feetupfun

I would reuse that piston and if the ring end gap is still OK, reuse the rings. For the little end bearing, do a visual inspection on the rollers, the pin and inside the conrod hole with a magnifying glass. If it all looks OK, reuse them too. You will find that trials two strokes running modern oils gum up the rings at an alarming rate, especially if there is too much oil in the fuel.

Maybe they are good storage container for bike parts?

Yes the cable may have been damaged, making the return action (throttle being closed by the spring above the slide) sticky. Another common crash damage thing is the twistgrip tube being pushed against the end of the bars, also making the cable return sticky

My 348 is 195 mm centres

There is normally only a tiny clearance between the torque link and the pivot arm

Post up a photo if you want to know what's up

could also be cable damage

You could get the seller to measure. If you can say which design cover you want I can measure some up for reference

Do you mean a Yam-frame Majesty or a Godden?

Set the nuts so: The pressure plate moves out parallel. There is just enough drive to kick start the motor without the clutch slipping. You can set this with the clutch cover off but the plates need to be well lubed. Stainless steel lock wire. Copper wire work hardens. Of course it would go fine for a while without wiring but do you need the stress in your life of wondering if they were going to move?

Sounds like a tight time challenge. Good luck. Those mudguards look great. There's a few things that MK 1 MARs benefit from that you didn't mention. The standard ignition wiring comes out the bottom of the casing and typically gets squashed between the bashplate and the motor. There's an easy fix by rerouting it out the front of the engine casing. Only a problem if the bashplate touches things. The fibreglass bashplate will fall apart real fast if it touches things. That carby may annoy you enough to replace it with something different. If the bike is leaned over, it will flood. The rear axle bends very easily. A common fix is to extend the hub to the right with an extra bearing closer to the RH end of the axle. Kits for this were very common back in the day. The axle holes in the brake backing plates are not all on the same centre as the brake linings. Common fix is to enlarge the axle holes. To get it geared low enough for modern sections using a small enough front sprocket you will probably need to machine the sprocket nut to provide chain clearance. If you fit 360mm shocks with that set of sprockets, the chain will need careful attention to its adjustment to avoid sawing into the cross tube under the lower chain run.

The Scorpa 125 fourstroke with the Yamaha engine is a nice bike and incredibly reliable and long lasting. They are fine to ride but were seen as underpowered by many potential customers

Should be only one ball in total, but if there is three then it is probably just a work-around for the pressure plate being too far to the right

Yes not all threaded clutch hub spring studs are the same length and also yours may have had the original studs replaced. Also there is more than one length for spring buckets, but you said it was the studs hitting not the nuts hitting.

I don't think this is what you were describing but maybe it might jog someone's memory

You can buy them from Yamaha shops

Yes I give many ****s about geometry and have a strong interest in the geometry of 1970s trials bikes. They are great fun to experiment with. I make my own drawings because manufacturers specs are way too vague, sometimes wrong and usually refer to an unladen bike. Modern bikes have excellent geometry already and people fine tune it with the suspension, handlebars and footpegs.

I just remembered how much I liked that avatar

Could indicate air ingress and if so, most likely the magneto side crank seal. Could also indicate a sticky throttle cable or slide. In neutral the revs should go straight to idle RPM when the twistgrip is released.

The only difference I can see is that chappo's frame has sidecover mounts that look like M198/199/198A/199A while the photo from the book looks like it would suit something earlier.

Doesn't matter if it is a 348 or a 349, a 26, 27 or 28mm carby would be ideal. If you post up a photo of the carby someone will be able to ID it. Same for the bike and motor. The engine number is definitely a 348 and frame is likely to be a 349 but 349 frames change over time, hence the photo.

I have a few sets of Magical fork springs in use and love them but am having trouble trying to find where to buy more from since Yamaha-Majesty.com has been incorporated into In- Motion

There's nothing wrong with asking noob questions. Rear tubeless trials rims have a groove that the bead pops into like a tubeless car rim and tyre does. The beads are so tight in those grooves that you usually need to break the bead with a special tool or using a bench vice or similar. It's a very reliable design. The original rim on your bike will have a sealing band for the rim well. These are rubber and get hard with age and the rim surface can become rough from corrosion. If it leaks there you can always try a new sealing band or use a tube. If your wheel is holding air now and you don't disturb the sealing band while you have the tyre off, it will probably work fine with the new tyre. Yes good idea not to take the old tyre off till you have a new tyre ready to go on. If it was me and the old tyre is really old (they have manuf date on them) I would have a new sealing band and a nice lightweight tube on hand too.

I ride 1970s off-road bikes. I bought a Tubliss for using with tubeless rear trials tyres on tube type rims on trials bikes but when I weighed the Tubliss and found it was heavier than a tube, I continued with my normal method of trimming the beads on the tubeless tyres to fit the tube type rims. The $160 Tubliss is still sitting on my shelf Your Rev3 should have a tubeless type rear rim and if the rim sealing band is still sealing, it will work fine with a tubeless trials tyre without a tube or a Tubliss. Some people have problems with the sealing band not sealing against the rim and end up using a tube to avoid air loss. Once a tubeless tyre is seated on a tubeless type rim, it usually stays put but there was a problem a few years ago with IRC rears in this regard.

I bought the right size perforated steel tube for my 348 in the form of a go-kart muffler core and it was very economical. I didn't need to curve it though