feetupfun

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.

I couldn't hear any chirps. Maybe the high frequencies have been lost during the recording. Do you mean the farty noise when you close the throttle? (this is a normal thing)

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

It's quite normal for people to ride twinshock bikes in events that don't have a twinshock class

Every second-hand Bultaco I have ever bought has needed to have the crankshaft bearings replaced. They don't last long. There are a few other things inside the motor that may well also need attention. I suggest you use someone who has a good reputation for rebuilding Bultaco motors. There are design quirks that catch people out on their first Bultaco motor rebuild.

My 138 Alpina is the model that followed the 116 and it has a standard-bore 370 Pursang piston in it whatever diameter that is. I don't remember what stamping the cylinder had.

When fully assembled and with the motor stopped, the main gearbox shaft usually needs to be wiggled (by rocking the bike) to allow it to change gears. It looks like you have taken the clutch off. This usually allows the shaft (and the gears on it) to move axially out of their ideal positions, making gear changing harder. The clutch nut holds the shaft in the correct spot.

The benefit of the Rev 3 200 that we bought for my wife (who was a trials learner in the 2000s) is that the throttle response is gentler than the bigger Betas and it is easier to kick over to start than the bigger Betas. There's not much in it though. A 250 is fine for a beginner with a slow action throttle and if necessary the additional options are reduced compression, additional flywheel mass and retarding the ignition.

Yes and I wish I could buy it here. There is no Australian Importer

Jon I'm wondering if the "ELF Indoor Racing Fuel" (which we can get here) is as good as the Aspen (which we can't get here) for people's health because apparently that ELF fuel is designed to reduce the toxicity of the exhaust fumes when indoor racing karts and MX bikes.

Yes lead in petrol was a crazy idea but it was introduced in the 1920s because it was a cheap way to improve the octane rating. It was when leaded petrol was phased out in the 1970s and 80s that some engines developed premature valve seat recession and it was recognised that the lead had been a benefit to the valve seats.

Plenty of people have used a dishwashing machine for engine parts. A dishwasher will make the fins bright but only for a short while because they use a caustic solution which will dissolve some of the aluminium and leave it microscopically rough (open to rapid corrosion). Steam cleaning will not remove the existing oxide. Dry blast will remove the stains and oxide and will leave it microscopically rough (open to rapid corrosion). Vapour blast will clean the fins of oxide and stains and smooths the aluminium surface which greatly reduces the future rate of staining and corrosion.

I think you have described extreme lean fuel/air mixture with throttle slide at idle position. The "choke" is not a choke. It is a fuel circuit that provides a rich fuel/air mixture to help starting a cold motor. When the throttle slide is above the idle position, the starting circuit does not flow. That's why you can ride it around with the "choke" on but with the motor warmed up, it is too fuel/air rich when the throttle is in the idle position. There's a couple of things it could be. Most commonly due to blocked or restricted pilot circuit in the carby. Usually caused by the bike being stored with fuel left in the carby. Possibly due to air being sucked into the motor that is not going through the carby. Commonly due to leaking flywheel side crankshaft seal or at the rubber boot between the carby and the reed cage. Sometimes (very rarely) leaking cylinder base gasket.