XJ550 won't start when warm

My problem is that my XJ550 won't start when it's warm. It will start if I turn it off then try to start it right away but if I let it sit for about 15 minutes, it just refuses to start. I've cleaned all the connections, replaced the fuse block, cleaned the starter and checked the brushes. I can get a good flow of gas out of the float bowl drain. I can see a spark if I pull a plug and hold in on the engine. It doesn't seem to be flooded as the plugs are dry if I pull them after I've tried to start it. I've checked the impedances on the ignition coils and pickup coils and they are all within spec when cold. They do go a little above spec when warm but I just figured that was the copper wire getting warm.

The bike will run all day long and runs beautifully. It starts right up when cold but just refuses to start if it sits for a little while when warm. Any ideas?

Thanks!

 

Vapor lock,maybe? Come on guys,chime in!

 

Thats odd mine is the oppiset hard to start when cold, but i think that is true of the air cooled bikes.

 

I used to have the exact problem with my car. Turned out the starter would overheat and fail to restart on hot days. It was mounted up against, and behind the hot engine, and wasn't getting any air flow. I had looked into either shielding the starter, or a higher capacity battery, but I ended up with another car before I fixed it.

 

Your ignition coil findings probably warrent a talk with some of the really knowledgable guys here. It sounds strange to me, but then again, I've never tested coils and don't really know what to expect.

How is the idle? What colour are the sparkplugs? When was the last valve adjustment?

 

It purrs like a kitten at idle and the spark plugs are that nice tan color. It does need the valves adjusted and as soon as I get a new valve cover gasket, I'm going to do that but I really don't think that should keep it from starting when warm.

I'm going to try a shot of ether just to rule out a gas problem. I picked up a set of coils on ebay so I'll try changing them if the ether confirms no gas problem.

 

Many weird things happen when the valves are out of adjustment - if you're going to need to do it soon, now might not be a bad time.

I don't think it is a gas problem... but if it were - have you checked your float bowls? Have you made sure there are no fuel line pinches.

Now for why I don't think it is a fuel problem. You say the plugs are tan. It restarts when hot but not warm. If it only restarted cold or warm then it might be possible that it's too lean to restart hot... dunno. As it restarts hot, and starts cold, but not warm - I don't think that points towards a fuel problem.

It might point to a charging issue. If it were hot it would take very little charge to restart. However, as it starts cold (when the most charge would be required) it again doesn't sound likely - rule it out by trying to warm start it immediately after charging the battery, or by using a voltometer.

Why I think it is valves (in my valve newbie status).

When cold the metal is the smallest. I guess that would make the valve opening bigger? For what ever reason it starts. When it's hot, it takes very very little to start the bike. One cough is enough to get the bike spinning fast enough for a sustainable idle and good pull through the carbs. When warm however, the metal is still expanded but not hot... it might be all the difference in the start/not start game.

Adding ether might make it start, but I don't think it rules out the valves - you've just made the conditions for starting easier... if it never ran and ether fixed it then it might more strongly point at fuel.

Now the big if here and the big reason I'm not certain it is valves, is that your coil measurement is tweaking a memory... another one of those when cold they work properly, when hot they don't need to work properly type logics...

So - personally - the two things I'd be looking at - valves and coil. You said you were near doing the valves anyhow so do them earlier... and the coil would require someone like Rick who knows more about that type of thing. Certainly in computer world warm components fail earlier... it would make sense to me that the coils were the issue but I can't tell you for sure so I'd rather have someone else state that as a fact not as my guess.

Woot.

 

Sure sounds like vapor lock to me. Fuel hose running anywhere weird?

On the other hand....can vapor lock occur on a gravity feed system?

 

Not vapor lock but something similar if the tank doesn't vent enough air in to allow the fuel to flow out because the vent is clogged or something. If enough vacuum builds up inside the tank the fuel will stop. That's easy to check by installing clear fuel line to monitor the fuel and opening the cap if necessary to get it to flow.

