I've got a 2000 xplorer 400. I blew a hole in my crankcase awhile back and replaced the crankcase. I replaced everything, gaskets, bearings, seals, everything. It's been back together and i have been fighting with it for a couple weeks. Here's the problem, it starts but cuts out bad in the low range. I figured maybe it was my carb so i took off my 39 kehihn pwk and switched back to the stock 34mm mikuni. It did the exact same thing. I have changed the jets and it seemed to run better with a 230 main jet than anything else. I tried switching the pilot from a 35 to a 38 and nothing. I moved the clip on the needle and nothing. I put a brand new throttle and choke cable on it and no difference. I removed the belt drive just to look at the crank turning and nothing was wrong. Everything is timed and aligned perfectly. What could be causing this problem? It has a wiseco .20 over piston, port and polish cylinder, head milled .010, hpd exhaust, k&n filter, and boyeson carbon fiber reeds. I have checked everything and can't figure out what the problem is. Any help is appreciated.

 

I have an explorer too and mine cut out also. I'm not sure this will help you but it's worth a shot. Take the plug wire loose from the plug and try twisting the boot around the plug wire. The boot has a small threaded type bolt in it that the plug wire threads onto. therefore if it is loose you won't get the right spark. I've had several different kinds of atv's in the past several years and this usually happens due to vibration. Sometimes if you make a mod you may also loosen it up or even changing a plug. I spent about $400.00 on my polaris and they never did get it right. Finally one day i went to change the plug one more time to see if this helped and the plug wire boot just fell off in my hand. Post a message back if this helps. HAPPY FAST TRAILS

 

Thanks for help. I believe that you solved my problem. I got home and just barely pulled on the wire and the boot came right off like it wasn't connected. I am going to buy a new spark plug boot today. I believe that will fix it. It would explain why it was running the way it was almost like it was out of time or something. I will post back to let you know if that is in fact the problem. Thanks for the help again.