feetupfun

Maybe the cylinder studs or their aluminium nuts have stripped but that is unlikely. Maybe you have lost some of the cylinder base gasket. Maybe a leaking cylinder base gasket caused the initial runaway. Stripped head studs will not cause the barrel to move because the barrel is held in place by 4 (cylinder) studs at the bottom. I'm interested to hear what happened once you work it out.

Don't normally need hot air gun for Bultaco unless someone has used sealant on the centre gasket. gearbox output sprocket and seal spacer cylinder shift drum external mechanism shift drum indexing plunger all the nuts and screws - one screw is tricky to see

That means the frame is from a Bultaco model 199A. The 7895 in the number means that is the 7895th one made. The 199A is a Sherpa T 350 nominal capacity 326cc and made around 1979. Blue frame and blue plastics. The model before it is a 199. The model after it is a 199B.

There's a few possibilities here. Most likely is because you have wound in the idle speed screw, the slide might be too high for the start device to function. If it's a modern carb, the starting device is not a choke. Modern starting devices use the pressure difference across the slide to draw fuel through the cold start circuit and if the slide is too high, not enough pressure difference will be generated while kicking, to draw fuel through. If winding the idle speed screw back out again doesn't solve the problem, narrow the range of possibilities by putting a couple of drops of fuel into the cylinder via the plug hole, then see if it fires.

The tank seat shown on the B&J Racing page is fibreglass and is a Sammy Miller Products tank seat and may be old stock. When you said the A model is lighter than the later ones, do you mean the whole bike or the fuel tank? The CDE models have the lightest rims, being Japanese copies of the lightweight AKRONT trials rims. The A model have lightest swingarm. CDE swingarms have more elaborate gusseting near the pivot. The BCDE flywheel is much heavier than the A model. The BCDE engine covers are lighter than the A model. The lightest tank I've found is a Majesty shape made from very thin aluminium. I bought it from France Trial Classic in about 2008. It dents very easily. I'm not sure if they are still available, but there is/was an aluminium steering stem/axle available. It is a lot lighter than the original. Also the top bolt and slotted nut for the steering axle. There is/was an aluminium swingarm inner bush available. I replaced all the wheel axle spacers with aluminium items.

For a slimmer look, you could fit the later model seat and rear guard. For an A model frame, this would need some frame tabs added for the seat mounts. The A model airbox is compatible with all known seat/tank/mudguard options. What you wrote about the airbox forming part of the rear guard applies to all TY250 twinshock models. The A model (and B model which was not sold in the USA) rear mudguard arrangement going from front to rear has airbox then seat shroud/fairing then short plastic mudguard. The C, D and E models have airbox then long plastic mudguard. If you want to use the Shedworks tank/seat, you will need to buy a later model rear mudguard. As for buying a later model (long) rear guard https://www.inmotiontrials.com/product/ty-250-rear-mudguard-white/ If you want it to feel lighter to ride, replace the standard exhaust with a WES exhaust. The later model TY250 fuel tank is made of aluminium and is lighter than the steel A model TY250 tank.

This is the type of decompressor that I was talking about https://www.ebay.com.au/itm/396896802024?_skw=chainsaw+decompressor&itmmeta=01K0ZH12R481E2RVX4FJPX53WW&hash=item5c68e494e8:g:r64AAeSwADxoggVl&itmprp=enc%3AAQAKAAAA8FkggFvd1GGDu0w3yXCmi1fLhVZ9pCnvxIEPuRqCU3B2ZOAfu9fy6%2F6WgF9a6nbXFSfm57hpL5lTOdssTnqBqUtKOtg33LWZbPrilBksRs681ExCGS7r9NYQKVprn4dpc3rDt2MLuIUhoplS8KeKoG1yKz1BTpjNWGXROZIiqD5Aw1sgDp8jlUjyMeJgiuDjXyxLCuEhPWJtHchCLtFwW2HfMHYcbdS6eai7IxU1bEM1KfPbA90mS5LOqQrBb4pYLuX0yd5%2FwRmkeWs0IOCsxf4KL6zTUS7U64O4ELHLH%2BZrDtsaoBvJlGKgMuy9BB48rQ%3D%3D|tkp%3ABk9SR_ashPGHZg

There are two forums on here where you can ask Cota 200 questions. One is "Twinshock" and other is "Montesa". There are also facebook pages for Montesa motorbikes.

Your statement "this is my first time riding a trial bike" tells me that the bike may be working normally, because 2 stroke trials bikes like your TY mono are very different in engine performance and gearing to 2 stroke non-trials bikes. How about you post up a link to a Youtube video of you riding your bike so people can tell you if there is anything wrong with the bike.

Do you have continuity for the earth side of the ignition system? This relies on a good electrical connection from motor casings to frame and from frame to HT coil.

Assemble the piston on the rod, mark up the piston where it hits then remove the piston and remove enough on those corners to give clearance of at least 1 mm. As for physically removing metal, hold the piston without deforming it and use a file or a grinder or a sanding belt or a sanding disc.

Maybe a previous owner modified it to suit a different axle. If the hole is 12mm, the original threaded hole may have been drilled out and bushed to suit a through axle.

I've got a model 49 250 Sherpa T motor and a Campera 175 motor available. Both require overhaul. Location Gladstone, Queensland Australia

other options include WD40 and dishwashing liquid solution

Tubed Trials tyres usually go on and off so easily using hand levers I don't usually bother with lube but if I was using a machine to fit one, I would use lube to make the sliding part move nicely. I do use lube when changing knobby tyres with hand levers because they have such a stiff construction.