1991 XT600EB Issues
 

I have a Edge Sidewinder that has a XT600E engine it it. I bought it as a semi finished project and have been rectifying all the issues with it (which has been extensive)but have got a couple that I haven't as yet. I thought this may be a good forum who may be able to give me some pointers.

Main issue - starts up easily, runs well for a short period till it warms up then starts making metallic noises, run rough then stops. If I try to re start it backfires. If I let it cool down for 10 minutes it will then start fine again.

Things to note -
I've rebuilt the carby's and upsized the main jet 5 points. I tried installing a larger idle jet but the motor ran rough. When I reinstalled the stock idle jet it ran fine. Secondary jet is stock
Tank is on side of buggy so it uses a fuel pump. I've installed a fuel pressure regular now as I thought this to be the problem. Set to 1 psi. No dice.
I've fiddled with the float level. No dice.
I've tried changing spark plugs. No dice.
I've changed the oil and filter. Oil seeps from bleed screw if loosened so appears to have oil pressure
I've installed a new set of headers and seals
It has a unifilter setup
It has a straight through style muffler

The metallic noise is the worry. Why does this start after warming up?

Are you 100% sure that all the carb jets/airways are clear?.. why did you change the jetting?..have you considered putting the carbs back to stock?..air/mixture screw set correctly?..tappets adjusted correctly?...

Check for spark when it shuts down hot , stator or pickup coil maybe failing hot. Also verify there is fuel in the carb bowl as soon as it shuts down , that will tell you if its a fuel supply issue , most other carb issues would have other symptoms even when cold or slowly get bad , not just shut down.

Also check compression , possible the cylinder is bored too small and the piston heats up and starts to get stuck , would show up by now as poor compression.

Compression etc
 

So I've tried a few things over the weekend. I'm looking to try everything prior to pulling the motor down. So here's what I tried.

1) Checked the valve clearances - This turned out to be a drama as the motor is jammed up to the side of the buggy. I had to use a holesaw to cut through the side panel next to the motor to provide a view panel to the timing mark. To do that I had to remove the seat. to remove the seat I had to remove the floor of the buggy. Anyway when I checked them the clearances were way to large. I though perhaps this was the root of the problem. I adjusted the valves then ran the motor. Bugger. Still the same
2) Connected a gravity fuel tank - just to ensure it wasn't a fuel pressure issue I connected a gravity tank and ran the motor. Bugger. No change.
3) Checked Compression - Compression reading was 185psi which is above the maximum. The manual states this may be due to "coking" of the piston and valves. Could this be the issue? Note it does backfire when you try and restart hot.
4) While the valve covers were off I had a look at the Cam to see if there was scoring. None evident. The cam looks in very good condition.

The other issue the buggy does have is its not charging. I believe the stator to be at fault. As I have a spare I'm going to change it. It'll be the same problem as accessing the timing mark. I'll have to pull the motor out. I had been wondering if the pickup was also faulty thus affecting the timing. The metallic noise does come from the exhaust. The tappets and cam are quiet when running.

Carb Mixture
 

It appears I may have gotten to the root of the issue. I had bought a kit to upspec the carbs from the US (Sigma) as there was hesitation when revving the engine. This was with everything including the mixture set at factory setting. I had put this down to the fact I had little back pressure due to the exhaust and a Unifilter being used as the Air Filter. When reading through blogs on the matter it is recommended to install larger jets etc after modifying exhausts and intakes. As part of this I raised the needles one notch on each carb. What I've found is that in doing that the idle mixture screw wasn't functional and you could screw in completely and the motor would still run. I used a Gunson mixture tool and even screwing in to the stop the mixture was still rich. I've put the needles back to the stock location and now the mixture screw is functional. The engine now warms up and doesn't cut out. Its not perfect however with more to do

Did you check/clean the float needle filter?

http://www.partsnmore.com/images/parts/480/48-1572.jpg

Mezo.

Carby
 

Thanks Mezo,
Yes I actually replaced it when I initially serviced the Carb

Cheers