XJ550 won't start when warm

if your gas is boiling in the float bowls the vapor is condensing on the next cool thing it touches, like the airbox then it might drain to the crankcase or maybe run back thru the carbs and down the intake and flood it
it seems like four bowls or even four half bowls of gas boiled to vapor is a very dangerous situation and besides it would stink to high heaven

BE CAREFUL

 

if your gas is boiling in the float bowls the vapor is condensing on the next cool thing it touches, like the airbox then it might drain to the crankcase or maybe run back thru the carbs and down the intake and flood it
it seems like four bowls or even four half bowls of gas boiled to vapor is a very dangerous situation and besides it would stink to high heaven

BE CAREFUL

 

Do your carbs still have the heat shield attached under them?

Not sure if all models do but my 550 definately does.

 

The intakes are hotter than the carbs so it won't run back into the engine. It does stink a lot. Acutally all three of my bikes do after I shut them down. What I know is that 15 minutes after I shut it down from a good run, I can hear bubbling in the carbs. I don't see any fuel running out anywhere and if I try to start it, the plugs are dry. If I try squirting fuel into the combustion chamber, it immediately boils off. The same is true if I try to put it into the YICS manifold. If I wait 30 minutes and put it on prime, I can hear fuel running into the float chambers and after they fill, the bike will start if I hold the throttle wide open.

I do have the heat shield on but with the bike stopped, I can't imagine that it does a lot of good once it heats up. What I'm going to do today is take my XS850 out for a spin then measure the crankcase temperature after I'm done. If it's a lot cooler than my XJ550 then I need to see why my XJ550 is running so hot.

 

An air-cooled engine, running that hot, must be on the edge of its self-destruction by running far, far too lean. There is a host of catastrophic failures linked to running too lean and over-heating a small engine.

Piston melt and weld-through. Burned valves. Cracked and warped heads. Total seizure.

To begin getting that bike tuned-up -- you need to chart ALL the Jetting. Fuel and Air. You're likely to have to do some Mod's. But, it all depends on what's in there now.

By the time you get your carbs dialed-in and that bike running sweet ... you'll wish the carbs were attached with Velcro.

 

Just thought I'd let you know where I'm at with this. I checked the jets and they are stock. The needle valve only has one groove in it so it can't be raised or lowered. I color tuned the carbs to adjust the idle mixture. I also switched to 87 octane gas (was running 91). It will now start at 15 minutes if I turn the petcock to prime, give it full choke (enrichment) and work the throttle. As before, the bike starts right up when it's cold (with full choke) and really is running great at this point. I'm just going to put some miles on it and see if anything changes.

Thanks for all your suggestions!

 

yeah my XJ550 started doing this the last two times I rode it. Kind of a pain in the butt, but I can get it started if I twist the throttle a bit while cranking...so it doesn't strand me.

 

My 81 xj550 has done this for years, It would always start right after I would shut it off. But if I waited a couple of minutes, i would have to crank the heck out of the starter to get it to run.
I've owned this bike since 83, I can't remember a time when it hasn't done this.

 

the XJ550 I had would do that also,if you started it within probly 5 min of shuting off it would fire right up,but if you waited much longer it wouldnt start,wait about 20 min or so and it would fire right up :?
I could dribble a few drops of gas in a couple cylenders,just enough to make it fire once and she would fire up.
it was kinda wierd!!!!

 

Finally solved my problem. Through enough experimenting I determined that it was vapor lock that was causing the problem. I tried insulating the bottoms of the carbs and that helped some but didn't fix it. What I finally did that eliminated the problem was to add a fan.

If I'm going to stop for a half hour or less, I just turn on the fan. When I come back, the bike will start right up.

I want to add that I've put over 3,000 miles on this bike so far. It still runs like a top and other than the vapor lock problem, it's been extremely reliable. I'm guessing that the vapor lock is related to living at 6,000 ft. and how close the bottoms of the carbs are to the engine case.

 

I can't find the Thread on another site ... but, I distinctly remember helping a lad at High-altitude get his 600 starting better by experimenting with the Air Jet.

We substituted the stock Starting Air Jet with one out of a (not sure but think it was a XS650 ... might have been a XV920 ... anyway, is several bumps-up) bigger bike.

When it start working, he quit the experiment.
I was going to have him drill the Jet out ... one Number at a time until it started.

You might give the DynoJet People a call ... they just might offer a High-Altitude Kit that their research shows is right for your bike. They might not have it listed any more ... but, it might be the same kit that they market for the Dirt Riders and 4-Wheeler folks.