feetupfun

Well I know that they didn't change the steering angle from go to whoa and will go and measure soon

New aluminium under tanks are available for the slimline Bultaco tank

UK Montsas usually have an aluminium tank inside a fibreglass cover. I'm sure you could get one of the aluminium tanks and use your tank to make the cover from. Sorry I don't know the road-legal status of fibreglass tanks in the UK in 2017

Keep the spokes tensioned nicely with that hub because they are known to crack around the spoke flange if the spokes are not kept tensioned properly. I'm not sure if it is the Honda hub from that photo, but the later model Montesas had them and it looks like one from what you can see.

The bashplate is not the original one and doesn't fit very well. I wouldn't worry much that it is not working as a stressed member with those rear mounting clips like that. The motor castings are easily strong enough to act as the frame member as long as the engine mount bolts are kept tensioned and you are not planning to ride at world trials championship level or race it over the jumps on a modern MX track.

Front wheel looks like a later model Montesa Cota that has a Honda hub (from after Honda bought part ownership of Montesa~1985 maybe)

Carby and forks and frame look right for a 1981 349. Front wheel having a gold rim means it is from a later bike. I'll have another look at it

I thought the fork sliders changed too

Probably better to measure the distance between the axle centres with the steering straight, because some people move the mounting points for the rear shocks

434 -00*** is A model (1973/74) The frame geometry on twinshock TY250s was unchanged through all the models. I would measure one of mine that I know is completely standard except I can't work out what you are calling the lower front shock mount

Test for it being a "too-lean" issue by next time it won't restart when hot, engage the starting circuit (the "choke" lever). This will help it to hot-start better if it is a little bit lean on the pilot jet. Similarly kick it with throttle fully open and "choke" off to test if it is flooding the engine somehow when stopped. Another thing to do is to fit a clear fuel line or a clear in-line fuel filter so you can see if there is a problem happening with fuel supply to the carby bowl when it is hot and stopped. Beware that sometimes a float valve will work fine while the motor is running but stick open or shut when there is no vibration. Another thing is that a leak at the ignition side crank seal will not reveal itself as smoky exhaust

My favourite is someone saying their TY250 is totally original and never been worked on, and the aftermarket replica front mudguard is fitted backwards

Do the papers have to be for a MH200 that is registered in Germany or would rego papers from another country be OK?

Do you mean you want identification papers as a way to prove the age of the bike?

Manuals for these are available from http://www.southwestmontesa.com/manuals.html

Have the drive dogs on the gears ground to help stop it jumping out of gear (if they are worn)

This is a fairly eye-opening and entertaining thread To answer the original query you should stick with the fuel that Honda recommend because "race gas" burns too slowly for a standard 4RT. The problems with burning too slowly are that it causes high exhaust gas temperature and the motor produces less power

I find with the standard Ty250 frame you do need to be over a certain height to be able to lower them by much without it becoming a problem. I'm 1760mm 5' 10" and have a Ty250 with standard frame that I mounted them in the position you have done and found that my coccyx sometimes hit the bike behind the seat when unweighting the rear on obstacles. I figure I would have gotten used to how far I can unweight if I only rode the one bike. It did change the handling a lot

248 is a much better motor for mortals

If everything is perfect it will be no better or worse than a 1985 TY drum-front-brake mono was when it was new. If you had to take lining material off to get full contact, it means that the drum is probably a bit big in diameter and you probably now need to pack out the pivot ends of the shoes to minimise the cam angle. If the drum surface is grooved or uneven they will never work well no matter what you do. It's normal practice with people wanting the best front drum brake they can get to machine the drum smooth, have oversize high friction lining material attached to the shoes and then machine the shoes down to match the diameter of the drum, using the backing plate to hold them in position in the lathe

lean the bike over

Yes a fine line with the backpressure. Too much and it will be RPM limited, too little and it will have less torque than ideal at low RPM. It should go heaps better (for trials) with an end muffler or a stinger compared with having nothing on the end of the main chamber

I can say that TY250 TS is sensitive to exhaust backpressure and you can also have fun experimenting with the length of the header pipe (just like any other trials two stroke) You should know what you like before you start experimenting. The standard Yamaha TY250 design works well but is pretty heavy and the end muffler makes a terrible sound Some people prefer the 74 model engine over the later ones, so again it would be good to know what you want

I'll have a go at interpreting these metaphors from the other side of the earth "A degree of marketing?" = writer is indicating in a sarcastic manner that they would attribute a low probability of being able to convince potential buyers about the benefits of buying a side-valve trials bike "What like if this pig can fly you'll need a 1/4r of a ford pop for trials?" = If this unlikely concept were to succeed in the market, then potential buyers would need to believe that it was a good thing for a trials bike to have similar engine characteristics as an obsolete British road car or van that had a four-cylinder side-valve petrol engine

Need a better photo if you are serious