feetupfun

Yes that's the A model cover. At times I've seen multiples of them advertised concurrently on eBay. Here's another one https://www.ebay.com.au/itm/74-YAMAHA-TY250-TY-250-A-OEM-LEFT-CASE-STATOR-COVER/202894542533?epid=1681129835&hash=item2f3d7506c5:g:Xx4AAOSw6PpeNMHi

If you are unable to find that cover, the A model cover fits and they are in plentiful supply

Those look like standard Cota 247 forks so they could be called Montesa or Betor-Montesa forks. I suspect were probably made under contract in the Betor factory in Spain for Montesa. They are slightly different internally to Bultaco Betors and OSSA Betors of the same era and the sliders are unique to the Cota 247. Ceriani brand forks were made in Italy but forks like those on your 247 are also known as Ceriani type forks because the internal design was originally developed by Ceriani and later copied by other fork manufacturers.

Yes the brass piece. I bent it about 45 degrees which was enough. You know that even if you did break it, it could be replaced with a piece of brass or copper tubing. Those vent fittings are just glued into the body of the carby. Another consideration is that the carby has a bowl vent on each side so it probably makes no practical difference if one of them is blocked off

I think I just bent the part the hose goes onto to give clearance. No money required

Those drawings in parts books often contain things that are misleading. I've seen a drawing in a parts book for the internals of the forks of one bike (maybe a TY) and they have drawn the springs unrealistically which can cause confusion. Yes there is a performance advantage if you fit an ignition that changes the timing to suit the engine RPM compared with the standard TY ignition that has fixed spark timing. A fixed spark timing is only perfect at one particular RPM and choosing what timing you run it at is a compromise for the rest of the RPM range. In the case of your bike the advantages would include less tendency to kick back when starting and more power in the mid to high RPM range. My seat-of-the-pants estimate for the trials bikes I've fitted them to would be about an extra 10-20 % power available in the mid to high RPM ranges. There are probably modern aftermarket ignition systems that also have stator coils for lighting.

The holes drilled in it are to balance it and were put there by the manufacturer. The steel ring/band on the outside of the "cup" of the flywheel does look to have been machined slightly narrower but it is hard to tell for sure with your photo. Trials two strokes generally have more flywheel effect built into the crankshaft than trail bikes and MX bikes. In the case of the TY250 motor the additional flywheel mass compared to the trailbike motor that the TY motor is based on is in the form of that steel ring fitted to the flywheel cup. The next and subsequent models of the TY250 twinshock have a bigger steel band there than the A model. Trials two strokes benefit from the additional flywheel effect because it smooths out the response of the motor at low RPM to changes in throttle input. This smoothness is important when riding trials sections to help with controlling the bike. The ideal amount of flywheel effect depends on the skill level and personal taste and riding style of the rider. The B and later model TY250 motors have a very strong flywheel effect which helped them perform well in the 1970s but since then the performance of tyres and the way we ride trials has changed so much that reducing the flywheel effect on those models is nowadays a popular modification. Back when the A model TY250 came out it was perceived as having a motor that was a bit too responsive which is why the steel band on the flywheel was made bigger. Nowadays the A model flywheel effect is seen as close to the ideal. When riding a TY250 on trails and roads, the additional flywheel effect of the TY compared with a similar motor in a trailbike with less flywheel effect is of no practical benefit.

Depends on the design of the cap and what it screws onto. Some use a o ring. Some use a flat rubber seal.

I'm the same weight as you and on my TY250 I've got standard damping Falcon trial classics with 50 lb springs and they are perfect for me. I don't hop the rear but if that is your intention then you would be better off with the superlight damping version.

To shift gears with bike motor off and cold, rock the bike forward and back while you hold a steady force on the shifter. The status of the clutch is not relevant when shifting gears cold or hot, but the transmission needs to be unloaded to change gear.

Cross referencing on the part number shown on your brake shoes (5007) indicates that they are aftermarket brake shoes that fit the rear wheel of a KYMCO 50cc 4 stroke step-through scooter

Have fun, but don't do it for my benefit. I've been through this particular hoop many times already

When I put a KT250 VM26 Mikuni on my Cota 348 (MK2 AMAL concentric) I made a spacer ring from plastic electrical conduit which just happened to have the perfect diameters.

I found the same thing using a HT lead-triggered strobe on one of my DT175H motors with standard Yamaha electronic ignition.

They aren't fatigue cracks. If you look around, you will see the same sort of marks in other parts of the engine that were made the same way (die casting). You are not the first person to think that they are cracks.

If you are using a 21" front wheel you may need to have a think about what the trail will be when combined with the KX85 triples. You should be aiming for about 90 mm trail

about 26/27 degrees

Yes, you would need to find a stator coil in there that is not part of your ignition system.

OK my experience with electronic ignitions for TY twinshocks is with three types: Trails and Trials UK Rex's Speed Shop Electrex World I've got two bikes with the Trails and Trials UK ignition and never had a problem and neither of them has ever kicked back. I also have a TY250A that still has the standard ignition system working perfectly and it kicks back a fair bit when I'm knackered during a hot trial but not when I'm fresh. Both the bikes with the T&T UK ignition run very well. One of them was fitted to allow the timing to run only a small advance at low RPM to tame the motor response down at low RPM yet still run well through the RPM range. The other T&T UK system was fitted because I was having problems with the original points ignition cutting out unexpectedly. I've ridden a friend's TY250A that had been recently rebored and had a Rex ignition fitted. It was similar performance at low to mid RPM compared to my TY250A that has the points ignition system but from mid-rpm to high RPM it had noticeably more power than mine. I helped a friend to fit an Electrex World system to his TY175 and was amazed to find that the mounting location for the HT coil was beside the airbox. This means that the HT cable passes over the carby and past the fuel hoses. The bike ran fine with this ignition. They may have found a more suitable HT coil by now.

Sorry but to reduce kickback while kickstarting you should run less advance not more advance.

I already said you could fit an electronic ignition with advance. This will give you less advance at kicking speed. If still using points, set the timing with a strobe light. Be patient. Lie the bike on its side. Wear a head light that shines from between your eyes.

The rim might not have the correct offset from the hub

Yes of course you can fit the diode. The rest of the TY250A ignition is the same as the later models. However the diode is there to stop the motor running backwards. It won't stop it kicking back which is caused by firing prematurely with the crankshaft turning in the forwards direction but too slowly. The tendency to kick back is made worse if the spark timing is a bit too far advanced. If you want to minimise the possibility of a kickback then use an ignition that has an advance curve.

Have you asked Richard Kent (the aussie EM agent) yet?

If it has the original setup inside the magneto cover, probably not, but you would have to remove the magneto cover to have a look to know if it is original and to know if it has a lighting coil. Another thing you could do, to help people help you, is to mention what digits the engine number starts with so the motor can be better identified.