dan williams

And possibly explosive?

Manufacturers saving pennies basically. Good designs implemented by bean counters is how most products go wrong. They work good enough to get out the door but are never fine tuned enough to be perfect. What's fascinating to me is the various reactions from owners some saying just get on with it and ride the thing to those like me who will have custom parts made and spend hours twiddling to make it perfect.

Any Mikuni VM series parts should fit.

Er, welcome to the forum?

The Mikuni is quite a good carb when tuned and you may be confusing some things here. The classical definition of flooding an engine comes from the days of carburetors in cars that had accelerator pumps. If the engine wasn't running and you pumped the throttle too many times the intake manifold was full of fuel often fouling plugs with gas. These carbs don't have accelerator pumps so that can't happen. The problems commonly ascribed to the Mikuni is a condition where fuel gets splashed up into the vent tubes for the float bowl and then continues to flow because the vent tubes are too long and end below the float bowl causing them to act like siphons. The vent tubes are the two hoses that come out of the sides of the carb. The other hose that comes out of the bottom of the carb is the overflow for the float bowl. If fuel is pouring out of the overflow your float valve is malfunctioning. This could be an assembly issue, floats rubbing on gasket, adjustment way off or a worn /damaged float valve. First off remove the carb and nip a small hole in both of the vent tubes about halfway up the carb body. This kills the siphon action and any fuel that gets splashed up into the tube will just flow out the tube or flow back into the float bowl. While you have the carb off open the float bowl and make sure the floats are not rubbing on the float bowl gasket. If the show and wear marks trim the gasket with an X-Acto or similar razor knife. Make sure there is no gas in the floats as they can spring leaks and hold the valve open. Check adjustment for float height and travel (that little tab that's bent at a 90 degree angle and hits the tower the float pivot pin goes in). The valve only needs to open a few mm. More than that and you won't get anymore fuel flow but the floats will slam around causing the mixture to be inconsistent over rough terrain. This tab is usually set to allow far too much float travel. Check the Viton tipped needle for debris or damage and same for the brass valve seat. Big advantage of the Mikuni is the replaceable valve assembly. The Keihin is just machined into the body. All the instructions for soldering tubes and drilling extra vent holes is overkill. Nipping the holes in the tubes works. As for starting issues that generation of Betas was infamous for the ignition trigger coil going bad. It's easy to think the problem is caused by the dribbly carb but it was often not the root cause. ...and I hate Del'Ortos

And on a slightly geekier note I think I realized why the cam profile looks familiar. It’s a sine wave wrapped around a curve. I think only Jon will appreciate that detail. The rest of you just think I got too much time on my hands.

Ooooo more experimental parts are in.

I think there’s still some hydraulic lock that makes the bike jump a bit when the clutch is cold and hasn’t been actuated for a while but it’s still a lot better than the drag across the parking lot you get from the glue. The four strokes seem to have less consistant results and that may be due to using six of the thicker fiber plates.

Lay it on it’s side. Remove shift lever. Take off the four allen head screws on the clutch cover. Remove clutch cover being careful not to damage o-ring. Undo six bolts holding clutch pack in. DO NOT PULL THE CLUTCH LEVER AFTER REMOVING THE BOLTS!!! Don’t touch it or you can pop the piston out of the slave cylinder and a simple job will become a real pain. Remove springs and washers. Remove pressure plate, bearing usually comes with it. Remove clutch plates. I find the best tools for this are dental picks. They allow you to reach under the plates and pull them out individually. At this point you can reinstall the o-ring and clutch cover if you don’t want to leave the bike open on its side. Don’t touch that lever though. I’m warning you!!! Now dress the plates removing glue and polishing the tabs per the clutch fix instructions. Reverse the process to reassemble the clutch pack. Once the plates are back in and the pressure plate and bolts/washers are back in you can pull the lever with the bike still on it’s side to see the pressure plate move. Put the cover and shifter back on and go ride. Piece of cake except for the mind numbing effort of cleaning the plates.

Grab the clutch lever and open the bleeder on the engine case. If fluid comes out and the lever compresses the master cylinder and hose are good and you have a mechanical problem in the clutch assembly/slave cylinder. This is usually a problem caused by incorrect assembly of the clutch and/or actuation mechanism. http://www.sherco.com/tl_files/core/pdf/spare_parts/WEB-Spare_parts_FACTORY_2016.pdf

This should be sufficient. Spacer clutch order 05-18-2015.pdf

That would be my guess. Of course without a schematic I could be wrong but it seems the only way the thing could work if you are correct about the other connectors.

I believe the yellow wire is the ac feed from the stator. I assume the ground lug is the other side of the ac feed so it needs to be bolted to the frame.

“I don’t get it Luigi, We never have enough of these cam follower arms!” Luigi, who assembles the kick stands, quietly snickers.

Anything look familiar?

So while I’m waiting for parts to experiment with I wanted to tighten the kick stand which is, as always, loose. So I take it off to have a look and.....

Looking at the press release for the RR125 lots of interesting stuff jumps out like integrated clutch MC in the side cover. Ability to add electric start to the engine. Different metodology for making the gears. Some of this could carry over to the trials bikes. It’ll be interesting to see if they want to compete with the Contact ES.

Let the prototyping begin. Rendering of the cam arms I'm having made. I'll fit this with 11mm bearings instead of the 16mm bearings. What could go wrong? I love emachineshop. I can design a part and see it made real in a few weeks without breaking the bank.

Eric, do you want the measurements or where to get a set. I'm a little confused by the question.

There aren’t enough prizes to go around because we’ve all done it. Multiple times. In the same day.

What typically happens is an accessary manufacturer checks fit over a range of years and then never updates their catalog with newer years even though nothing has changed. As said above check the numbers from the Beta parts lists and if they match the accessories will fit. For example if a Jitsie part says it fits 2009 to 2016 and you have a 2017 look at the Beta parts lists for a 2015 and a 2017 and if the OEM Beta parts have the same number the Jitsie part should fit. Transitive equality If A=B and B=C then A=C

Well I got my spare parts to experiment with and already have some interesting observations. First is the finish on the cam follower arm is lousy. It's merely stamped out and not de-burred at all. This could lead to the follower not, er, following if it gets stuck on its burrs. Second, I think Beta used too large a bearing. The picture shows that not only is the bearing not seating all the way in the cam notch but there are two contact points which is not correct as they will try to move the bearing in different directions on the initial movement of the shifter causing wear on the cam. The other thing that is obvious is the shifter action starts ~2/3 of the way up the cam. My suspicion is that the design is correct and somebody got a good deal on 16mm bearings so that's what they used figuring it was close enough. I have to think about this a bit more, contact angle and slope/force calculations but I think this is easily improved.

It’s probably time to update the original document with the 24 pages of community learning contained in this thread. Something to do after my club’s trials this weekend.

Removing springs is what I used to do but then I’m an old guy riding bunny sections. Some of our more talented friends found that removing springs led to clutch slippage so it isn’t a panacea. I had spacers made according to a design by forum member IKB which do something similar without leaving parts out. PM me for details.

Quality of spark and its location can be an issue with an 01. You may be well served by just ripping the stator out and sending it to have its trigger coil checked/rewound. As in it’s either gone, going or going to go bad.