Problem with Kymco maxxer and KXR

[Leonw586]

Hi! Thanks for letting me join the forum, I came here to seek more knowledge in the ATV field, just got 2 Kymco's, a maxxer 300 and a KXR 250, for very cheap because they had problems...

The problem with the KXR 250, is that she starts and only runs for about 1 second and dies, I've been playing with the slide needle and the air mixture screw and I've been able to prolong the running time to 5 seconds at most and then she sputters, backfires a bit through carb and shuts off again, the carb has been cleaned thoroughly by me, as I've worked with keihin carbs before without issues.

Now, the problem with the Maxxer 300, is that she runs good for like 40 mins, then she begins to shut off at intermitent intervals, you can start her without problems after, but you can ride for 10, 20 or even 30 mins until she shuts down again.

For the Maxxer I've been thinking about a hotter plug maybe, but for the KXR I'm clueless, I'll swap carbs later to see how she goes.

Any help would be greatly appreciated...

[airshot]

I follow a routine in situations like these.  First, do a compression check, proper compression is required before anything else will work.  Check spark, a good blue spark that will jump a 2mm gap is needed, yellow means a weak spark.
If comp and spark are good, check fuel flow from tank, I have saw crud reduce or stop fuel flow, clean tank and hose if needed.  If all this is goog then get a quality rebuild kit for each carb, follow instructions to the letter, be sure all tuny passages are very clean, one spec of dirt can cause an engine to stop running. With good comp, good spark, good fuel flow and a nonrestricted carb, it will run, but you need them all to work right!!