 

Thanks for the advice guys. Here's what I found out today. Took it out for a nice run over lunch and it ran beautifully. Brought it home, let it sit for 15 minutes and it refused to start. Not even a hint of it catching. Pulled a plug wire and I could see a spark when I cranked it over. Sprayed about 2 seconds worth of starting fluid into the air cleaner and still not a hint of it starting. I really don't think it's fuel at this point. It should have run on the starting fluid if that were the case. I measured the impedances on the coils and here's what I found:
Primary: .27 ohms (orange to red/white) - .28 ohms (gray to red/white)
Secondary: 12.5K ohms (1,4) - 12.7k ohms (2,3)
Pickup coils: 827 ohms (orange to black) - 870 ohms (gray to black) - 1692 ohms (orange to gray, eliminates common)
I'm going to try and start it every hour and when it does start I'll check the impedances again.

The valve cover gasket should be here any day now so I will adjust the valves. I have used ignition coils, pickup coils, and possibly an ignitor on the way so I guess I'll just have to start substituting and see if anything fixes it.

Thanks again!

 

Woot, I think you may be right about the valves. I just tried to start it at 1 hour and it sputtered a few times but still wouldn't start. I pulled plugs 1 and 4 and did a compression check and it was down to 50psi on both chambers. I checked it cold a while back and it was 90psi across the board. I don't want to ride it if the valves are that far out so I will be checking the valves to night even if the gasket doesn't arrive today. I'll let you know what I find.

 

Sanoke:

Assuming the gasket set-up on my twin Seca is similar to the fours, you probably won't have to replace the valve cover gasket if you're careful taking it off.

I didn't even use any sealant on mine, and had no leaks after adjusting my valve shims.

Good luck-
Herb

 

I did my gasket when I did the valve clearances because it was leaking. After pulling everything apart I suspect the problem was the rubberized washers on the cover bolts. If they collapse there isn't enough pressure on the gasket. I recommend you have a close look at them.

 

MiCarl:

Yep, vapor lock can occur in a gravity-feed system. I spent many hot summer days as a teenager on a John Deere "hi-boy" crop sprayer with a little 3-cylinder gas engine. The fuel tank was in the platform about 6 feet off the ground, with a hose running down to the separator bowl and carbs. The exhaust ran under the platform, and fairly close to the fuel tank and line.

On really hot days it would vapor lock, sputter, and die. The only way to get it running again was to remove the separator bowl and let gas flow out until the gas coming out of the tank was cooler.

Then you could go have another hour or two of fun!

Herb

 

When I got the bike, the valve cover gasket was leaking really bad. So much that when I finally got the bike running, it would sit in a cloud of smoke as the oil ran down on the exhaust pipes. I took the cover off and found that someone had kinked the gasket. I used some sealant and managed to get a good fit and it has stopped leaking. That's the only reason I'm reluctant to pull it without having a new gasket. At this point though, I really want to check the valves so I'll adjust and if it leaks, I will just wait for the new gasket.

 

I have this problem with mine occasionally. Next time it does it, try this;
Find yourself one of those squirt-type oil cans. Fill it up with fresh gas. Now go ride, then let it sit 'til it won't start. Now, pull the YICS plug on the right (high) side. Squirt in four or five good squirts of fuel and reinstall the YICS plug (careful not to lose the copper washer or overtorque the plug) Give it some choke (but no throttle) crank it, and see what happens. Mine usually fires right up. I haven't gotten to the bottom of it yet; this is just a band-aid, but it keeps me from getting stranded.
I keep a length of clear tubing under the seat along with a wrench for on-the-road emergencies.
The other thing is, when this happens, I can usually get it to push-start, if I choose to lower myself to that level.

 

Your starting problem sounds a lot like mine, It would fire right up but then when I killed it to get gas or something It wouldnt turn over when it was hot, she would belch out a couple of back fires and still nothing until she got cold then started right up. I changed my battery and its been fine ever since. the thing is the old battery was only a month or two old but it had sat in the freezing weather for some time.

