feetupfun

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

The KT end muffler now has a perforated tube that runs the full length of the casing with loose wool packing attached to the tube with steel wire and has a long radius 90 degree bend of the same diameter as the perforated tube welded to the outlet, pointing downwards. The perforated tube was cut from a 2 stroke go kart muffler core.

Yes the WES is noticably quieter than the standard TY250 muffler, and it is a much more pleasant tone as well to many people's ears.

I'm like that with the noise level too. I've a nice practice area at home but there are houses within 50 metres, so I have been quite persistent in getting my bikes as quiet as I can so I can practice without annoying people. One of my bikes is a Cota 348 with standard (repacked) exhaust system and it is blissfully quiet to ride. Late model Bultaco trials bikes are also amazingly quiet with the standard exhaust. With a bit of work you can even make Japanese two stroke trials bikes quiet. One thing I noticed about a WES muffler I have on a TY250 Yamaha with standard main chamber. It is nice and quiet both through the walls and at the muffler exit, but if I put the same WES end-muffler on my KT250 (also with standard main chamber), there is a lot of noise at the exhaust exit of the KT. Because of this I have re-modelled the internals of the standard KT250 end mufler to make it quiet enough to ride at home (and so I can hear the whining primary drive gears better) One of my TY175s is a Whitehawk with a standard Yamaha front exhaust section and the end muffler is from the super-quiet TY175JC that was fully road registerable after the noise-limiting Aussie vehicle design standards came out in 1976. The TY175JC also had a rubber snorkel on the inlet of the airbox which further quietens this bike. The engine in this bike has just been restored so there is no mechanical noise to speak of and overall it is a very stealthy bike.

In answer to your question about the tailpipe insert. Don't do anything to the exhaust that will change the backpressure because it is fairly critical for how well the motor runs. Too little and the low end response will be poor. Too much and the motor may develop detonation problems when it is hot