feetupfun

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.

Metris is called Vito here and they are a popular, well-regarded vehicle with lots of variants. The commercial van versions are commonly seen at trials events. Larger (sprinter) MB vans are also popular for bike carrying. No idea how they compare to the Chevy Express but the Vito is definitely better than the other european vans of that size and better than the Toyota. I drive a Hyundai H1 (iLoad) van and prefer it over a Vito.

What do you mean, "a reference"? My only memory of such things is magazine tests from the 1970s that measured the weights at each end without a rider, which is a fairly meaningless set of numbers on its own. The weight on each end with rider aboard is different for a given bike for riders of different weights. I'm interested in what you are seeking

Those percentages are not swingarm length/wheelbase. They are footpeg to rear axle/wheelbase

Sounds like the pilot jet or pilot jet passage may be restricted/blocked