woody

Legally the plate should be full size, police are usually lenient for road use during a trial as they realise a full size plate will probably get damaged or broken off, However, it doesn't mean riders are immune from getting done during an event, it's at your own risk. By law an undersize plate is the same offence as not having one fitted. If you're using the bike for leisure and in built up areas it would be wise to fit a full size plate No to your GPS app, your bike must have a speedo fitted and in a place where you can see it

Speedo, doesn't have to be fork mounted or cable operated, you can use a bicycle one Horn, must be continuous tone so again, a bicycle one is fine. Bulb horn only on much older bikes Rear reflector - not needed. Unless you have functional lights then you should have one You need to be just as legal to push it with a dead engine as you are to ride it on a public road/area as you are still in charge of a vehicle,

The Haynes manual will be sufficient to work on the later engine, or the 5 speed manual sold by In Motion. The basic engine layout is the same and the values you mention will all apply. There are small differences between earlier/later engines such as the 199 engine has a shim on the clutch side of the layshaft which you won't see in the manual. The clutch springs are on threaded studs and tensioned by nuts, whereas the manual shows the earlier cup/pin arrangement. The 199 final drive pinion runs on needle rollers as opposed to bushes on the earlier engine When you reassemble be sure to test that you can select all gears with the gears and selectors assembled in the l/h casing. It's easy to get one of the selectors upside down as it will fit either way and if you do you can't select past 3rd gear. I think this is mentioned in the Haynes manual, not sure.

You'll never know the answer to how many rebores but the Dinamin pistons were common aftermarket pistons available for many makes of bike in the 70s to 90s, later called GPM, no longer available now. They were available in bigger sizes than the current aftermarket pistons for Bultacos

In Motion should have most of what you need https://www.inmotiontrials.com/

It's a 1975 250 MAR MK2, the engine and frame numbers are the same, just that the engine is prefixed M and the frame B. The frame number is on the headstock, maybe hidden by layers of paint as the original frame colour is silver/grey with white tank/sidepanels and green stripe. A previous owner has painted it all green and black engine/forks to look like the 1979 version

There is no point using caustic soda in the muffler of the front pipe as there is perforated tube in there with packing around it, the packing witll either have been blown out or be completely gummed up with old residue. If you're lucky it will be the former as it is far less messy to sort out. It has to be cut open, anything left of the packing needs to be removed, the perforated tube cleaned out, new packing added and weld back together. The same applies to the rear silncer, the lower part of which up to the top of the shock absorber is also packed

It seems that some of the first TR77 production run were produced with the same silver/grey frame colour as the MAR. I've not seen this documented anywhere but it's according to people who bought them new at the time who've said they came with the silver/grey frame with green tank and side panels. The more common frame colour was black. The mudguards were an opaque/white colour, no longer available I think, as opposed to solid white. It was the next model, the TR77 Verde that had the green frame and green guards It sounds as though you might have one of those that came with a silver frame, your frame number should start 63 so maybe it's an early number. According to Vitale Ossa the RAL code for the silver is 9006 - or the old 1970s Ford UK colour of Silver Fox is a good match

No holes in a 250 piston

Yes, normal for the 250

They could just be another, later variant of Betor damper rods, all the components are the same as the usual rods, just a different design but they function in the same way. If the forks work as they should there is no need to change them

The Ossa MAR had electronic but when they brought out the TR77 in 1977 (green tank bike) they fitted points to it. They went back to electronic on the TR80 Gripper. Either system will fit all of the trials models so maybe someone replace the elctronic on your bike with the points system, unless you have a TR77 rather than a MAR - engine number will tell you Can't help diagnose an electrical problem but you don't mention trying a different plug. Also possible is the pilot system being blocked or partially blocked in the carb

They're on ebay, however, getting them to sit flat on a curved surface without creases or ripples...... https://www.ebay.co.uk/itm/174995042817?_trkparms=amclksrc%3DITM%26aid%3D1110013%26algo%3DHOMESPLICE.SIMRXI%26ao%3D1%26asc%3D20210125103153%26meid%3Dc8849486c8574ffe98998953bf40daf3%26pid%3D100040%26rk%3D6%26rkt%3D24%26sd%3D174995042801%26itm%3D174995042817%26pmt%3D1%26noa%3D0%26pg%3D2046732%26algv%3DSIMRVIMLRV5WebV1_0&_trksid=p2046732.c100040.m2060&amdata=cksum%3A174995042817c8849486c8574ffe98998953bf40daf3|enc%3AAQAGAAAB8Ea37LkMCFnYSXAHlLtfgVdMp%2Fc6%2FvCY4PRvNQ45qGezsfD%2BSLr4efdblIya0XsZzjKs3%2FR17U21%2FPirmIzvuxeBlfyVuXGO5fPwow4P59GLNbSzyQOp%2BWUiNaHR8uxBfcjU0RdgxtAogbi2oxl2KiYgc0uPR1yvVgaLmmvPgki4DTC0mRU%2BSGODOKOyEXAn5nR9DRk0Uq4FaR%2FdMee4RaHvApGauJdkWOgNGk4UG47YG0ydTtA08SqlghgFsxg0wYLobezhrV9Zb%2FkgRqOeHyTzBrZ6kcbOZ91JYywD7Hpw9dYNtpbD9C9g%2BlIOq8%2FOGr9LVx92tYJzrObJmYLCmIkEC269EUjxZnEnTIdbE0kXpTXRaPZGjAlWyUGACSVBzs4EMUvd0s7CBqMHcZ914uU658eHnVsRarvW69JETaUGooyxozttvidgP15h5QbAnessqpFVeWN4GHQefRoimAumDEhzuoCPO3wS%2BDmh2pA0KJong6zzaG7g29sIzno8wm7ouRLS4h534vgZ%2BmZhPXqePfxCThVYpMKqceQJpVxj9H6OjPOPM7VnlEphqemj%2Fuad5qfcrqj3Uxc1LUZYHbR3zmKqUwV8mKbhlNlKamtd9YHlSjmNMpJw112as4cqOLrxMDlzG2j5DUa6zcQKDP8%3D|ampid%3APL_CLK|clp%3A2046732

