When first started my Gas Gas 250 pro 05 will not rev out fully it sort of labors, stutters when revving fully and when put in gear it stutters too. Though when up to temp it sorts itself out and seems alright ! I have been adjusting the mix screw, could this be the problem ? Many thanks for any reply's, Stuart.

check the rubber flap that suposed to stop muck entering the air box is not blocking the air intake. I had this happen and it wouldent rev out. I now zip tie the end to the frame next to the back break master cylinder, revs out cleanly now.

Check the choke system isn't leaking fuel past the stop. Has the inlet to the air box been covered. Is the air filter clean.

Ralphy

Why would you want to rev it out fully when it's first started/cold

Why would you want to rev it out fully when it's first started/cold

It's when i pull off at first, then when i give it some gas the bike stutters, and when you give it a bit more there's no response ! Could it be that i put too much Filter oil on the Filter ? I adjusted the Mix screw at the weekend to 1 and a half full turns out, i was told that that was the best position, the bike was running fine last week, so i may have been responsible for the problem myself ! I thought that if i asked someone might give me a few pointers.

Blocked air filter I'd change first. Make sure you squeeze all that excess oil off the filter.

Not sure if your bike is running the Dellorto, but seems most like the mix screw out another turn or so from that setting, all depends on your pilot jet number you see. And must be tuned and set to suit!

Although you really do need a bit of heat in the motor to find just how she runs, a tad lean off cold can produce a very smooth runner when up to normal operating temps it seems. My Sherco is no different running a #36 pilot jet.

It will fall on it's face off cold.