug

#13 are coil packs
#14 is tci unit
#15 is pick up coils

and the disclaimer
same symptoms do not mean same problems

what you discribed was same symptoms i had
just another place to look

 

I checked the pick up coils and they came out 600 and 640 ohms (good) and the ignition coils primary side came out to 2.6 ohms for both (good)

For the pick up coils, reality strayed a little from that diagram. Instead of having the black w/ white stripe write I had a brown wire which went one of the pickups and the black wire went to the other.

I'm about to head to a parts store for a vacuum hose fit the petcock and feeler gauges although I will be busy the rest of the day, so I probably won't be able to do any more trouble shooting.

 

Wouldn't it take a few minutes for the valves to cool if the clearance was the problem.
But then again if the tank vent were the problem it should take some time also.
Maybe talk mean to it, threaten it with a big screwdriver, slam the seat and kick the tire
Works for me

 

Heh, maybe I'm doing too much sweet talking and that's my problem.

Had a few minutes to look into it. Put a new petcock vacuum line on and started it up. Idled for maybe 3 minutes and died. So, I set the petcock to prime and opened the fuel cap. Still wouldn't even attempt to fire. I think I'm checking valve shims this weekend...

 

could one of those safety relays cause this, i don't know i don't have any. how about a solder joint in the TCI. you could unscrew the TCI and let it hang by the wires so it didn't vibrate. it's a long shot but it's free and easy

 

Valves need to be checked but out of spec valves won't make a bike quit after a few minutes of running. They will make it run rough and impossible to get a proper idle along with other things.
Your bike cutting off suddenly points to some sort of electrical issue. Next time you are running it and it quits there are a few questions you need to answer. Run it again and have a meter or test light handy to find out where the problem is.
1- did it loose spark or run out of fuel? Which one? Loss of fuel is easy, what is keeping it from the carbs?
2- if you lost spark that's a little more difficult. Is it gone from loss of 12 volt power( fuses , switches, bad connections)
3- if spark is gone and you verified that there is 12 volts to the tci them why . Is there signal from the pick-up coils? Are the ignition coils getting a signal to fire?
Look over a wiring diagram for your bike and see what might cause it to loose power to the TCI. Clean and test whatever switch supplies power to the TCI. It might be a simple relay or dirty switch.

 

Started up the bike tonight and it ran fine. Took it for a quick ride and came to two conclusion:

It's too cold outside for me now
It's too cold for my rear tire that I wasn't paying enough attention too. It is currently sitting off the bead... oops...

 

Tires (generally) require sufficient air pressure. Get your spoons out.

 

After checking the valves shims, I have come to the conclusion that I need a more precise feeler gauge. The one I got only goes down to 0.152 mm. So here's the results of trying to using what I had:



Cyl~~~~~1~~~~~~~~2~~~~~~~~3~~~~~~~~4

Exh.~~~.203~~~~~.152~~~~~~.152~~~~~~~0

Int.~~~~.152~~~~~~0~~~~~~~~0~~~~~~~.152


So Exhaust for cylinder 4 is a bit tight (but how much is unknown) and Intake for cylinders 2 and 3 *could* be out of spec but everything appears to be good enough that it shouldn't be causing problems. Of course I need to get a better feeler gauge and try again to truly verify everything

 

Get KD tools 2274 METRIC feeler gauges. That way you don't have to remember to round the measurements you're getting from the SAE gauges you're using.

And keep at it. You're making progress.

 

I'm in agreement with dragsta. I'm currently fighting a somewhat similar condition and am narrowing it down to a carb needle and seat. I learned a lot by removing the four rubber air box to carbs tubes. With the engine running you can look for the presence of raw fuel in the carb as well as quickly note a back fire. I also cut a piece of cardboard from the back of a note pad into a mini ping pong paddle shape so I could block off the intakes of the carbs one by one. It does a power balance test without stressing the ignition.

 

exhaust 2 an 3 are tight too

you can order the KD tool Kmoe suggested at most auto parts stores. the right tool makes the job so much easier

good call on that

arn't you glad you checked them

knowing whats right eliminates it as being a problem.

cheap enough fix to rule it out as the problem

 

Exhaust probably aren't tight. All I know is that they are somewhere between .152 and .203. I now have the correct feeler gauge, but haven't taken the time to pop the valve cover off again.

I did find my fuel line was mildly kinked just before it went onto the carb. I didn't think that it was that bad, but I cut off that section since that seems to be the most likely cause at this point.

When I put everything together, the battery was too weak to get fuel drawn through, and I was under a time crunch so I couldn't mess with my charger. Since that day it's been rather cool, so the bike got stuffed in the front of the garage so both me and my housemate could park in there. Once I get to winter break, I'll try to get the thing to fire again.

 

I just read all the way through again and all I keep coming up with is a carb / floats issue or the fuel supply rail is clogging up.... Seen that enough time too--

I 100% do not think its a valve clearance issue.

But make sure you have plenty of gas in the tank..... It wouldn't be the first time that all starving issues were solved by filling up.....

Dave

 

We are in the middle of a heat wave here in MN (above freezing!) so I took some time and got fuel drawn into the carbs to get her running again. Took her out for a ride and got a little over 2 miles and it stalled with a backfire. Started up within a minute or two and so I nursed her back home. At idle she was fine, but any other time there was a fairly regular miss (like one or two cylinders would miss 10-25% of the time). Got back home and pulled out my infrared temp gun and checked temps. The outer cylinders were both about 135 degrees F and the inner two were about 115 degrees (ambient is about 40 right now). Does that sound like a coil pack?

