feetupfun

from Cota 348 service manual

I would say that the reason it bogs down without the "choke" is because you haven't fully cleaned out the pilot jet circuit

The design changed through the production run as perce says. Brake pedal design, shift lever design, air caps on forks and casing protection loops on the frame. My ride 348 is 51M 10476 motor and frame and has the original style (folding) brake pedal tip, (folding) shift lever tip and no case protectors. Mine does not have the signature on the fibreglass under the seat. It also doesn't have the slotted line along the tank. My memory of the sequence was 76 has the MRR signature, 77 has a fairly plain tank and 78 has a gold/black slotted line along the sides of the tank. I'm thinking that this probably means my ride 348 is 1977 but I'm happy to hear of other opinions.

Degreasing using kero inside and out then hot water with dishwashing detergent then dry it out then quick rinse with acetone and dry it out quickly

Most of the 1970s spanish bike fibreglass tanks that have come into my possession have had extremely poor condition internals with bare glass visible in many areas. You could see areas of thin resin in the dark using a strong torch shone inside the filler hole and can see the exposed glass using a torch and a small mirror. There is no way that I was going to paint a tank in that condition. I have found that after a thorough degrease process then an internal coating of brushing epoxy resin binds perfectly to the old polyester resin and the exposed glass and the epoxy is also highly resistant to the weird stuff they put in petrol nowadays. It adds a couple of hundred grams to the tank and great peace-of-mind to me. The oldest one of mine is an Alpina tank done in the early 2000s and it has had petrol sitting in it since then. The colour of the epoxy inside has gone from light brown to mid brown in that time but otherwise looks unchanged. I've done 5 or 6 old spanish fibreglass tanks so far like this and they are all still going very well and they all have petrol left in them between rides.

If you have a Cota 200 and a 247 frame you are in the perfect position to find your own answer about swapping front ends. I would suggest that you can compare the lengths of both steering tubes and look at how the steering stop from the 200 will work on the 247 frame. If the steering tubes are the same length then it is worth taking the triple clamps out of the 200 and comparing the internal diameters of the steering tubes. Both bikes have leading axle fork bottoms so there probably wont be any issues with clearance between the fork tubes and the fuel tank. If it was me I would much prefer to fit a more reliable motor in the 200. Honda motors are pretty tall. A TY175 motor would be about the right length and height.

If it was me I'd fix the top part and put it back together

I'll second b40rt's comment. I would be checking if the primary drive oil level is going down. It looks suspiciously like smoke from burning transmission oil to me. Two stroke oil-induced smoke usually has more of a blue colour. If the oil level is going down, the prime suspect would be the crank seal on the primary drive side. It should smell wrong too if it is transmission oil.

Maybe clarify what you are asking

A stainless steel automotive welsh plug is another easy way to plug the hole

You can connect the buzzer anywhere between the points and the LT connection on the HT coil. On Yamahas I connect the buzzer at the bullet connector that is near the airbox. The buzzer works best if this connector is disconnected at the time.

After reading and replying to Tillerman6 today, I fitted a new set of All Balls fork seals and they are a different design to what I have seen before. They have a ridge near the bottom of the OD and fitting them required a slightly different technique than previously. They were much harder to keep straight than previous times until they were in the bore. They were no tighter than normal and took little force to move them axially once their whole width was inside the bore. I'm not sure if Tillerman's seals were like this with the ridge near the bottom because mine were a different size (36 x 48) for a Suzuki SP370

No idea why your seal is tight because you haven't said much about what you've done in preparation but here are generic suggestions: Check to see if the bore in the slider is completely round. Clean out the bore with a scotchbrite pad until it is shiny metal all the way to the bottom. Warm up the slider to about 80 degrees C. Put some anti-sieze in the bore. It's normal practice to fit seals in that type of fork with the sliders removed from the tubes. I usually use a 1/2 drive socket that has an OD slightly smaller than the bore and tap it with a small hammer. Plastic coated seals don't usually take much force to get in place

I think it's an Astro (model 90) and you've either misread the first number or someone has altered the number. How about you cover up your secret last number and take a close-up photo and post it up?

I'd like to help but am having trouble understanding the question

The timing will depend on what the advance curve for that igniton looks like and what you are looking for. I fitted an electronic ignition (not the same as yours) because I had just converted my TY175 to 210cc. With the 210cc, the motor response was a bit too fast for me at low RPM. The fixed timing (points ignition) was a compromise between low RPM and high RPM performance. With the electronic ignition with an advance curve, I could get just the right timing at low RPM to get rid of the snappiness and still not compromise the high RPM performance. By the time I was happy, the timing was a bit less advanced at low RPM, maybe 5mm less advanced on the OD of the flywheel compared to standard timing. I would suggest you put yours in the middle of the slot and try it out. If you like experimenting (it sounds like you do) then try different stator plate positions and see which you like the best. A strobe will provide visual feedback for where the timing is, but it will just be moving by the same amount in degrees as you move the stator plate.

Shedworks (UK) for a new fuel tank

With electronic ignition, there is no way to determine the timing without a strobe and the motor running. Yes you have to take the flywheel off to adjust the stator position.

Yes your magnesium MX/YZ/IT backing plate is cool and most importantly the brake torque slot matches the lug on your fork leg. I get my brake shoes relined with oversize thickness linings and then mount the shoes on a backing plate and machine the linings to suit the diameter of the drum they are going into, using a lathe. Most of the brake drums in my trials bike hubs have either been remachined at least once or are worn and need remachining so buying brake shoes with standard linings is not an option. Racetech do make gold valves to suit 34mm DT forks, but they don't list them as such in their on-line catalogue, nor do they list gold valves for 34mm TY250 forks. I bought the gold valves they list for 34mm YZ MX forks and used them on TY250 forks. The Racetech website explains where they sit and how they work. You do need to machine the end of the damper rods and drill extra holes in the damper rods to fit gold valves. Then buy much stiffer fork springs and spend about 20 hours getting the setup working well.

TY twinshock front backing plate vs MX YZ 125 backing plate. Both use 110mm brake shoes

This brake plate came with the mystery wheel. The arm on it in the photos is TY175. I use this backing plate when I'm machining TY twinshock front wheel brake shoes because it doesn't have the arm sticking out like a TY twinshock backing plate does.

Photos of my mystery wheel. In the photos it is holding up the front end of a derelict TY175JC

Yes that is a cool way to help ID Yamaha parts if they have the prefix on them. That list can also be found using google. I was told by a Yamaha dealer that there is a system that records each time someone asks for a Yamaha part that is "no longer available" and once enough people have asked, they start making them again. I suspect that TY175 kickstart levers might be one such part that they now sell. That prefix on your brake shoes doesn't help much with identifying your backing plate though because many Yamahas models use that same pattern of brake shoe.

You didn't actually mention the mode of failure of the wheel bearings on the 4RT. Without knowing why they failed it is hard to know how to make them last longer. In my experience, trials bike wheel bearings last for many years.

That's them yes those three little lugs. The speedo drive casing normally fits between the hub and the fork leg. It's a good design because you can take the wheel and backing plate away from the bike easily without having to undo the speedo cable. The speedo drive and cable can just hang there waiting for reassembly. I've been trying to take some rim stamping photos of my mystery wheel but my phone battery went flat. Photos coming later