feetupfun

You got me wondering if I was imagining USD forks on my friend's bike so I went looking for photos. Here are a couple of photos of my friend's 2001 Rev 3 270 showing the USD forks that it came with (the bike that you have been told none were brought into Australia). Photos taken in 2004 or 2005 when the Queensland Trials Titles were held near Dayboro. From memory the first owner was Kris Hammond. Second owner (shown in photo) was Ken Cutmore.

A friend of mine had your model Rev 3 with USD forks and it developed more sag than normal and he discovered that the fork spring was broken. If yours is a 270 it might even be the same bike. My memory is telling me that those forks were standard on the first model Rev 3 and were optional on the second model Rev 3. Yours looks like the second model which I would call the 2001 model. This is what the first model Rev 3 looks like

I don't think it will have an oil filter. If it's like the Jotagas bikes I've seen they are two strokes. Normally only 4 strokes have oil filters.

Wow that's amazingly original after all the years. Good find and great to see. Thanks for the photo. The absence of external damage and wear makes me think it must have been parked up somewhere for almost its entire life so far. The tyres look like 1970s type. I bought a TY250 in this sort of condition in 1994 and was amazed at how unused and undamaged it was at the time but that was 26 years ago so yours is even more surprising.

The A model fits yours and the BCDE covers are all the same. Either cover suits either flywheel on any engine. They changed the cover design to make the motor look slimmer after initial criticism of the width of the A model engine and also to help keep the bike at the same weight despite the heavier flywheel. The BCDE cover is magnesium while the A cover is aluminium. Other weight saving changes to keep the weight the same with the later, heavier flywheel were aluminium brake arms, magnesium clutch cover and oil pump cover and an aluminium fuel tank. If you do get an A model magneto cover, a BCDE model shift lever will probably not suit the shape of the A model cover.

and another one https://www.ebay.com.au/itm/1974-YAMAHA-TY250-TY-250-Stator-Cover-Mag-Cover/362581712843?epid=1681129835&hash=item546b8ddfcb:g:2DoAAOSw~Tdch9zo

and another one https://www.ebay.com.au/itm/1974-YAMAHA-TY250-TY-250-Stator-Cover-Mag-Cover/362581714795?epid=1681129835&hash=item546b8de76b:g:618AAOSwrERch93A

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.