Could be but 150 on top is a bit rich. I think stock was a 145 but I'm not sure. If you're new to trials bikes any sustained high speed work tends to purge the residual oil that puddles in the bottom of the crank. That's why you'll see the big boys rev out their bikes before a big up. Also why you'll find a lot of smokey bikes at a section after a long fast trail. Try dropping a size on the main jet and see if it helps.

Dan, I've deceided to take my engine out this weekend to see if the seals could be leaking, the more I think about it the more I think it is gear oil going through the exhaust as I never smell the strawberry smelling putoline 2 stroke oil that I use. Even the way the revs take a while to fall is pointing to the seals pulling air or oil through them plus the plug is always black and oily.

Andy.

Well I'm glad I deceided to strip the engine as I found a pair of very worn main bearings with one of thems ball retainer broken up allowing one of the balls to move around the race.

Glad to hear you found the problem!

Excellent news Andy. Good work. Will be surpassed by the news it's all back together and running proper.

Thanks, I hope it solves all my problems too! One question though when putting the gears and the slotted barrel that the selector forks run in is there a specific position for the forks to be in or does it not matter? I have slipped the gear lever on to the shaft and it will select gears but not that easily as I still need to put the clutch outer casing on and can't borrow the impact driver until the morning.

When ever you split a motor. Nuetral is the desired position.

I've got nothing for you on this except gears always seem harder to shift when the motor's on the bench and you're doing it by hand. To be honest Beta's are notchy shifters anyway.

Hi Starr870

Tell me to butt out if required, but I don't see the connection between worn crank bearings and your original concern (bike not revving out cleanly). Did you resolve that issue?

worldtrialchamp

Worn bearings pretty much means damaged seals. Two things happen with worn crank seals, air leaks into the crankcase during the negative pressure phase causing a lean mixture that is dependent on RPM and loading. Impossible to compensate for with jetting. This also reduces crankcase pressure causing a loss of power at higher RPM where cranking pressure should be highest.The other effect is transmission oil leaking into the bottom end further weirding out the mixture. I think once he gets it back together, hopefully with a set of rings (why the hell not?) the bike will run like the proper beast it is.

Hi Starr870

Tell me to butt out if required, but I don't see the connection between worn crank bearings and your original concern (bike not revving out cleanly). Did you resolve that issue?

worldtrialchamp

Being the bearing race was broke, the engine ran out of rpm`s due to the drag and damage. Besides the crank bouncing up and down.

Good news it lives! Started it tonight and it runs so much quieter and the revs drop straight away when letting the throttle off, it was getting a bit late so I couldn't do a full test but things are looking up. I will have a good look at it on Friday as I have a day off.

Awesome. Now go out there and ride the beastie.

Cheers Dan,

I'm riding in my club championship tomorrow so will see how it goes, I have put the needle back to the centre groove as a start to see how it runs but I will check the plug throughout the day to see how the mixture is, i'll let you know.

Andy.

I rode last sunday and the bike is so much better, no clouds of smoke and its reving properly in the upper rev range. I treated myself this week after the satisfaction of completing all the engine work myself and saving on all the labour that the shops charge by buying a set of Boyeson reeds and a jetting kit from "Trials and Tribulations", hopefully this will be the icing on the cake to my engine tuning extravaganza!!!

Andy.