I have just bought a Beta Evo 250 2010 and the plug is very black and I suspect its running rich. Does anybody know what the air screw / fuel screw settings should be ? It's a Keihin carb so I need to know how many turns out the mixture screw should be.

Thanks

Phil

According to the User Manual (see http://www.betamotor.com/en/support/manuals) air screw should be 1.5 turns out from fully closed (closed is fully clockwise - so 1.5 turns from that position).

According to the User Manual (see http://www.betamotor.com/en/support/manuals) air screw should be 1.5 turns out from fully closed (closed is fully clockwise - so 1.5 turns from that position).

Thanks for that Peter, i've also saved the user manual for future referance so I can now get any info I need .Once again thanks

Phil

Jetted rich and/or too much oil in mixture and/or wrong plug heat range and/or leaky primary seal and/or retarded ignition.

Start with the obvious, does it run good? If so the jetting and ignition timing are probably OK.

Checking for correct plug is easy. Remember the plug doesn't have any effect on engine temp except when it is way too hot and can cause preignition. Other then that it's just like a thermometer.

Oil mixture is one of those mysteries of life. Some guys run 50:1 up to 100:1 I've found 100:1 with a good synthetic to be fine on my Rev3s but then I don't spend much if any time at high revs. I consider 80:1 to be conservative in a modern trials bike. Others will disagree.

Leaky primary seals or porous cases can let tranny fluid into the crank but this happens rarely.

Other oddities that can cause the plug to look too dark are plugged exhaust, sticking choke, a bad thermostat causing the fan to run constantly making the engine run too cool and high altitude operation where the bike runs too rich.

OK that's all I can come up with.

Jetted rich and/or too much oil in mixture and/or wrong plug heat range and/or leaky primary seal and/or retarded ignition.

Start with the obvious, does it run good? If so the jetting and ignition timing are probably OK.

Checking for correct plug is easy. Remember the plug doesn't have any effect on engine temp except when it is way too hot and can cause preignition. Other then that it's just like a thermometer.

Oil mixture is one of those mysteries of life. Some guys run 50:1 up to 100:1 I've found 100:1 with a good synthetic to be fine on my Rev3s but then I don't spend much if any time at high revs. I consider 80:1 to be conservative in a modern trials bike. Others will disagree.

Leaky primary seals or porous cases can let tranny fluid into the crank but this happens rarely.

Other oddities that can cause the plug to look too dark are plugged exhaust, sticking choke, a bad thermostat causing the fan to run constantly making the engine run too cool and high altitude operation where the bike runs too rich.

OK that's all I can come up with.

In answer to your questions, the bike starts fine and runs really well, it sounds crisp and responds to the throttle well. It has the correct spark plug in (new )and I have just changed the gearbox oil and nothing suspicious was found in the old oil to suggest any obvious problems.

Now we come to oil mixture. I am using PJ1 fully synthetic oil and mixing 65 cl per 5 litres of fuel.Now I don't know what that works out to as a percentage or what the quantity for 80:1 is, but maybe that is where my problem may be.

If somebody out there in cyber space could work out the correct quantities for me and advise I would be eternally grateful

Thanks in Anticipation

Phil

http://www.manxyouthtrials.com/two-stroke.pdf

http://www.manxyouthtrials.com/two-stroke.pdf

Thanks Dan thats brilliant

Phil

Also check your float height on the carb.

Also check your float height on the carb.

If the float height was wrong , wouldn't it flood out of the overflow when the engine wasn't running ?

Phil