I have been running my 300 pro @ 80:1 mix for quite a while and it runs fiine however it always seems smokey when going up hill. Sometimes ends up with the plug fouling also. Have tried screwing in the air mixture screw a bit to make it run a bit leaner. Anyone got any ideas, thought about maybe jetting up / down any thoughts / experiences with tuning for optimum performance from the 300 pro?

Have you altered any of the carb settings since new? Also the mixture screw should be 3 turns out in this weather.

If you aint changed the jetting from new its possible you would have had to wind the mixture screw out a fair way as they run weak on the standard main jet (Especially in winter), they need the next one up.

Also check the end of your HT lead as often the end of the lead gets burnt away and this results in a weak spark which leads to bad combustion and thus it will run a bit funny.

Good luck

Cheers.

Was planning another srip down anyway so will clean ou the exhaust and try a bit of tinkering. Thanks for the info.

I have had to replace a left side crankshaft seal that was leaking it was sucking trans fluid into crankcase

gasgas has a little passage where oil lubricates the left side crank bearing sometimes the seals got folded over in production also

good luck

hopefully just jetting but if it ran fine before crank seal would be suspect

Just a Basic check, you are running it on fully synthetic oil and Superunleaded petrol!? 75cc's (ml) oil to 5 litres petrol

Jools.

When you said that you replaced the left side crankcase seal, that is the seal behind the flywheel yeah? Did that mean you were losing oil from the crankcase? If the seal had rolled on installation would it not leak into the flywheel cover also?

Cheers.

no it didnt leak into flywheel it had two seals if I remember right one on each side of the crank bearing it was the inside seal that rolled over