feetupfun

Some models don't have an exhaust port bridge so don't benefit from having holes there. One of my Bultacos is an Alpina 138. It has no exhaust port bridge, but the only piston I could buy at the time I had it rebored (about y2000) had those holes.

OK I see the O ring you are seeking in the A model parts book showing the TK carby. Yes, if it leaked, some fuel could bypass the main jet.

The 26mm OKO from mid atlantic trials is fabulous. I've got one on a TY250B motor, replacing the original Mikuni which had seen a lot of use. I haven't tried the OKO on my A model yet.

pmk, I figure you are enjoying the process of developing your Curnutt shocks to the point of getting them working well for trials use. It is quite interesting to hear your voyage of discovery. As far as shock lengths go, the Betors that came with my OSSA are 350mm long and TY250 twinshocks originally came with 325mm shocks. Most people nowadays ride TY250s with something between 340mm and 360mm and my OSSA steers nicely with both 350mm and 360mm shocks. The reason why trials shocks in the 1970s had shorter travel and heavier damping than trials shocks do in 2017 is because the development work that has produced the amazing trials shocks we can buy now, hadn't happened yet.

yes count grooves starting at the top. When you say the "needle jet set screw", I figure you are meaning the air screw. As well as the diameter, measure the groove width and depth to size the o-ring. A leak past the air screw o-ring will not make the bike run rich. In a TY250A TK carby that has had a fair amount of use, a likely cause of the bike running rich is: Wear in the needle jet and the needle (where they rub against each other) or a passing float needle valve

I've got an A model like yours and the motor has never even had the cylinder head off, but a few years ago when I was servicing the points, I did notice a small oil witness around the magneto side crank seal. The main bearings were still quiet and with no detectable free play, so I assumed that the seal had just started leaking a bit because it was so old. The motor still ran fine and if I hadn't looked would not have suspected that there was any leakage there. The crank seals on both sides can be replaced without splitting the cases. If that was my bike I would inspect the magneto side crank seal for any evidence of oil residue, feel for any up-and-down play in the LH main bearing and have a good listen with the motor running for any rumbling noises, which are a tell-tale for failing main bearings. They are an incredibly sturdy motor so can do an amazing number of hours of regular use with little effect on the bearings, but like any two stroke, any rolling element bearings on the crankshaft assembly can be damaged fairly quickly from the bike being stored in damp conditions. If there is any up and down play or rumbling, it is not worth changing the seals unless you also replace the main bearings, because the movement of the crankshaft will probably cause even new seals to leak

Those bars are what came standard on the first (1976) and subsequent Cota 348s. They are 1" in the middle and stepped down to 7/8" for the lever mounts and grips. They have a nice shape but beware of unexpected failure. Mine looked perfect externally but broke unexpectedly in about 2014.

When you say "The big end pin won't allow the crank webs to close that side play down even more", are you saying that the big end pin is stepped?

That one looks like a Fraser frame with a Bultaco front end (Sherpa T triples, Bultaco Betor forks and Alpina/Frontera front hub)

A standard TY175 carby mounted on a TY175 should not have any problems due to riding steeply downhill if the float height is right and the float valve is sealing off. They normally work perfectly. The float valve does not last forever. I think I'm on my third float valve in the TY175 I've had for 41 years. If it is a wear problem causing the valve to pass, you should see a band on the needle surface that is not shiny (where it touches the seat) and the rest will be shiny. The needle taper should be shiny all over. If the problem has developed over time, it will probably be the float valve passing. If you don't know the history of the problem, it could also be that the float height has been set wrong.

It's fairly common to need to open the fork tube clamps a bit. If you've had the tubes re-chromed sometimes they end up slightly bigger in OD than original, but even standard tubes sometimes need it too. If it is only the second (upper) clamp that is causing problems, it might pay to check if either of the clamps is not quite straight. Another option is to fit the tubes through the bottom clamps without the top clamp, then fit the top clamp, rather than try and slide them through both clamps at the same time.

