feetupfun

Zinc-rich-primer (used for painting welds on galvanised structural steel) usually has a matt finish that is pretty much impossible to keep clean. I paint my frames with automotive lacquer for the same reason you mentioned - it is very easy to touch up the inevitable scratches, but it looks good, unlike the zinc spray paint

The 116 is the first 350cc Alpina model and it has a longer stroke than the 99 Alpina. The 99 may have been marketed as a 350 but is 325cc. Bultaco introduced "choice of shifting side" during the following series of Alpina (137/138). Some 137/138 are RH shift and some are LH/RH shift.

If you have the original rear rim on your 74 TY250, it will have a bead seat that is suitable to use with a tube and a modern tubeless competition trials tyre made by Michelin or IRC, or a modern tube type rear trials competition tyre made by IRC.

The only 325cc "350" Alpina was the very first "350" model and that is the M99 from 1972/73. All the "350" Alpina models that followed the M99 are 350cc (with the longer stroke). The M99 is the only "350" Alpina that shares frame and steering geometry with the Sherpa T of the same period. All Alpinas after the M99 "350" and M85 "250" share triple clamps with the Pursang/Frontera instead of the Sherpa T triple clamps. Some Alpina models also have a longer wheelbase than the Sherpa T of the same period, courtesy of a lengthened swingarm (M137, M138). Every model Alpina is a delight to ride. They all have light handling and incredibly good steering. The Alpina models after the M99/M85 have a bigger and much stronger front brake (shared with the Frontera).

I tried notoil but then went back to Silkolene because the notoil lost its stickiness after a couple of weeks. It is quite hot and dry here so it probably dried out faster than somewhere with a more temperate climate.

A stainless steel welsh plug does a good job for the oil pump hole

Sounds like you might have ridden something newer since then

The foam is "open cell" which means that what you see is actually like a skeleton of strands with random shaped pathways in between. The air flows around the strands in the skeleton because it is a gas. The dirt particles tend to travel in straight lines and will hit the skeleton at some point. To prevent dirt particles from working their way through through the foam, the foam skeleton needs to have a thin coating of oil on it all the way through so that the dirt particles will stick to it when they hit it. If you put too much oil in the foam, you will cause drag for the air by blocking some of the pathways (which will reduce the maximum power available from the motor) If you only put oil on the outside of the foam, then if any dirt particles which manage to get past the oily outside of the skeleton before hitting a strand will go through the foam and out the other side. Filter oil comes in spray cans and in bottles. Spray cans are probably a better idea because air filter oil has some light and fast-drying components that allow you to work the oil through the foam then evaporate off, leaving just the right degree of stickiness. Being a spray can, the contents are only exposed to the atmosphere after they come out the spray nozzle. When you buy filter oil in a bottle, each time the bottle is opened to get some oil out, some of those light and fast drying components evaporate from the oil in the bottle before you seal it back up again.

How long have you had it? Are you sure it is actually going into gear? My 348 requires a special technique to get it fully into first gear. If I don't do it, it goes back into neutral while I'm riding.

When I had the VM26 on it, I added a bush on the inlet bell to fit the standard Montesa connector to the airbox. With the OKO fitted it did not need a bush on the inlet bell, or stretching, to fit the standard airbox connector and it fits the connector to the cylinder which was from In Motion. If you are asking that question I'm wondering if you have read the info about fitting one to a 348 on the Mid Atlantic Trials website? My jetting is whatever it came with from Mid Atlantic Trials. I didn't pull it apart and haven't needed to pull it apart.

To answer your carby question, I've had a 26mm OKO on my 348 for a couple of years now and it works very well. Prior to that I had a VM26 Mikuni on it which was also good.

If it is a 360 Pursang cylinder then the cylinder will be longer than a 325 Sherpa T cylinder because 360 Pursang has a longer stroke. Yes the sleeve (and the barrel) could be machined shorter at the bottom to make the piston crown the right height for the cylinder, but the port timing will be wrong

Mine mount onto the frame exactly the same way as the standard peg mounts

If it helps, I had one of those diodes on my TY250D and it kicked back just as easily as my other TY250s that don't have diodes. I took the diode off the D motor for an experiment when I was diagnosing an ignition problem (that turned out to be a loose bullet connector on one end of the diode) and it still kicked back exactly the same. To improve your success rate when kicking it to start it, ease the piston up to as near to TDC as you can, either a bit before or a bit after, wherever it will stay still, but not too far before or past TDC. You are doing it slowly so it doesn't fire or go too far past TDC. Then let the kick lever return to the top and then give it the start kick. Keep full force on the kickstart lever as you move it, all the way till the lever hits the footpeg. That technique puts momentum into the crankshaft and flywheel before the piston gets to the firing position, so when it fires the motor will keep rotating forwards. People like me who have been riding these bikes for 45 years do that thing I described on autopilot, very quickly and don't even consciously think about it.

About your first question, no there was not a factory option to have Ty175 pegs further back. The kits to move them back and down a bit came much later and not from Yamaha. The TY250 did have a Yamaha kit that allowed people to have the pegs further forwards for trail riding

Some kits require the RH peg to be lifted to kickstart the motor. Some don't. I haven't seen anyone move the brake tip back to compensate the the peg being further back. The kit I've got doesn't move the pegs back far enough to make much difference and is quite a comfy reach to the brake pedal tip (size 11). The brake lever tip is adjustable fore and aft by reshaping the front end. It's a fairly common task to reshape it after hitting things with it. If you are still in doubt I will take some photos showing the distance with kit pegs

It can be fixed a few ways but what is the point unless you are going to stop riding it

Betas make a whirring noise even when everything is working perfectly because they have straight-cut primary drive gears. My 1976 KT250 also has straight cut primary gears and also makes that great sound. When your mains fail if there is any noise it is a rumble. Beta mains usually last for many years of normal trials use.

There is a reason why they leave the shields in. In the 1970s the Japanese two stroke trials engines had a ventilation system for the main bearings. There was a little port leading from the mouth of the crankcase to the space between the bearing and the crank seal (on both sides usually). Suzuki is an exception with their fancy CCI system on the drive side bearing. The Spanish trials bikes of the 1970s don't have that ventilation system. Guess which bikes the mains lasted for 40 years and which ones didn't last that long at all. Anyway, the bearing ventilation idea was ditched when brands like Sherco decided that a super-slim engine was worth sacrificing main bearing life for (the ventilation ports took up valuable space between the bearings and the seals). The first Shercos had a reputation for the main bearings lasting only a short time (one season) and this didn't go down well with owners so they tested the idea of leaving the bearing shields in place and found it gave a longer life to the mains. I'm fairly familiar with 1970s Bultaco motors (which have no main bearing ventilation) and from what I've seen when pulling them apart to replace the main bearings (which is every Bultaco I've ever owned), the bearings appear to have failed due to the balls and races having to continually squish little bits of carbon.

Leave the chain on and you can jam the wheel to hold the sprocket still to undo the nut

That screw has an offset pin on the end so you can adjust the angle of the clutch arm to offset for wear in the plates and mechanism. The offset pin lifts or lowers the clutch camshaft and the cam face is slanted to provide the adjustment

what is the history prior to the lack of spark?

Looks fabulous

You are welcome. I took a series of photos of three different cylinder types many years ago when I was helping someone work out which model cylinder they had on their TY250

Jeff what number is cast into the port side transfer port area