feetupfun

So it looks like you have a TY175 rolling frame with 1978 DT175E wheels and engine. If you post photos of the complete bike and at least the first half of the frame number it will allow for an ID of the frame and the other components. As for the gearing, one of my TY175s had a 1981 DT175G motor (which is very similar to your motor) in it and first gear was fine for trials sections but second gear was like third gear on a TY175. It would be easy to get your first gear to work well for trials by selecting a suitable front sprocket, probably 13T with the 60 rear. I think mine with the DT motor was 12/54. Putting a TY175 gearbox into your engine is a lot of work and expense and if it was mine, I wouldn't bother because I don't use anything but first gear in sections and the DT gearbox makes it much better to ride between sections and trail riding. That DT175 motor is actually pretty good for trials use. The porting of the DT175 motor is pretty much the same as the TY175. The port timing is the same but the ports in the DT motor are more squared-off in the corners. The DT175 motor has higher compression than the TY175 which is something that some people do to TY175 motors to get more grunt. The standard carby on the DT175 motor works fine for trials. The biggest difference in the motors is that the DT175 flywheel is a fair bit lighter than the TY175 flywheel. Some people lighten the TY175 flywheel and for experienced trials riders the DT175 flywheel would be fine. For novices it would be a bit easier to stall with the DT175 flywheel.

OK based on you posting photos showing the backing plate at both ends of it's rotational adjustment range, I suspect that you might not be approaching the task the right way. Maybe I'm off track here. How about you say what you have tried doing so far and what the status of the points is? Are they new? Are they the existing points that worked OK earlier?

I've told countless people the same thing but I suspect that some people would rather have the excitement of riding on the ragged edge than getting the lowest score

Yes as long as nothing protrudes inside as it could damage the stator. It's a normal thing to undo the nut with an impact driver/rattle gun. As for tools to ergonomically hold it still while you tighten the nut, an adjustable two-pin wrench works on just about every magneto flywheel I've had to work on. I find it better than a strap tool. Something like this: https://www.maxiloc.com.au/product/amf-adjustable-pin-wrench-758/

It depends on which electronic ignition it is. Some suppliers will sell you just the stator coil. Yes, coils can be rewound but it might be cheaper and less trouble to buy a replacement stator coil if you can.

Sustained steep uphill does a great job. One of the places I ride has a decent hill with an incredibly steep concrete access road to a phone tower on top. The climb provides about 90 seconds of sustained load on the motor. Third gear on a trials bike. I like the replies you got from the oil supplier. It's good to know that they know about trials bike issues.

The rings stick in their grooves due to gum which is made of partially-burned two stroke oil. The rings then don't seal against the bore which causes lots of ring blow-by. The blow-by then forms a gum on the bore. When the gum cools it gets even stickier. All standard stuff for a two stroke that uses modern low smoke premix oil and doesn't get ridden hard enough to burn the oil fully. Either use oil that burns better or ride it hard once in a while or pull it apart and clean it out more frequently.

I've ridden a friend's '21 Scorpa 250 in sections and it steers and handles great and is very easy to balance on and the brakes work great and the suspension is lovely and the motor, which has a higher compression head, is quite responsive but easy to manage. The footpeg location feels great too and the clutch is also very nice to use. The bike also feels very light to ride. I like riding Shercos too. The owner of the Scorpa is pretty much exactly my size (5'10" 95 kg) and I can jump straight on it from one of my twinshocks and it instantly feels good and easy to ride so I would say that is a sign of a forgiving modern bike.

If your inner bush is worn or pitted, it will not work well with rollers

If you can get a properly hardened inner bush for the rollers to run on that that kit would probably be OK. I bought a similar kit to the one in you link a few years ago and fitted it along with a new (aftermarket) inner bush, but with only a little use, the rollers wore through what turned out to be very thin surface hardening. I think they would be fine with a new, genuine Yamaha inner bush The standard TY175/250 plastic bushings fit a very wide range of Yamaha models

re P.S. Yes. Go into your account then "settings" then "other settings"

Yes you can wrap it. You would not be the first. The negatives are corrosion, weight and appearance

It's so variable depending on the sort of riding in the three hours, but if that figure is for riding in a competition trial with a short loop and queues at most sections then it sound about right.

All the modern ones have small tanks standard but there are auxiliary tanks available (called long ride kit) that fit in the dip and have a bum rest on top. Standard tanks on some modern bikes need to be topped up during a one day trial. If your knees are really crook there are electric start kits available for some brands. There are proper electric trials bikes that run for ages on a charge and are great for stealth riding. Of course twinshocks have a huge fuel range and can be ridden sitting down and are very low maintenance. Bultaco and Montesa twinshocks can be very quiet. TLR200 Honda is exceptionally good for doing what you've described.

Crankcase cover - which side? which TY250? Kickstart - which TY250? Where in the world? New? Second hand? Genuine? Aftermarket?

Lean the bike over and if there's a ball it will probably slide out. If it doesn't come out using gravity, take the clutch pressure plate off, remove the mushroom and push the ball out from either end.

320mm to 340mm will work. Top mount position depends on what shock length you want to use and what the shaft travel of the shock is and how high you want the rear end

Very common mod to increase rear wheel travel and if you use the same shocks, raise the rear. Was standard on Yamaha frame Majesty 175/200. Lots of TY175s modified that way by owners in the 1970s and still commonly seen being done. There was a kit available for it a few years ago.

Measuring the peak pressure on a two stroke will always give variable results. Without changing anything else, the amount of oil at the ring/bore interface at the time of the test will make a significant difference to the result. Fitting new rings without honing the bore will make the results of that sort of test even more variable.

Somewhere within a very wide range depending how well the restoration was done

I wouldn't assume anything about a fuel tap

What's a side casting?

Hidrol was/is a brand of fork oil and the 7 means 7 WT

It's a fairly normal thing to shift to neutral before you come to rest if you want to then sit in neutral with the motor running. It will shift easily to neutral if you shift when there is no torque on the gearbox (ie motor not driving bike or bike not driving motor). It is quite normal for shifting to neutral to be difficult with bike stopped and motor running (clutch drag puts torque on the gearbox).

I suspect that the single piece WES design may have been improved at some point in time regarding how noisy it is, because mine does not sound like how you have described yours. I bought mine maybe three years ago through TYoffroad