XT 600 wont start but runs great

[I2SMf245]

I have a 1993 XT600E 3TB that wont start. If i jump start the bike with a car and turn it over for a while and get lucky it fires and starts. It runs really well while its on and idles with no problems. but as soon as i turn the bike off it just wont start again on the electric start, even when the bike is warm.

I have cleaned the carb halves twice by hand with carb cleaner blowing every jet and cleaned it in an ultra sonic cleaner. intake boots are almost new with no leaks. I have checked the valve clearances twice (intake between 0.05mm and 0.10 and exhaust between 0.10 and 0.15). I have replaced the ignition coil and sparkplug cap. (primary resistance is 3 Ohm and secondary is 15 kilo ohms with sparkplug cap). New sparkplug with a Strong visible spark. pickup coil is producing 0.2-0.3V while cranking.

Thought it might be an auto decomp issue and took the valve cover off only to realize the bike doesn't have an auto decomp.

Sometimes the bike back fires through the carbs or exhaust when starting which makes me think it has to be ignition timing during low starting RPM. It wont even start on starting spray. The bike had a little trouble starting before the winter but now after the winter it just wont start on the starter motor. I took the bike for a ride in the woods and accidentally killed it twice but it started easily by bump starting it down a hill.

I've been trying to fix the issue for weeks and i can't find the cause of the problem. Through running in circles looking through forums and chatGPT it seems it could be the CDI but the only ones i can find are quite expensive for something that might not even fix the issue.

Been feeling frustrated and annoyed at the bike as it seems so weird that it idles, runs, and bump starts easily but refuses to start on the electric start. I've only had the chance to ride the bike a few times since purchasing it last fall and i am so eager to ride it because i had so much fun with it.

[charliext1vj]

A lot of information there but I can't see what your compression test results are?

If you have a strong spark and its not igniting on easystart then in my opinion it must be compression related (or possibly very bad timing like a sheared key) or sucking in a lot of air.

Compression test dry and wet first.

Inspect your carb boots well looking from separation close to the mounting bolts.

Then check your alignment marks for camchain.

I would also drain your oil - if the carb was doing its job properly I expect you may have a lot of petrol in the oil and have washed the bore.

If it is backfiring I would expect its sucking in a lot of air...hence check your carb inlet boots - I had them split from the rubber to the metal on a new pair and you could not tell until they were removed.

Some help is better than no help??

Good Luck

[Barryn]

Great start on the diagnosis.
Three things in my mind on something like this
Fuel
Spark
Timing

Did you replace the fuel inlet valve and filter?




It can get blocked.

Then set the float height with the new float valve.







If you are getting a spark you should be fine. BTW

You can remove the ceramic resistor in the cap, it’s only there for old style spark plugs with no resistors.






As mentioned earlier

Get to TDC and check everything lines up, unlikely to be the issue as it runs.

[charliext1vj]

Barry, I would have done a more logical diagnosis route but what gets me is he says it works fine once started.
But without hearing it we cant be sure - if it was a fuel supply issue I think it would try and pop and bang on start.
My guess it is low on compression or duff inlet rubbers.
Interesting problem for us a pain for him!