 

Being a newbi to bikes i took the advice that someone on the site gave, Take out the battery when cold it will last longer. now that it is cold in VA i take out the battery evry night when i come home, when starting in the morrining it has plenty of juice. I have left it in over night when cold and sure as the sky is blue the battery did not have the power to start the bike. I also read that in doing this you can run the same batt for up to six years i belive i what i read.

 

So long as the battery stays charged it is fine. When it is charged it won't freeze. Letting a battery stay discharged, however, is the real evil.

 

Well, the valves are way out of adjustment. I think only two were within spec and all the others were too tight. One was so tight I couldn't get my thinnest feeler gauge in. My MotionPro tool doesn't seem to work on all of them so I'm going to try the plastic tie trick, then it's off to the dealer to exchange some shims. Don't know if that will fix my problem but it is certainly something that needs fixed. Thanks for the suggestion Woot!

 

What's the plastic tie trick?

 

Zip-tie valve shim tool
Here's a link to the thread. I used it today and man is it slick! Had no trouble at all as there is plenty of room to get the shims out and in.

By the way, all the exhaust clearances were way too tight and I had one intake that had zero clearance. The odd thing about it was that the shim that was in there was way thicker than all the others. Seems like someone really screwed up adjusting it last time.

 

It may be the valves,kinda weird the way it's doing it,but if you have tight valves(which will always be hanging open)you're compression will be low and starting fluid won't help it because ether needs compression to work properly,I just adjusted my valves on my X,it ain't that bad of a job.

 

Well, it wasn't the valves. They are all within spec and it did the same thing today when I ran it. I finally figured out what the YICS plug was and tried your suggestion of squirting fuel in and it did start. It had been sitting for almost an hour so I'm not positive that did it although I tried starting it before I added the fuel and it didn't. So, I'll try it again tomorrow and see if it works at 15 minutes. I found a link talking about leaks in the YICS system causing it to be hard to start. Any chance my problem could be the YICS system?

 

My bike was smoking trough the pipes, burning oil and I also had a gasket leak. How can this be possible?

Oil comes out of the engine and gets inside the chamber just because of the valve cover gasket?

How do I check the valves?

I also have problems starting my 83 XJ750 MK, where is the YICS plug?

 

I will look in the Haynes for the valves.

Thank you

Gene

 

This is regarding the "plastic tie trick":

A piece of #10 AWG stranded insulated wire works real well, too. You just take a piece about 8" long, kink the last half inch a little and insert it through the spark plug hole and into the valve gap.

The advantage of using the piece of wire is that there is no chance of it breaking and falling into the cylinder, like a plastic tie.

I had to snip off the end of the wire I was using halfway through due to compression of the end, but other than that it worked SWEET.

 

Well, the only "part" in the YICS system is the o-ring between the cylinder and the head. My leaning would be more towards the boots between the carbs and head. You can check this for leaks as follows;
Run the bike and warm it up. With the bike idling and enrichener ("choke")off, spray some WD40 on and around the boots. If the idle picks up, chances are you have air leaks. If it remains unchanged, they're probably OK.
At least you know how to get it started, in the mean time!

 

Well, the only "part" in the YICS system is the o-ring between the cylinder and the head. My leaning would be more towards the boots between the carbs and head. You can check this for leaks as follows;
Run the bike and warm it up. With the bike idling and enrichener ("choke")off, spray some WD40 on and around the boots. If the idle picks up, chances are you have air leaks. If it remains unchanged, they're probably OK.
At least you know how to get it started, in the mean time!

 

At this point I think the coils need more investigation... too bad it wasn't as simple as the valves but now they're done and you don't have to worry about them for another few thousand miles :-/

One other quick question... have you tried starting the bike on prime when it is warm?

 

Yes, I tried starting with prime on and today I tried Captainkirk's method of squirting gas into the YICS chamber and that didn't work at 15 minutes after I shut it down. I'm leaning towards coils now too. I've got some on the way so I'll start substituting and see if that makes any difference.

