Xr650l carb problem

[dikkobat]

Hi folks
first time poster here, grateful for ANY help or sensible suggestions.

i have a 1993 XR650l. Over the winter it has been stripped, repainted frame & engine, engine has been fitted with a new piston and ring, reassembled with new gaskets, it has a K&N and some aftermarket exhaust, not sure what kind though.

my problem is, that it starts easily enough, but when it gets to about 1/3 to 1/2half throttle opening, it starts to run eratically, like fuel starvation. I pulled the air filter tube off and you can see the slide oscillating up and down when it gets to these revs, and i dont mean just slight movement, its jumping right up and down. I have stripped and checked everything, blown through with an airline, checked the slide diaphragm and the air-shutoff valve diaphragm, everything is perfect, checked the choke, its fine, pilot mixture screw set to factor settings, but adjusted one whole turn either way but this does not stop the slide from jumping up and down. the slide has very littel resistance to it and initially i thought it was the diaphragm but it does not appear to be this that is at fault. Blowing into the diaphragm duct at the top of the airfilter side does cause the slide to lift.

its deffo nothing to do with coils/ignition/plug or valve timings. I had the carb off and there is only positive suction from the engine, no blowing back. valves have also been lapped in and are sealing perfectly.

If anybody ahs come accross similar or has ANY suggestions i would be most grateful, ive spent the last six days messing about with it and trying pretty much any and everything.

cheers guys!!

The Dikkobat

[Daz Max]

Have you checked the needle that runs through the centre of the slide?
(don't know the proper name for this!)
On my XR,there was a tiny amount of corosion which made the slide stick,then suddenly go,it may be that yours is slightly sticking?

[dikkobat]

yep, its spotless mate, i forgot to say that carb was vapourcleaned, but this shouldnt have made a difference as it is a non-abrasive process (and the slide/diaphragm was removed for this). The bike is looking great now, its just a shame it doesnt run worth a stuff

[kempouk]

have you tried flipping the choke off, some people forget that the choke setting is down for off and up for on.
on the 600'ds anyway.

[dikkobat]

Yep, good thinking, checked that. Im beginning to wonder if the valvetiming has slipped a tooth out or so? i had the carb stuck onto the hoover last night to simulate engine vacuum and the slide still does not rise when the butterfly is opened. And the diaphragm seems fine when visually inspected. bloody bike

[dikkobat]

Well, after much mucking about checking everything etc, i decided to open the engine and lo-and-behold......the valve timing was a tooth out!! it would seem that once you set the valvetiming and install the camchain tensioner, it effectively moves the timing out by one tooth. Set timing correctly and its up and running fine now, a bit rich on the jetting but will get that sorted this evening. And its getting the front end up in the first 3 gears so i am pretty happy.
A hard lesson learned but one i certainly wont forget. And i suppose on the upside, i got a nearly new carb off ebay for £20, so i have that for spares (was only that cheap cos the guy didnt know what it was off!).

Thanks to those that replied with advice, is always good to have a second opinion.

Cheers!

[Daz Max]

Christ, I'll have to check that.I've just fitted a new Cam on mine....