feetupfun

The properties of different oils do make a difference to the issue of the plates not wanting to separate but the underlying cause is that the friction plate pads can act like suction cups against the steel plates. The proper fix is to roughen the finish of the steel plates to help break the vacuum and to remove any grooves in the basket fingers. Grooves there can hold the plates together when the clutch has load on it. For a temporary improvement, use the lowest viscosity oil that will also provide enough lubrication for the chain. If it was a racing motor, the primary chain would not enjoy it if you use ATF but for trials use, ATF is usually OK for lubrication and is very good at breaking the vacuum seal. There are also name brand low viscosity gearbox oils that will work well for this issue and questions like yours usually get lots of suggestions for which oil is the best. OSSA primary drive casings retain some of the old oil during an oil change so if you want to get rid of all the old oil, an easy way is to loosen off or remove the clutch cover to drain the remainder out.

Two thicknesses of that plastic coating and that washer being new would not be helping the situation

Fan running backwards. Air trapped somewhere in motor coolant space. Radiator coolant passages blocked. Radiator finning blocked. Blockage/restriction inside coolant hose. Coolant lost into gearbox through water pump shaft seal. Coolant blown out through overpressure valve by head gasket leak.

I'm not going to yell at you about learning to ride with rubbish brakes. I hate rubbish brakes. Great brakes make riding trials or avoiding your older ladies on the road so much easier. I am going to yell at you because you can make your brakes amazing without fitting bigger (heavier) hubs. Get the brake drum surface re-machined. Get modern high friction linings fitted to your brake shoes. Get those high friction linings ground or machined to match the drum ID. Enjoy your amazing drum brakes.

Corrosion inside the rims. Not usually visible from the outside but very common on this bike and if the spokes also need to be replaced, they are a very unusual Z design which can be a problem to find replacements for.

Post up a photo of what you have there

With the Alpina yokes, how do you go for mudguard and mudguard stay clearance to the exhaust and front downtube when the forks are fully compressed

Sounds normal to me

The offset is very different on those Alpina/Pursang yokes so you would need to change both top and bottom yokes. Using those Alpina/Pursang yokes increases the trail a lot so the steering feels very different. Some people like it that way some don't.

You will "progress" faster on the Beta but it sounds like you don't want to "progress" anyway. Alexyz is right in that a TY175 or Fantic twinshock is a totally capable bike for novice/clubperson level competition and if you get a standard motor TY175, it is even easier to ride for a novice than a Beta 200 due to the gentleness of the standard TY175 motor response.

I read it as the $800 includes the spokes, rim refurb labour and wheel build labour. That sounds like normal commercial rates to me and a good reason to do it yourself

Yes but they may be on the opposite of the world

It's your bike. Do with it what you will.

total

If it's a contest for reliability without performing maintenance, I would vote for the 4RT. If it's a contest for the bike that will let you ride in the most competitions, then I'd vote for whichever one has the best after-sales support where you live because riding in trials you are going to break things.

About 0.5mm side clearance cold for conrod to piston if the conrod is being held in position at its top end. If the conrod is being located from the bottom end, the side clearance at the conrod to piston connection can be greater

Most people fit preload spacers between the top end of the fork spring and the fork cap. They work by pre-loading the spring so that the neutral position of the forks in their travel is right while you are riding. The more of those preload spacers you put in the forks, the higher the bike rides at the front.

Those hat shaped caps are spacers for adjusting the fork spring preload. Springs come in different lengths and those spacers allow you to set the bike up to have the right suspension sag. If the bike was being ridden without them, you may not need to adjust the preload. If you are fitting new springs you will probably need to adjust the preload.

Neither of those are oversize markings so if that's all there is on the crown, then it is likely to be on the standard bore. The safest bet is to have whoever is going to rebore the cylinder measure the bore to advise what the minimum size piston kit is you should get.

I know I've got a spare TY250A lever that is undamaged but like I said, I'm further than Guy so the postage would be expensive. I just looked on eBay and there's one advertised for sale in the US for US$22. There's no way I would sell mine that cheap

I'm still here. What is it you are after?

https://www.yamahaty.com/english/ty125en/elec125en.html

Lorenzo answered about the sleeve gear type that has the sintered bronze bushes. Sounds like that's what you've got

Inspect the gearbox output shaft. It is a short shaft that will have either a pair of sintered bronze bushes or a pair of needle roller bearings inside where it runs on the main gearbox shaft. Both types can wear/fail and cause consequential damage to the gearbox gears due to misalignment (breaks teeth off). Wear in the sintered bush type is very common. Both the shaft surface and the bushes might be worn. I haven't seen a needle roller type fail but it would probably be more spectacular. Check that the kickstart return stop is not bent or burred and has a nice action. This is a fairly common failure point. Also there is supposed to be an aluminium washer on the end of the kickstart shaft. This may be worn out or missing.

https://newellmotorcycles.com.au/pages/bultaco-history your frame is a model 150 and your motor is a model 80. Open the link and you will find the years for your frame and motor