 

Still a mystery. I tried something new today. I put a temperature probe under the carbs and measured the temperature after it had sat for about 15 minutes. I read about 140F. According to Chevron, about 30% of the gasoline will boil at that point. Bear in mind that I live at 6,000ft above sea level and we are running on winter gas with 10% ethanol. I could hear bubbling coming from the carbs and when I drained gas from the float bowl, there were bubbles in it. I then took a fan, turned it on full blast and aimed it at the carbs. After 10 minutes it started right up. I remember danno suggested that it might be vapor lock. Any one had a similar experience?

 

hrm... still - if that were the case, letting the bike sit on prime for 1 minute before cranking should solve that problem... the vacuum from the intake should be more than enough to overcome what little air is in the lines, and the fuel will flow very easily on prime, even without vacuum.

If we follow the air lock theory through then check any vent lines...

 

high perf 4 stroke bikes have a "hot start" lever to restart after they've been
hot, i think it richens the mixture, dosent make sense to me but thats what i was told
i think its coils,try blocking that heat thats coming off the engine and heating up the coils
you said it starts if you try right after you shut it off (the coils are still cool)
slide some cardboard over the engine to block the hot air from the coils
good luck

 

Maybe I didn't leave it on prime long enough. I'll try that tomorrow. I'm pretty sure it isn't the pickup coils because the fan wouldn't have cooled them off any. It could still be the ignition coils. The used ones arrived today so maybe I'll try switching them just to see if it makes a difference. The thing that puzzles me is I can see a good spark when it won't start. When I tried CaptainKirk's method of squirting gas into the YICS chamber it immediately boiled away. That's part of what's got me thinking it might be vapor lock.

 

Sanoke - you've made a good point there... give it a whirl and see.

What does your fuel line look like btw? is it in good shape?

 

The fuel line is brand new. I replaced it when I rebuilt the carbs. I had a shutoff valve that I put in line but I've removed it thinking that maybe it was part of the problem. Didn't make any differance.

 

Putting it on prime didn't help. I rode around for about an hour and a half and just left it on prime when I parked it. Same thing, 15 minutes later, would not start. An hour later and it started up. I swapped out the ignition coils last night and that didn't make any difference. Guess I'll try the pickup coils tonight.

 

Ok, I'm going to take you down a different track.

Based on what you have said, the fuel may well be boiling at temp.

The answer to me is to work out why the engine gets hot enough to boil the fuel.

My 550 runs fairly hot as well but it is old and tired. But it never gets hot enough to boil the fuel.

Have you checked the valve clearances. There's a twofold reason for this suggestion.

1. If they are not right it can contribute to temp increases.
2, If they are too tight it can reduce the vacuum sucking from the carbs which means it will be harder to start.

Altitude can also play a factor. Is it running standard jets? Jets should be increased to compensate for altitude otherwise it may run too lean.

If it's lean it will run hotter.

Try a bigger Main jet or raise the needle a notch to see if that helps.

Also check oil pressure. Not enough can cause heat generation. Does it run an oil cooler?

I have followed this thread from creation but due to an aging memory some of my suggestions may have been covered already.

At the temps you are claiming I think it is important to work out why it runs so hot, particularly in winter, and that may solve your hard warm starting problems.

Cheers
HG

 

altitude goes up mixture gets richer

 

Quite correct. Always been at sea level so never had the problem. Knew I would get it backwards. :lol:

I still think heat is the main issue though. Do a WOT plug chop and see what they run like at speed. If it is running lean then it can be adjusted.

I re-read back a page and noticed you had done the valves. How was the cam chain looking. Since the timing is fixed the only thing that can affect it is a stretched chain.

Have also seen a similar problem with a kwaka that wouldn't start when hot. Lots of things tryed but the problem turned out to be an ignition pickup.

 

The cam chain looked great. It didn't pull off the cam gear hardly at all. The bike only has 15,000 miles on it so it's basically sound. Good suggestion on the WOT plug check. If changing the pickup coils tonight doesn't do it, I'll try that next.

 

I wonder if the fuel is boiling and flooding it?

Agreed though, they shouldn't be getting hot enough to do that even at altitude - especially in winter.

