konrad

Although jetting has an effect on rate of combustion, that's not what causes kickbacks. When a kickback occurs, the force from combustion pressure exceeded the force from flywheel inertia. Basically, the combustion pressure was high enough (too much burning too early) before TDC (rather than after TDC) to cause the piston to turn the crank backwards. Ignition timing for starting is retarded from normal running for this reason. It's possible the stator plate is too far advanced. Or it's possible the ignition system is intermittently behaving badly. Do you have a timing light, a helper, and a dark place to work? If so, you can see it the ignition timing is different from normal when a kickback occurs.

The trials bike looks heavy. Although I am heartened to see a gear-change lever. I feel having a gearbox is the way forward for electric trials bikes. I have mixed feelings about the conventional clutch. I liked it on my 4RT as it was zero-maintenance and had a fine feel. But a small diaphragm clutch is much lighter. To me, the motocross bike looks better suited to its intended purpose. And, like the Stark Varg, the MX bike has no gearbox.

I knew I had seen something like that before, and kept thinking antique board-track racer (which was not right). You can clearly see from the photo it's just a cut-and-welded standard bar -- not even a custom bend.

I downloaded a large version of the JPG. You can clearly see a gear-change lever!

When a DC motor starts, it draws several times its normal running current for a fraction of a second. What's worse, frequent starts or constant running? Depends on the duty-cycle I suppose. Either way, I would not lose sleep over it. The thing that kills fan motors is hitting them with a blast from a pressure washer. If only there were some type of automatic control to turn the fan on and off... 😛

It depends a lot on the ambient temperature and the condition of the cooling system. I would not worry about wearing out the fan motor. A more important issue is over-cooling the engine. Generally, competition 2Ts are run as cold as possible to improve charge density and maximize horsepower. But trials bikes rarely need maximum power. A more important consideration is improved charge vaporization (best throttle response) and a warmer intake charge helps that.

You should perform a pressure/vacuum test. There are many instructional videos on the topic on YouTube. This is the shortest and will show you the basic concepts: https://www.youtube.com/watch?v=kUmeyVcnZrs

I agree with lineway. Have you examined where the idle screw contacts the slide? Wear on the slide will cause difficulty setting the idle speed. But brass slides are less susceptible to that trouble than aluminum slides.

It's easy to try the encoder re-calibration process described here: https://www.electricmotiontech.com/home/em-epure-race/motor#h.aqwdzouw61q4 It's possible the throttle signal is out of range. You can try unplugging the throttle, cycling the battery on/off and then reconnecting the throttle. A crash can also pull on the handlebar wiring and cause trouble. It's best to have some slack in the wiring to the handlebars. Check for poor contact at all the connectors. Failing that, it will take someone with electronics knowledge and a multimeter.

You need to explain the problem in more detail. Do you have the optional regen lever (EM calls it PRB-R)? Are any tones emitted by the motor when you press the map button? Note that the controller will not permit the motor to run if there is a fault with the throttle. You can find the wiring diagram here: https://www.electricmotiontech.com/home/em-epure-race/wiring-diagram

There is a saying in electronics troubleshooting, "If you can't make it better, try making it worse. You may learn something." Based on your measurements, the finger height is nearly a millimeter out of spec. I would correct that. I have found it difficult to measure the clutch pack thickness accurately. A caliper is better than a micrometer for this job due to the increased surface area. The variation in pack thickness is important on the OSSA. Here is the procedure to check that: https://www.ossa-efi.com/home/my-upgrades/clutch-control-ring#h.twzu1hiimf5e The two good rides is a puzzler. Did you soak the new friction plates in oil overnight prior to installation? I find that helps maintain consistent operation. Finally, it's not something crazy like inadvertently mixing DOT fluid and mineral oil in the clutch hydraulic system is it?

Good question. It would not with a wire-wound spring. But disc springs are not like wire-wound springs. The finger height being wrong could also change the leverage ratio. Are you sure have everything assembled correctly? On the OSSA, the fingers have an inside surface and and outside surface. The difference is subtle but noticeable. You should be able to see which way there were installed originally by slight wear marks.

I don't see why you couldn't re-weld it. BUT... is the weld designed to be the weak link that fails thus preventing more costly damage elsewhere? I assume a crash on the gear-shift caused the weld to fail. Because OSSA gearboxes are so fragile, I machine a Nylon washer for the shift shaft that goes between the lever and the engine case. This prevents the shaft from being knocked inboard. No gearbox failures from crashing, but unsure if I have ever actually had occasion to test it.

Now you know it's out of tolerance. GG sells different thickness steel plates to correct that. Alternatively, some combination of new and used plates may bring it back into tolerance.

Some applicable information here: https://www.ossa-efi.com/home/engine/clutch#h.844fxvcen1dt