You need to put a picture of the part you're referring to as from your description it could be a preload spacer or an oil deflector. Preload spacers are alloy and sit on top of the fork spring under the cap. The oil deflector is steel and pushes up into the bottom of the spring and sits over the top of the damper rod. I'd guess it's the deflector you're asking about Your damper rod is certainly different from any other Sherpa rod I've seen

I had a stator renovated many years ago by Bradford ignitions and it still works, can't remember cost as too long ago but not silly money. I recently had a coil break down and replaced it with one from In Motion which works fine

Wheel bearings just knock out from the inside with a drift but you need to dislodge the spacer tube in order to get a contact with the bearing inner race. If the tube is held tight between the bearings then and won't move then yes, it becomes difficult. Once out you can cut a slot into one or both ends of the spacer so that next time you can get at the innder race through the slot with a thin bar. Or, use a blind bearing puller to pull one out, much easier and quicker. then drift the other one out

If it's properly seized into the the inner bushes you'll have two options to remove it. Engine needs to be removed. Cut through the spindle each end of the swingarm, either with a disc cutter or a saw - obviously you have to be careful to avoid damaging the frame and arm. You can cut through the actual bush to keep away from the frame as they are going to be scrap anyway. Or you can drill dead centre each end of the spindle to depth that takes it inside of the frame and to a diameter just short of the spindle diameter. Now the spindle is 'hollow' a good tap with a hide mallet will break the spindle and the arm is out. Or you can just keep enlarging the drill diameter until the arm just falls out when you've drilled it away to just inside the frame Now you can cut the spindle either side of the engine mount.The spindle rarely seizes in the engine mount and hopefully just slides out. If not you might need a press or more drilling Now you have the swingarm free. Usually it is just the spindle seized in the inner bush that's the problem so the inner bushes should slide out of the outers with no problem, or they can at least be drifted out if stuck. To remove the outer bronze bushes, saw through the length of them on the inside on opposite sides so that they collapse and either fall or tap out. Again, you have to be carefull not to cut into the arm. Pressing them out can be difficult and can distort the arm

The taper referred to is at the top of the tube where it slides into the top yoke, what you see in the picture is normal for the bottom of the tube.

Probably, I've run 70s trials bikes including Sherpas for years, they run fine on premium fuel. I use V-power

Although I said I don't know about Avgas on your other post in terms of actual use, I do know it contains lead and therefore isn't allowed in trials as only unleaded is allowed (obviously no testing is done so no-one is going to know) However, you really don't need 100 octane fuel for a Sherpa, it runs fine on premium or super fuel. However, I'd avoid E10 due to the increased ethanol which could damage your tank if it's fibreglass (as you have a model M150 it could be an alloy tank) Just stick to premium fuel from the main brands as it contains little to no ethanol Trials engines, from that era especially, are low compression ratio which spend hardly any time on full throttle in comparison to road racing or motocross

The engine is dated in the same way, as from the factory the engine and frame numbers matched, apart from the letter prefix, so your engine is from a 1971/72 bike. There is no difference in performance between this engine and the original engine. Apart from the clutch cover they look the same. There are however a few internal mechanical differences so it is important you give the engine number when ordering parts I don't know about Avgas

The practical advantage of the flanged tubeless rim is that eliminates the possibility of losing air through the spokes which can happen on normal tubeless rims if the seal isn't good (I use silicon sealer instead of a rubber band, the type used on aluminium window frames) However, with some tyres either type can leak from the tyre bead so flangeless doesn't 100% guarantee that a tyre won't deflate slowly over days/weeks Others like them because of appearance which is just personal choice The problem lacing to a Bultaco hub is the length of the spokes on the sprocket side can be a problem. I've seen Fantics with them so it can be done. I think though that they are hard to find now. If you buy a used rim make sure you see it first as they can corrode on the inside so if there is a tyre fitted you won't see it, as outwardly they look fine

There is shortage of IRC, next batch is due at the end of the month. There's a shortage of most tyres at the moment it seems

It's the stroke

They're usually quite tight, helps to warm the piston and it should push out. You can also tap them out but you need to suppoprt the piston so that it doesn't get damaged against the studs and also that lateral force isn't imposed on the rod You can also buy universal pin removal tools which are quite cheap