 

Any way of getting the bike down to the springs. I would like to tackle this problem with you. Just by chance, did you use standard car fuel line when you replaced the fuel line. I agree with the others on the fuel system vapor lock. Could there be back presure on the petcock? Maybe a gummes up petcock o-ring. Then back pressure put on it by the fuel system or the new thinner fuel feed line causing it to stick in place until the pressure is relieved by the engine cooling off.
Sounds like a fun, yet anoying problem to solve. Shoot me a pm if interested in getting together and putting a couple of on site minds on the problem. We could balance the carbs while we are at it.

 

The "Vapor-lock" can be "Air Bubble Lock"
If the Inline Filter is an irregular one or Large diameter; an air bubble in the filter chamber will act on the gravity flow.

There's only three things it can be:

Fuel, air and spark.

See if the bike will act right if you run it off a "Tune-up Aux. Fuel-Supply Source" for awhile and do some Start-up Tests and go from there. If the Clunk-Test is good and fuel-supply checks-out; tune it for "High Altitude Running" or something close to that ... as the base for finding the best performance we can get.

Write down what everything is set-up at and adjusted too, at the moment; and keep track. You're at where you cannot make multiple adjustments and expect to know what did what, and what to do next!

 

Had this problem with a Honda XR500RC. Started fine cold, but nip when it stalled hot. Had to hold the throttle wide open and kick it 3 or 4 times then it would start, fuel boiling and flooding it, common problem on a few old bikes. My Suzuki DR250Z was a "first kick" start all the time

 

Thanks for the offer. It's really just an annoyance at this point. I have two other bikes that I can depend on and this is my winter project bike. It starts instantly when cold and runs beautifully as long as I want to ride. It's just that if I stop for more than 5 minutes, it's going to be an hour whether I want to wait that long or not. I did use automotive fuel line when I replaced it so maybe I'll stick the old line back on just to see if there is any difference. I've not ColorTuned or synced the carbs yet and that's on my list. RickCoMatic had a good suggestion of trying it on my tune up aux tank to rule out the petcock. Hired_Goon suggested a WOT plug check so I'll give that a try too. I also want to try running a lower octane gas just to see if that makes a difference. If none of that pans out, I'll get in touch. Thanks!

 

Ok, as many of you surmised, it's definately not ignition. Last night I swapped out the pickup coils, checked the timing and today it did the same thing. That means I've changed everything related to the ignition as well as cleaned the starter and all electrical connections and it still won't start after 15 minutes. I found a spot to put my temperature probe that was in near the center carbs and at 15 minutes the temp was 120F. Not all that warm but I could hear what sounded like gas bubbling in the carbs.

Did something different today that seemed to help. I left it on run then went back about 20 minutes later and switched it to prime. I could hear gas running into the carbs so I waited until they stopped filling. I was then able to get it started by holding the throttle wide open. I don't think it is a petcock or fuel line problem. I think the gas in the float bowls is boiling away. By waiting and then filling the carbs, they cooled down enough so that it ran. There really isn't much space at the bottom of the carbs to keep them from getting heated up by the engine. When the bike is running, the gas evaporating in the carbs keeps them cool as well as the airflow from moving. I'm thinking that the combination of higher altitude, winter gas and high octane are just causing the gas to boil out after the bike is shut down. I want to try a different brand with a lower octane (higher boiling point) and see if that makes a differance.

As a side note, I used to have a Toyota Landcruiser that had the exhaust pipe running close to the gas tank. In the winter, if we happened to have a warm day, I could hear the gas in the tank boiling. It only seemed to do it on winter gas because even on a hot summer day, it didn't do it.

 

re: Octane. I'm not sure that a lower octane has a higher boiling point. I do know that higher octane resists detonation more than lower octane. I'm only guessing from that, that higher octane would as a result have a higher boiling point. Substances are strange so you could indeed be correct...

If the engine is getting that hot, I really am wondering the same thing as Rick - are you lean.

Very strange... :-/ sorry I couldn't be more help.

 

I'm sorry! But, I don't think that is possible.

You'd have to be at such an altitude for that to happen; that the only nearby gas station would have Sherpa's working there ... full-time!