feetupfun

Have you tried using the bearing dimensions to find the bearing ID for the second bearing, using the same pattern as the other bearing. It is likely to be another Koyo bearing. The first bearing number 20NQ3212 comes from: 20mm ID, NQ = type of bearing, 32mm OD, 12mm wide

I remember someone posting their local rules up years ago and there was a rule that really got my imagination working: "The rear wheel exits the section before the front wheel" (scores a 5)

The in-line axle 35mm Pursang forks I inspected today have taper-top fork tubes which means they are from a Pursang that was made before they went to a clamp-type top triple clamp design which happened around 1972 from memory. The Pursang sliders are the same internally as leading-axle Alpina/Sherpa T/Matador fork sliders of the same era.

Sounds like something is wrong. I've fitted lots of tapered steer bearings to TYs and the nut has always screwed down to the same position on the stem as it did with the original bearings. A photo would be good

It depends on what you are seeking to be able to say if is the ultimate set-up or not. With the square barrel, it would no longer look like an M49. If that doesn't matter to you then it sounds like a fun experiment. If you haven't seen many Sherpa Ts with reed valves, maybe you are looking in the wrong place. In some parts of the world it is a popular mod on late model Sherpa Ts, but not on early models like the M49. I suspect that the reason for this is that if someone wants a competitive Sherpa T, they start with a late model rather than an M49 due to the superior chassis dynamics. If people want to enjoy the awesome look of an M49, they would probably not want to make it look unusual/hybrid/ambiguous which would happen with a square cylinder or a reed valve. It's fairly rare to see reed-valved Alpinas probably because the main benefit for the Sherpa T motor is improvement in smoothness and even running of the power, which is not an important issue with Alpinas.

Whistles can be helpful as long as the sections are far enough apart so that the riders can't accidentally hear a whistle from another section. Sign language can be helpful too - holding your hand open to indicate a 5 so if the rider is in any doubt, they can look at you

Have a close look at the hole in the needle jet. It should be round, but they wear oblong. That jet and the needle that rubs on it (the slide needle) wear very quickly and cause the symptoms you are describing, hence why people are telling you to buy a proper carburettor

I bought 35mm Pursang sliders for a similar reason but haven't got to doing it yet. I can assemble a leg to make sure in a few days time if it helps

What sort of info? It's a popular and well-regarded model Some people have the brake pedal on the left side to get a better feel

Well my memory was wrong about the M198 engine being apart. I found the motor re-assembled and mounted in the frame!!! I did however measure up some 250cc pistons that had come out of M85, M85 and M49 engines and they were all different rear skirt lengths, and the rear skirts had all been shortened. I measured from the crowns to the edges of the inlet skirts and got 56mm, 58mm and 59mm. One of the M85 cylinders had had the top edge of exhaust port raised in one window but not the other window, so I know what you mean about being ruined by someone with a grinder (and is why I bought a second M85)

I do have a M198 (a 238cc Sherpa T contemporary to the M212 Alpina) and it came with the original piston, so I will dig that out and take a photo

Only the M99 (325cc) Alpina model barrel is the same as the M92. After the M99 model Alpina, the stroke was made longer to make them 350cc, so the later Alpina "350" barrels are also longer, so are not the same as the (325cc) M92 barrel

Bultacos of that era used the same basic piston but the induction side skirt was shortened on the models that were designed for top end performance (Pursang, Astro) to increase inlet port duration. Not having a reed valve meant that shortening the skirt was a compromise and took away from the performance at low RPM. Alpinas and Sherpa Ts that I have worked on mostly have had the full length inlet skirt but some have had pistons with shortened inlet skirts (and other porting changes) that were previous owners work. People do fiddle around with engines. The important thing is that the inlet skirt provides the correct inlet timing. If you want to be certain of the inlet timing, you can confirm the inlet timing with a protractor or "degrees wheel" against standard timing. I rode a Bultaco with similar port timing to the M212 (M49) for a couple of years before I pulled it apart and discovered that it had a shortened inlet skirt (about 4mm). After the rebore and now with an original type MAHLE piston that had the full length inlet skirt, there was an improvement in low RPM power, but it would have also had improved ring sealing as well as the more conservative inlet timing.

