05 yz 250f wont atart

[kiel1111]

first off thanks for any input you may have i have a 05 yz250f that i just had tom morgen do a port and Polish also a 262 big bore kit he sent it back i had a mechanic put it all back together and then he had to leave it is really hard to start sometimes it will start first kick sometimes the 30th no rime or reason sometimes with the hot start it will start sometimes with the choke i rechecked the timing and its getting spark and when i twist the throttle with the carb off it squirts gas so heres what i have 188 main 72 starter jet 45 pilot running a honda needle ncyr 4 down 262 big bore kit Port and polish a yosh full system and 50% u4 and 50 % pump and a boyeson fuel pump ? y also bike seems to run mint when its warm

[motovator]

I have the same bike with an RPM 276cc big bore kit in it. I'm @1000ft above sea level, temps generating problems are around 60-65 degrees F.

Bike runs well once it starts, but then your too worn out to ride it@!

I have the JD jetting kit. I've tried the blue needle at clip 5 (too rich) with a 185 main and a 182 main, tried the red needle at clip 5 (too lean, but starts great! no choke, just kick 1-3 times; thing pops like crazy when you let off though and it runs HOT!), tried stock needle at clip 4 with 185 main, too lean and bike won't start, going to try stock needle at clip 5 with 185 main. Any warmer, and the 182 main will be just fine, but it's jetting for the cold weather were having now (20-50F).

JD jetting needle tends to be too rich down low for a big bore. I liked it before the big bore, but after, it just doesn't seem to work.

I let you know what I find. In general, for a big bore, you need to lean out the jetting. It's counter-intuitive, but the Vernouli effect causes more gas to get sucked in the same size venturi, even more than is needed for the increase in volumn of the cylinder.