[CP241]

Hello all, hopefully someone can help me narrow down or has experienced this before because i'm probably missing something stupid that is right in front of my face... I do have a lot of small engine experience.

Anyway... I'm a little stumped on this thing... sorry in advance for the long post, wanted to put as much info up front as i can.

I picked up a Yamaha G9 basket case for cheap. I've been wanting a gas cart for a while, just don't want to pay a fortune for one. Compression is perfect at ~170psi, no noises, smoke, or anything bad. Did not run, no spark. Wiring looked like the guy was hungry for spaghetti and happy to use a pair of cutters. basically completely trashed... brown wire to the regulator/rectifier was melted and wrapped around the airbox somehow... Step 1 was to strip the wiring harness and repair it. no problem there.

Anyway, no spark. Aside from the wiring mess, coil was obviously fried, ignitor was full of rust and corrosion and a brand new spark plug (wrong one for the cart). Bought a new regulator/rectifier, ignitor, and ignition coil. Lesson learned, don't buy the cheap ebay coil lol. after chasing my own tail with a *very* weak spark, picked up another coil at the local cart shop. Plugged it in, and immediately had a nice fat blue spark. Good to go, right? hooked everything back up, fired right up and ran great. I only ran it for 20-30 seconds but it ran. No idea how long the oil had been in there but it was black and nasty so didn't want to push my luck.

next day, change the oil, air up the tires and take it for a ride. This is where i'm stuck... it runs GREAT for the first 2-3 minutes. Then it becomes angry. It starts sputtering, backfiring through the carb, and loses any and all power and dies. If i take my foot off the gas for 10 seconds, hit it again it instantly fires up, will run great for about 10-20 feet, sputter, pop, and die again. IT will continue to do that until it sits for an hour or so. Then, lather, rinse, and repeat the cycle.

I've adjusted the valves (.004 intake and exh). It had a "mokini" carb on it (brand new) but luckily he left the original Mikuni carb in the front pocket. changed the fuel lines and filter, pulled the carb off and cleaned it out. a little trash in the bowl but nothing major. Put it back on, same thing. So I cleaned the Mikuni carb really well and put it on. No change at all.

When it dies, i've maintained pedal pressure, and confirmed spark is still big, fat, and blue so i'd rule out ignitor and coil (typical to fail when hot). No voltage drop at the coil or ignitor. Pickup coil reads about 560 ohms. Also, I've ruled out compression, still 170psi when it dies (checked compression right after it died). Pulling on the choke only kills it faster. I've also tried a shot of starting fluid when it fails and it doesn't even pretend to want to start so it's getting plenty of gas.

I can only come to the conclusion that it's running pig rich. Haven't been able to run it long enough for it to foul the plug or see anything there, but i've pretty much covered all the other bases. I've read about the airbox being picky and etc. but i don't think that's the issue because it runs great the first couple minutes, only does it after it warms up to operating temp. IT will also do it even if you're holding the pedal WOT. I can put it in neutral (shifter straight up) and manually hold the throttle wide open and doesn't make a difference there either. Also, removing the airbox completely (running an open carb) also does not make a difference, still same issue.

I'm open to any ideas you guru's may have