83 xj650 will not start when hot

Hi there , I am in search of help to fix this problem .. Alot of help lol . I have a 83 xj650 upgraded exhaust , carbs rejetted for the pipes , new coils , etc etc and the problem is , you can start it run it , and it runs like nothing is wrong with it . Perfect .. When the bike gets hot after 30 minutes of riding , it loses idle and dies out and will not start ... Any suggestions ?

 

What is ... "etc etc"?
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Does the Bike get "Too Hot" ... that can be a problem.
There's a LOT of reasons a Bike won't start hot.

Make sure the Vacuum Line fom the Manifold to the Petcock is ACTUALLY Vacuum Line. Other Hose substituted for Vacuum Line will get hot ... collapse on itself ... close-off the Fuel Flow and the Bike runs out of Fuel.

You might have to do a Square One Tune-Up.
Compression
Valves
Ignition Troubleshooting.

How long does it run before it shuts down?

 

VALVES.

 

Hi there ,

Well the bike is a 1983 xj650

the bike will cold start perfectly and run and idle like a dream boat

after you ride the bike for 10-20-30 minutes the idle dies down from 1050 1100 , and just dies out ..

Mods... Jetted carbs , aftermarket exhaust, new battery , new coils , new starter , new starter relay.

The carbs have been sync'd and jetted for the pipes , the bike ran like a dream last year and this year the first couple of months it was great , this problem started happening about 2 months ago ...

So I know the carbs are getting gas , you can try to start it until the battery is almost dead and just reaks of raw building up.

If you let the bike sit for a couple hours it will start right back up and run beautiful again .. I hope all this information helps
I ran Ohm and resistence tests on electrical it all checks out
I did

 

See I am assuming it is the valves to be honest, you can push it in the highest gear about 50 feet and she will start right back up like there was some sort of vapor lock

 

How do the plugs look? A lean idle mixture will make a hot engine real hard to start.

 

the plugs look good they have a minor carbon build up but nothing showing them that the bike is running lean ..

 

you need to diagnose the bike when the problem persists. your probably not going to find anything when it's running like a champ.

you might have an electrical issue that acts up with heat. OR, as rick suggests. vacuum line caving in so no vacuum is going to fuel switch.

if it's a mechanical issue. the problem SHOULD be more permament regardless of heat factor.

think of it like this-----

car runs fine when cold. dies with heat. 2 common problems. failing fuel pumps usually run good when cold and quit as they warm up. ignition module would be the second most common problem that quits with heat. ford was notorious.

you get the idea????

 

When the bike dies have you checked to see if you still have spark at the plugs? Start the process of elimination, Got fuel? Spark?Make sure all the other stuff is in good order, fuses, valve clearences, carbs.

 

I did check all those things as a matter of fact , the spark was weak so , I checked the coils and determined the coils were shot , 1 coil was open it wasnt working period , so I replaced them , and the plugs are nice and brights, the fuel situation yes , its loading up in the carbs , fuses, relays, carbs have all been checked and tested for ohms and resistance , all BUT BUT valves ... so valves is the next step .

 

Should have been one of the first steps, could have saved yourself some headaches I bet...

This may help http://xjbikes.com/Forums/viewtopic/t=14827.html

THEN you can re adjust the carbs.

 

thanks for the link , and as far as the first step , not for me , I would have never ever assumed that the valves could do this .. trlays , coils , switch and things of that nature , sure , but valves I never knew .

 

Valve clearances get tighter as they wear; the valves pound themselves into the seats. If they get TOO tight, the valve stops closing fully especially when HOT.

There could be a lot of other contributing factors like float levels, etc., but you can't even begin carb tuning until you're sure of the valves.

 

Just a quick question .... I noticed the xj650's welll turbo edition has heat shields up where the valve cover is on a different bike .. Now do all these xj650 are they supposed to have that on there ? It sits right up in front of the spark plugs and acts as a funnel to cool the engine as you ride ..