My KTM 640 LC4 is sputtering at all RPMs; it cuts out and kicks in again shortly after. I've tried everything and currently have the carb out for a full cleaning - but seems pretty spotless as of the last time I tried it. The problem started right after I gassed up but the fact that I messed with jetting too has diverted my trouble shooting focus. Right now, I'm 100% stock and running out of options. I'm wondering if I accidentally filled my tank with low 87 octane gas.
I hope, at the very least, you put in a new plug before all of this work.
The low octane fuel might make it spark knock but i REALLY doubt this is your problem, make sure the valves are in correct adjustment too. Little things will throw you, I always miss them.
I brought my carb to a pro, right away he said that I was missing the
small spacer that goes right above the main jet. It holds the needle
jet in, and must have fallen out when I was changing jets.
User error (or loser error) on my part.
Now I have to locate one. Unfortunately, there is no part number for
it listed in my schematic. Hopefully my dealer will have good
resources to find it.
Check H&H KTM www.ktmworld.com or call Letko Cycles I think is the name at 1-913-334-0881. They have both been around awhile and should be able to help if you have problems.
JW
My KTM LC4 does this too. It has 170 miles on it. I run 100 Octane low lead aviation fuel in it. Sputters,quits,restarts,confuses me. I have not messed with the jetting at all. I'm about to let the dealer have a go at it. I think the vent tube for the fuel tank is routed under the tank and might be partially pinched at times. I have not seen any debris upon draing the float bowl. Mine has done this only after an hours ride time.I would be interested to know what you find.