Common failure on that type of hub. It is a Honda hub and good ones are rare, not just because it is a rare model bike, but also because they break). Cota 242s also had that front hub. The earlier Cota 247/348 type front hub can be used and are far easier to find. I've also seen Yamaha drum-brake wheels fitted to 348s and 349s. Some 349s have narrow spacing between the fork tubes which limits the type of hub that can be fitted (unless you also get a set of wide triple clamps)

The rim and tyre should be in the centre between the forks. The rim can usually be moved left or right by adjusting the spokes. It's possible that it has a non-standard wheel so if you post up photos, you will get help with that.

How the air screw is set makes a big difference to the off-idle response

On the SWM in the photo there is still cable between the clutch and the device which would operate at full cable loading. Your suggestion to have an intermediate lever just above the clutch cover with a rod to the clutch arm would have less friction overall than the setup on the SWM because the whole cable run would be operating at reduced loading.

Have you tried Hell Team (GasGas importer and a wealth of GasGas knowledge) in Sydney, Australia? I think they helped my friend out who bought either rings or a piston kit for their GG70

The green is the 212 (250) and the red is the 213 (350)

Sammy Miller Products made some a couple of years ago

Here is the page from the parts book for a TY250C which lists that (output) shaft as the same part number as a TY250A. I notice that the clutch (input) shafts have different part numbers.

OK I have tried a few things out on my KT clutch in attempt to reduce the lever pull by reducing the pressure plate clamping force. First I inspected the clutch and read my log book. The friction plates are genuine Kawasaki KT and about 10 years old and low hours. New genuine Kawasaki KT springs were fitted at the same time. The drive edges on the friction plate tabs were smooth. The basket fingers are steel and were smooth. The rack and pinion had a smooth action and was well lubricated. The cable is a 10 year old Venhill and was well lubed. I think I could improve on the cable by making it a bit shorter, to improve the routing. The gearbox oil is Dexron II ATF. After that, the first thing I tried was to reduce the clamping force on the pressure plate by reducing the clutch spring preload by spacing out the spring retainer plate. I found that reducing the preload by 2mm made barely any difference to the lever pull. I also found that 2mm is about all you can add there before having to use extra clutch cover gaskets or machine something. Next I went looking for alternative springs and found that some springs that came out of a TY175 motor were very similar to the KT springs, but a bit higher spring rate. The KT springs were 165 lb/in and the TY175 springs were 186 lb/in. This meant that six KT springs would theoretically have a clamping force of 779 lb and four TY175 springs would have a clamping force of 585 lb, or 75% of the force it had with the six KT springs. Four KT250 springs would have 66% of the clamping force of six KT springs. I fitted four of the TY175 springs and tried it out and found it worked fine in all gears and the lever pull was noticeably less, but still not as light as my TY250 motors with their three springs. I am running very low gearing on this KT and suspect that if it had standard gearing it might have clutch slip in the upper gears. KT 250 springs 15mm OD, 7 coils, 2mm wire, 31.5mm free length TY175 springs 14.4mm OD, 7 coils, 2mm wire, 31.1mm free length By the way, those springs that came out of the TY175 motor might not be standard TY175 springs

maybe post suitable photos so people can tell which carby you have there and is it really called a TOKO or is it an OKO and is it really a flat slide or is it a crescent slide? There are lots of different carbies out there

Has anyone tried riding trials on a KT250 using only three of the six clutch springs? I've done this with a couple of TY250 twinshocks and it works out very nicely. Before I try it on my KT, has anyone already tried it?

The crankshaft on the A drives the primary gear with a spline. Later models use a key drive there. The cylinder is different but is interchangeable. The flywheel has a different size external ring but is interchangeable. The ignition stator is the same. The reed cage is the same. I do have the parts books for all the TY250 twinshock models so can look and compare them if there is something particular you want checked

Not a good idea to ride with something attached to the throttle cable

I know you can splice on a new lead because that's what I did with my 348. I didn't try and take the old lead out of the coil though. I spliced at about 25mm from the coil casing. There's nothing wrong with fitting a new aftermarket coil either, but getting one that fits in the available space might be tricky.