feetupfun

Remove all the screws. Remove the kickstart lever and whatever else might be in the way. Lay the bike over on its right hand side with the cover you are about to take off being parallel with the floor. Carefully ease the cover up a tiny bit and make sure that the gasket stays on one surface or the other, to avoid ripping it. That way you might be able to resuse the gasket. Once the gasket is sorted, remove the cover fully. Oil will drip off it.

You can use WD40 to mount the tyre instead of a water-based lube

Another way for water to get into the gearbox oil is by riding through water

The symptom is water in the gearbox oil. A head gasket leak cannot cause this

There are two clutch covers. The outer one that you have removed is for working on just the clutch. The bigger cover surrounding that cover is the one you need to remove to work on the water pump drive shaft.

Is that the electric works special?

The sliders do not have replaceable bushings. The tubes run against the slider bore directly. Sliders can be machined out and sleeved/bushed. The screw in the bottom is what holds the forks together. The spring clip only retains the seal in the slider. Forks jamming at the bottom of the travel is not usually caused by worn sliders.

The points stay open for a while. The important thing is where the piston is when the points start to open.

You can fit 50 lb Falcon springs to those shockies without modification. They are available as a spare part. 340mm shock length is fine no matter what springs you use on the shocks. So are 350mm shocks. So are 360mm shocks. If you go longer than 360mm shocks you may need to do some metalwork to let the swingarm rotate down far enough. 340mm is probably the ideal length for what you do with the bike. There are many ways to change the spring preload. One way is to take the spring off. You can then move the spring steel clip from one groove to another. This clip is held in place by the top spring retainer so by taking the spring off you can slide the retainer down to expose the clip. You will need a pointy tool to get the clip to move out of the groove. To take the spring off you take the shock off the bike, compress the spring and take out the bottom spring retainer. Another way is with the shock still on the bike. Grip the top end of the spring in one hand and pull it down away from the top spring retainer, slide the retainer down a bit and keep holding against the spring while you move the clip from one groove to another. There is a risk of pinching fingers doing it this way, but it very fast once you get good at it. It is easier doing this with two people. It's quite normal to have to use one of the lower grooves when you use 40 lb springs on Falcons on a TY250. Trials bike suspension is intended to be very soft compared with other types of dirt bike suspension so it works well in sections (low speed with the rider standing and legs forming part of the "suspension"). If you ride a TY250 that is set up to ride trials sitting down and go through a dip at speed, it will bottom out the rear suspension heavily.

No problems with pressure build-up and no vent valves fitted. The oil height is set to give the air spring effect I want when forks have reached normal operating temperature

Sealing off the vents allows for easy fork spring rate tuning by changing oil height if you are into that sort of thing. The KT250 came with vented caps too and the oil deflection technology in them is quite clever but I still replaced them with sealed caps so I could tune the fork spring rate.

The silicone I put there 15 years ago is still doing a fine job

Welcome and may your ribs heal fast

Lowering the footpegs lowers the C of G of the bike (when there is a rider aboard), making balance easier

If the lever end is too far forward in the stored position, the "cam" can go too far around while kickstarting. I run with the lever a long way forwards but manage the situation by letting my heel hit the footpeg so I dont rotate the kickstart shaft too far. If you lend your bike to other people, this method of avoiding damage to the magneto casing is not recommended because it is all too easy for someone not familiar with the bike to over-rotate the kickstart shaft. If you pull the magneto cover off and have a look at the kickstart shaft, all will be revealed

Modern stripper also burns if even the tiniest dot sits on your skin. They changed the makeup of stripper to make it harder for people to use it for malicious purposes. The main difference is that it is now a gel instead of being a liquid.

The modern (solvent type) paint stripper here works fine on metal but you do have to use it differently to the old type. It dries very fast so you have to work small areas in sequence rather than coating the whole thing at once

The modern aftermarket TY250 footpeg kits have the footpad slightly lower than standard and back a little bit which makes it more comfortable to ride sitting down compared with the standard location and better for trials too. The TY Trail kit footpeg location is terrible for trials being too far forwards, but is probably the most comfortable for riding while sitting down.

Next time when you put it into 1st gear from neutral with the motor running, while your foot is still holding the shifter down, let the clutch out a little bit and you will probably find that the shift lever drops a little bit further (and there is a clunk). That is signalling that it is fully engaged in that gear. The clunk you have described with your 349 is the bike finally going fully into gear and is a fairly normal thing with 348 and 349 Cotas. If you can select all the gears and it stays in a gear once fully in gear, your mechanic has done a great job.

Those extra washers on the outside of the frame plates are unusual. Possible reasons are: Your swingarm pivot axle may be a bit too long. The trail riding kit for TY250s may have included a longer bolt to suit the trail riding footpeg mounts being attached at the swingarm pivot, and your bike may have one of those axles. Previous owner thought it would be a good idea to spread the forces. Is there damage at the holes in the frame plates? Shims: Shims are used if the width of the swingarm is less than the distance between the frame plates. Some bikes match without shims and some bikes need shims. Holes in the inner tube: Yes, original inner bushes have holes and if you loosen the swingarm bolt before using the grease nipple then you may get some grease to flow into the space between the inner bush and the axle. However, because you can slide the axle out to grease it or to apply anti-seize, the holes are not necessary. They also serve to lighten the inner bush. If you are serious about lightening your bike, you can buy ready-made aluminium inner bush and aluminium axle.

Yes all TY250 twinshocks have the same heat shield, just decorated differently. The flat section is 122 mm x 19.5 mm

https://trials.com.au/forum/viewtopic.php?t=5545

https://www.inmotiontrials.com/product/bultaco-red-tank-frame-paint/

https://www.ebay.com/itm/Montesa-cota-349-white-fuel-tank-and-new-seat-/292556986104