feetupfun

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

With any tyre the rubber goes hard with age. The tyre bead has probably taken on the bead seat profile of the old GasGas rim as it aged. The newer rim may have a slightly different bead seat profile and the tyre bead rubber is no longer flexible enough to deform to the shape of the newer bead seat. If the tyre is the same age as the 2005 rim, it is an extremely old tyre. There are liquids designed to soften the rubber on go-kart tyres that might soften your beads enough to get it to seat and stay seated. I've got my doubts about WD40 softening rubber. I've been using WD40 for years as a mounting lube but have not noticed any softening of the rubber. Another technique would be to heat the beads and rim up just before you pop the tyre onto the bead seats and then leave the whole thing cool down with the seating pressure still inside. Yes, high temperature contact adhesive would work but may make tyre removal interesting.

I just bought new Falcon bushes for exactly that reason. OSSA MAR and KT250 both have large diameter upper mounting pins.

Welcome Steve. You certainly add to the enjoyable atmosphere at the trials you come to

Thanks woody

If the motor, carby and exhaust is standard then the standard air box is fine. If you increase the engine capacity or improve the breathing then you may benefit from a freer breathing airbox

The KT bars were the highest trials bars I could find at the time and are slightly higher rise than modern 6" rise Renthals. Since then I have had a few sets of alloy handlebars custom made to replicate original 1970s trials bars. People sometimes comment that they look too high. Luckily there are plenty of historical photos around. I'm 5' 10" with average length legs and arms for that height and if I was going to use modern 6" Renthals on my OSSA I would space the mounts about 25mm higher than standard as a starting point. I will be interested to see how the footpeg lowering is accomplished on your friend's OSSA.

and what is the brake drum ID?

I used flat plate spacers under my standard MAR bar clamps to raise the standard bar mounts about 20mm and bought longer 7mm screws. The bars on it are replica KT250 bars and the footpegs are standard pegs in the standard location. I considered lowering the pegs instead of raising the bars but lowering the pegs on an MAR is problematic and I didn't want to have to repaint the frame (it is powder coated). I find it rides a treat with this setup so am not motivated to make changes.