feetupfun

I suspect that oni nou's post was intended to be interpreted as being sarcastic humour

bigshineybike reminded me to mention that the 349 and many other spanish bikes of the time use 0.5 mm thick centre gasket, which is not a standard size here, but is available. The thickness of the centre gasket is important for things like the side play in the shift drum

A friend of mine did have an arrangement with a bikers cafe where he would display his old trials bikes in rotation in suitably benign conditions.

This is what I made to remove Cota 348 primary drive pinions. It worked a treat. The 247 drive gear is very similar to the 348.

As long as the mixture is right there is no harm from poor combustion happening by having the air screw all the way in. However, if the pilot circuit is working normally and the air screw has to be all the way in to get the mixture right, then there has to be unfiltered air going into your engine somewhere which will cause damage. Have you checked the oil injection port for air leakage? On one of my bikes I had used a piece of plastic tubing to seal off the oil port and the tubing had swollen over time and had started to let air in. When you look at the LH crank seal, the evidence for a leaking seal may be very small. Even if there is no oil witness there, it can still be leaking. Sometimes that crank seal will seal in one direction but not the other, so air can go in but no fuel/air mix comes out, so no witness. I've just found exactly that failure mode on my KT250 LH flywheel side crank seal. One difference between a problem with the pilot circuit and a problem with air ingress is often that with air ingress via a crank seal or the centre joint of the casings, the degree of the problem will be quite variable, but if it is the pilot circuit that is the problem then the symptoms will be fairly consistent.

I'm thinking that because bsw posted in the Yamaha forum, maybe the Miller tank/seat unit is from a Yamaha in which case yes one of the Shedworks fibreglass tanks would be a suitable way to go.

I usually just tell the person behind the counter what it's for and they sell me an o ring made of the right stuff

Wiseco pistons have a higher coefficient of thermal expansion than Wossner pistons, so need more piston/bore clearance (when measured at room temperature) than a Wossner. In theory the clearance is the same once the Wiseco is up to operating temperature. Running in a rebore is getting the bore and rings to bed in against each other so the contact surfaces can form a low-friction gas seal. While the running-in is happening, there is a lot of extra heat being generated by the friction of the rings against the fresh bore which can (amongst other things) cause the piston to get hotter than it should, which can cause the piston to get too big which can cause it to nip up.

Could be, but not enough info to know for sure. How quickly is the throttle being opened? What happens when you try it with the starting circuit in service? It is doing the same thing hot and cold?

The original kickstart shaft breaks. Replacements can be custom made but are expensive. Original plastic fuel tanks that haven't failed yet are a rarity. The last model 350 is lots lighter than the first model and is good to ride (similar feeling to an SWM TL280)

Some friends had practiced trials for 20+ years on their couple of acres on two-strokes (twinshocks and moderns). The closest neighbouring house is about 150 metres from their riding area. The neighbour had never said anything to them about their riding there until one day when a friend came and practiced with them on his 4RT and the neighbour came over and complained about the noise.

Single front downtube frames have been a rarity for a long time now. The only one that springs to mind is the Scorpa with the TTR125 motor and the Scorpa looks quite different around the headstock, so I'm betting on the main frame being either a scratch-build custom job or heavily modified Bultaco

I saw a question in there " Would an XR/XL/ATC 200/250 motor of earlier 80's vintage be a bolt up swap?"

An interesting change was made by Beta during the 2000s in their two stroke Rev 3 range. They wanted to reduce the overall mass of the bike and one change they did was to change the shape of the crank wheels. They made them thinner and increased their diameter. The mass moment of inertia of the crank wheels remained the same but the mass of the crank wheels was reduced.

Are you wondering why, if it works so well on your bike, why having twin rear sprockets is not more commonly seen?

I don't remember any here in Australia back in the day

I've also run a TY (and a Bultaco) using a lighting coil as the ignition stator coil and it went fine. Yes the voltage generated will be different because there are different number of coil windings, but it is obviously close enough to work well enough.

If you become a site supporter you can post as many photos as you want. When you are talking about the height of the pegs relative to the axles, are you talking about bike laden or unladen?

I'd say in the case of those OZO shocks, it's just the result of poor translation into english when they wrote the advertising blurb. Remember "foam cell" motorbike shocks? I wonder if anyone still makes motorbike shocks using foam blocks instead of bladder/diaphragm or floating piston. I remember that Kayaba gas (twin and mono) shocks from the mid to late 1970s with floating pistons had "de-carbon" written on them, which I think was a copyright-protected term. One thing that I'm interested to learn about is a phenomenon happening inside standard Falcon trials shocks. They have no separation between gas and oil. They work noiselessly with gas pressure inside, but if you let the pressure out, you can hear what sounds like gas bubbles going through the damping mechanism when they are worked. How can adding gas pressure make the sound go away?

In Motion know their stuff. Those old-style Betors are perfect for a show bike from that era.

I use the basic modern gas Betors on my 350 Alpina and find them fantastic for trail riding, but the compression damping is a bit heavy for trials riding. What do you mean by "effective range is minimal"?

I wish I'd thought of this Greg. I just went through the clamp, tack, straighten, tack, weld procedure on my KT250

I think he or his mate was going to have a fiddle with the damping

Interesting to see that they use an anti-topping spring. The rest looks fairly normal to me. How smooth is the section of bore that the floating piston O-rings run on?

I can confirm that there were more than 2649 B models (1975 525 model) made (because I own 525 - 003013) and there would have been way more than 2543 C models (1976 525 model) made. I suspect that those numbers you have quoted may have been the serial numbers for bikes sent to one region of the world, rather than world-wide totals