US ebay usually has lots of those primary drive covers advertised. The original cover on a M92 is the most commonly available type of cover and sometimes called the boot heel shape. A good M92 cylinder will be much harder to find because it is a wearing part and unique to only a few models This is the first boot heel primary drive cover I saw when I searched on US eBay https://www.ebay.com.au/itm/BULTACO-RIGHT-SIDE-COVER-FROM-1971-ALPINA-125-DIRT-BIKE-TRIALS-BIKE-ENDURO/123068514902?hash=item1ca7748256:g:HNcAAOSwuIRamwb I'm sure there will be lots more listings

Replacement primary drive covers are readily available

https://www.ebay.com.au/itm/Ty175-Yamaha-Trials-bike-gearbox-gear-set/323173172248?hash=item4b3e9f4418:g:oMYAAOSwu4haukF4 TY175 gearbox in Australia. There was one in the US too just now when I looked

I see a lot of TY twinshock parts being advertised on eBay by wreckers in the US. There was a gearbox listed the other day, not sure if TY250 or TY175

Sorry, bikes are assembled

Maybe you accidentally did it as a preview

Yes your single seat looks to be in the normal position. The seat pad does shrink over time which makes that gap slightly bigger than the brochure photo. I assume you have tried buffing compound to get rid of the stain from the long seat touching the tank? My original TY250A model tank has some stains in that light colour area that I haven't been able to buff out, but I'm happy to just leave it alone. The world is full of repainted TY250A fuel tanks but there are not very many TY250As that have the original paint that still look as good overall as yours. I love the look of my original tank so much that when I ride the bike in trials, I fit a repainted tank, to avoid the risk of damaging the original tank. It's good that you have fitted suitable gearing. Riding at a steady 45 MPH should not cause problems with engine heat because 45 MPH is below the speed where air drag ramps up dramatically, but if you were wanting to go for a brief blat along a freeway (maybe 30-60 seconds at 60 MPH), a B8ES would be more suitable and if you were going to run it at constant high speed for more than a minute, a B9ES would be more suitable. The middle electrode on a spark plug has an ideal temperature. Too cold and it will collect deposits which conduct electricity and too hot and it will lose metal quickly. The length of the metal part of the centre electrode determines how fast heat is conducted away from the tip. If you look in there you will see that there are different lengths for different plug numbers. If a plug tip is getting too hot, it not only disappears quickly, but also radiates heat which can overheat the crown of the piston. It's always safer to run a colder plug than a hotter plug for this reason. Before you fit a B8ES, go for what is a normal ride for you with the B7ES and then when it cools off a bit, take the plug out and have a look at the middle electrode. Then fit the B8ES and go for a similar ride and then inspect the centre electrode and you will probably see that the deposit on it is a slightly different colour. Fuels are different throughout the world and other bikes have different jetting and are ridden differently which means there is not much point looking at photos of other people's sparkplugs but there are generalisations you can use to know of everything is fine on your bike. Because you have told us the oil type, mix ratio and plug number you are using and that you ride it mostly on the road, I can say that your plug tip and the ceramic insulation around it should look totally dry and with a colour in the range from mid brown to light grey. When you fit the B8ES and do the same test, the colour will probably be a bit darker. Bear in mind that the plug tip colour shows the recent history of what was happening inside the motor so if you are interested in plug colour from riding at 45 MPH, do the inspection somewhere very close to the riding and don't let it idle for long. For gentle road riding an air-cooled bike with correct air-fuel ratio, 50:1 synthetic oil is fine. You can re-use the head gasket by annealing it. Usually 14 PSI on a TY is enough to avoid having a tyre overheat or cause squirming on a road ride. The higher you go above that sort of pressure, the worse the ride on bumps. As for those paint chips, you can probably find some nail polish to match the colour. Nail polish is chemically compatible with the paint on the tank and it's also good fun taking a fuel tank to a cosmetics counter.

Can you see why it is leaking? Is the vent hole clear? Has the blanking plug come loose/been knocked out of position? An option to JB weld is to fit a new blanking plug or refit that one using sealant

I would think you could pick up one of those brake plates from a wrecker fairly easily. If you are stuck post up the important dimensions and I'll have a look to see if I've got one spare (axle diameter, drum diameter and a photo showing the outside)

Plenty of montesacotaphiles in Australia Daniel

I don't think that a carby like the standard TY175 carby is available new from Mikuni. I think they do a 22mm carby but it is flange mount so you would need to machine off the flange and fit an inlet spigot.

You can buy that clip from bearing shops