 

Could be ignition-related. Try running the bike in the dark and look for arcing. Also try poking around the ignition wiring (TCI, coils, HT leads) with a wooden dowel (non-conductive) and see if you can aggravate the situation (pointing to a bad connection, broken wire, or bad insulation). Similarly, you might try tapping the TCI itself to see whether that causes a miss.

 

Just took a multimeter to the plug caps and I'm not sure what to make of my findings.
[Cylinder ohms]
1 7750
2 5700
3 5640
4 8430

Are cylinders one and four supposed to be that high? Based on what was posted by XJ550H on page 1, all the caps should be between 4k and 6k. I suppose I should check the spark plug wires, but how do I do that? Stick the probes into the paired wires?

 

when you check the secondary HV side of the coils, the wires are tested. But resistance check isn't 100% for sure, things can go on in the coil while running that your meter just can't duplicate.
It's a good place to start though

 

So, going through the plug caps, my resistance reads as follows:

Cylinders 1 and 4: 29,400 ohms
Cylinders 2 and 3: 22,600 ohms

So subtracting out the Caps I already recorded, that gives:

Cylinders 1 and 4: 13,220 ohms
Cylinders 2 and 3: 11,260 ohms

Is it just me or do cylinders 1 and 4 have a lot more resistance than they're supposed to?

 

The caps are all supposed to be 5K Ohms, IIRC. Definitely odd to have such high values on 1 and 4.

For the coil itself - measured without the caps - the question is whether that number stays steady, or starts varying as you move the wire around or tap on the coil body. If it varies, there's a problem in the coil.

 

I measured with the caps on (sue me ) and the resistance stayed rock solid while trying to play jump rope with the wires and knocking on the coils. So I'm open to ideas...

 

i think those caps come apart, they unscrew from the wire. while they're off look up inside where the plug goes for a screwdriver slot. if it's there unscrew it and a resistor should come out.
clean it up, test the resistor. then cut 1/2 inch off the wire and put it all back. retest

 

There were no screwdriver slots in any of the caps so idk.

Since several people have said it's a fuel issue, and there was an inline brass fuel filter, I went ahead and replaced it with a less restrictive screen. Tomorrow I'll go start it up and see if that changed anything.

 

you need to replace the spark plug caps you are having the same issue I had early this year cap resistor shattered and my pick up coil failed.
do not know if it was a failing pick up that caused the resistance problem or failing resistor that caused the pick up to fail, or if it was a coincidence. i would ride about 20 miles then bike would stall out as i got in drive way start up 20 minutes later.
then i could ride 3/4 mile and stall out in the same place on the way home. then it went completly
out of spec is out of spec
i chased it as a fuel issue until it failed completly

 

cut back the wires. if in spec you good on the coils
11K ohms +/- 20% = 8,800 ohms - 13,200 ohms acceptable range
your readings are in spec . in a perfect world coils would be the same value you could get another coil pack to see if you could get a better pairing

 

I had a 1980 and a 1981 both exhibit the same symptoms. Both had the black label TCI and in both cases a TCI swap fixed the issue. You can use the red label TCI but you should make sure you use a pickup coil rotor from the same machine.

 

While a faulty TCI is a possible cause, it is not the first thing to swap out.

 

I keep on meaning to giving an update. I did go ahead and order a pair of NGK spark plug caps. They should be here Monday, just in time for some snow. Not going to replace anything else until I can do a test ride with the new caps (whenever that may be...).

 

That's a given. The first thing is to determine which of the big 3, fuel, spark, or compression is being lost. But if there is a spare TCI available it will save you from running down a bunch of rabbit holes and has a whole lot higher chance of success than a valve adjustment.

 

I'm still staying with the fuel idea. Put the petcock on PRI, start the bike and go for a ride... See if it still does it. If not, the petcock is the likely culprit. If it still does it, you've possibly eliminated that as a cause

 

Zaxbys said, "I measured with the caps on (sue me ) and the resistance stayed rock solid while trying to play jump rope with the wires and knocking on the coils. So I'm open to ideas..."

+1.

Gary H.

 

When it dies, does it just suddenly go completely dead, like it would if you hit the kill switch, or does it bog a bit, struggle more, and then die? The former is more likely spark, while the latter is more likely fuel.

 

Alright, so to answer sqlguy, it would normally just quit with no warning, or a couple seconds beforehand there would be a slight stumble for a split second.

Anywho, temps for up to balmy 40 degrees, I took the bike out to
A. So if the new plug caps had an effect
B. Mess around with the petcock.

After a minute or so of riding side streets (going back and forth on a 3/4 mile stretch with a 30 mph speed limit), the bike started missing again (remember, the last time I took it out, it suddenly died, and once I got it restarted, it would miss on the mile ride back; never had a missing issue before) so I turned the tank to prime, and 30 seconds to a minute later the miss went away. I did go back to the normal setting and took it a mile out of town (hitting 60 mph) and had no issues after that.

So it sounds like I need to rebuild a petcock. Can someone point me towards a thread showing me what needs to be done?

 

It seems to me that the vacuum line is collapsing when it gets warm. Go buy a length of real vacuum line (most of the time people just put on whatever fits; real vacuum line is thick-walled). That should solve your problem.

Petcock rebuild link, if you still think you need to do that.

 

Already put a new vacuum line on it Thanks for the link!

Edit: that link doesn't work for me.

 

Try this:
http://www.xjbikes.com/forums/threads/rebuilding-the-yamaha-vacuum-fuel-valve-w-pics.25058/

 

Yus! Thank you!