feetupfun

If it helps, I had one of those diodes on my TY250D and it kicked back just as easily as my other TY250s that don't have diodes. I took the diode off the D motor for an experiment when I was diagnosing an ignition problem (that turned out to be a loose bullet connector on one end of the diode) and it still kicked back exactly the same. To improve your success rate when kicking it to start it, ease the piston up to as near to TDC as you can, either a bit before or a bit after, wherever it will stay still, but not too far before or past TDC. You are doing it slowly so it doesn't fire or go too far past TDC. Then let the kick lever return to the top and then give it the start kick. Keep full force on the kickstart lever as you move it, all the way till the lever hits the footpeg. That technique puts momentum into the crankshaft and flywheel before the piston gets to the firing position, so when it fires the motor will keep rotating forwards. People like me who have been riding these bikes for 45 years do that thing I described on autopilot, very quickly and don't even consciously think about it.

About your first question, no there was not a factory option to have Ty175 pegs further back. The kits to move them back and down a bit came much later and not from Yamaha. The TY250 did have a Yamaha kit that allowed people to have the pegs further forwards for trail riding

Some kits require the RH peg to be lifted to kickstart the motor. Some don't. I haven't seen anyone move the brake tip back to compensate the the peg being further back. The kit I've got doesn't move the pegs back far enough to make much difference and is quite a comfy reach to the brake pedal tip (size 11). The brake lever tip is adjustable fore and aft by reshaping the front end. It's a fairly common task to reshape it after hitting things with it. If you are still in doubt I will take some photos showing the distance with kit pegs

It can be fixed a few ways but what is the point unless you are going to stop riding it

Betas make a whirring noise even when everything is working perfectly because they have straight-cut primary drive gears. My 1976 KT250 also has straight cut primary gears and also makes that great sound. When your mains fail if there is any noise it is a rumble. Beta mains usually last for many years of normal trials use.

There is a reason why they leave the shields in. In the 1970s the Japanese two stroke trials engines had a ventilation system for the main bearings. There was a little port leading from the mouth of the crankcase to the space between the bearing and the crank seal (on both sides usually). Suzuki is an exception with their fancy CCI system on the drive side bearing. The Spanish trials bikes of the 1970s don't have that ventilation system. Guess which bikes the mains lasted for 40 years and which ones didn't last that long at all. Anyway, the bearing ventilation idea was ditched when brands like Sherco decided that a super-slim engine was worth sacrificing main bearing life for (the ventilation ports took up valuable space between the bearings and the seals). The first Shercos had a reputation for the main bearings lasting only a short time (one season) and this didn't go down well with owners so they tested the idea of leaving the bearing shields in place and found it gave a longer life to the mains. I'm fairly familiar with 1970s Bultaco motors (which have no main bearing ventilation) and from what I've seen when pulling them apart to replace the main bearings (which is every Bultaco I've ever owned), the bearings appear to have failed due to the balls and races having to continually squish little bits of carbon.

Leave the chain on and you can jam the wheel to hold the sprocket still to undo the nut

That screw has an offset pin on the end so you can adjust the angle of the clutch arm to offset for wear in the plates and mechanism. The offset pin lifts or lowers the clutch camshaft and the cam face is slanted to provide the adjustment

what is the history prior to the lack of spark?

Looks fabulous

You are welcome. I took a series of photos of three different cylinder types many years ago when I was helping someone work out which model cylinder they had on their TY250

Jeff what number is cast into the port side transfer port area

Here are photos showing my early 434 cylinder

It could be something as simple as the rim not being centered (spokes adjustment) and you can measure that. Don't measure from the tyre, measure from the edge of the rim to the fork slider on both sides. No matter what hub or yokes you have, the rim needs to be equidistant from the sliders and mudguard brackets. If you are still worried if it is standard or not, post up a photo of your front end and you will soon find out.

Its fairly normal for 1970s Montesa 247 and 348 clutches to shriek and squeal if the oil is too light. If you want it quiet and smooth you will need something heavier than ATF. I run Castrol VMX80 in my 348 clutch and it is silky and quiet and doesn't drag or slip. No I don't know of anyone selling new, genuine clutch plates for a 123. I'm sure Peter Schoene could get you some. I bought some 1970s Honda CR125 friction plates years ago to try in my 348 but have not got around to it. They will fit the 348 basket but from memory only drive on half the number of tangs. I've not worked on 123s or 172s so don't know if they run different plates to the 200/247/348/349. As for internal adjustment, there is an adjustment on 247s and 348s that works by choosing from various length brass plungers that bear on the three-legged spider. You could also adjust it by using different thickness gaskets on the clutch cover. Again I don't know what is in a 123. You can buy reprints of owners manuals from Southwest Montesa in the USA

Hi Andrew and welcome from another Aussie. You aren't the first person to wonder why things were done some weird way on an old Spanish trials bike. They are like a treasure trove of entertaining design features. Sorry I can't help with the Cota 172 oil quantity but I'm sure that someone can and owners manuals are available if you are stuck. About oil level checking, there are not many old spanish trials bikes with that facility and not all of them even have a filler plug.

I've got an unmolested early 434 model motor (never even had the cylinder head off) that I can take photos of, but I suspect that there are actually two different cylinders that came on the first model TY250 so that might be what is causing confusion. One type has a circular un-finned section above the exhaust port. Is that the type of cylinder you have?

Yes they work well on a trials bike and while they may not meet the rules in some places, no-one has objected to people using them in competition where I live. I wanted to run one on my Alpina but the local KTM dealer wasn't able to supply them. The people I know who do run them on their trials bikes have sourced them from KTM dealers who took them off Freerides at their customer's request.

The Yamaha heat shield fitted after straightening the curve and elongating two of the holes. Since I bought mine the design has changed so the nuts might not be in the same place as mine

Here's mine

Generally the longer the header the more evenly a two stroke motor will fire at low RPM. On 325 Bultacos this is quite important and a longer header makes them smoother, but then again so does packing the muffler properly or fitting a reed valve. On a TY175 the low RPM running is ridiculously smooth and even already. Having said that I recently fitted a long header to my 210cc TY175 in conjunction with the tyoffroad one-piece exhaust and it feels even stronger at low and mid RPM than with the standard type exhaust and it revs out better too. All I really wanted was the weight savings with the new exhaust so the way it runs is a bonus, but it may not be just due to the long header because the new exhaust is quite different in internal design to the Yamaha exhaust

Wiggle the clutch arm while you are trying to turn the clutch arm adjusting screw anti-clockwise. There may be a burr on the peg on the adjusting screw that is catching. If you are in doubt about what I'm saying, have a look at a parts diagram and you should be able to see how it works

Sounds very odd. That key shouldn't see any force if the taper is holding properly

You unscrew the clutch arm adjusting screw which is located in front of the sprocket

If there is not enough air space when you put the cap on, the pressure relief device will let out some coolant as the coolant heats up and expands. As it cools, the vacuum relief device will let some air in. If you leave it at that, you shouldn't lose any more coolant