feetupfun

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

Wasn't there another forum string about this a few weeks ago? Maybe have a look back because your Beta 4T symptoms sound a lot like the other person's. I've just added a link to the string. It started in 2012 but was active again a few weeks ago

Learn how to check the timing. You don't need to accurately measure piston position to check it is in the ballpark. Here's my suggestion: Take the plug out. Take the flywheel cover off. Find top dead centre using a clean object inserted through the plug hole. Make a mark on the flywheel rim in line with one of the holes that the flywheel cover screws go into, with the piston at TDC. Measure around the rim of the flywheel anticlockwise 22mm and make another mark on the rim. Get a torch and look at the points. Find the flywheel position where the points start to open when rotating the flywheel anti clockwise. It should be close to where your second flywheel rim mark is aligned with the screw hole you chose. If the points open within a few mm either side of your second flywheel rim mark then your problem is not your ignition timing.

If you are talking standard bikes, standard TLRs are about 10 years worth of bike development better than standard TLs. Where I ride, twinshock class trials machinery is pretty much carte blanche. With enough effort and know how, you can make a TL125 go just as well as a TLR, and people do. The performance limitations in our twinshock class come from having to have drum brakes, twinshock rear end and a motor that originally came from a twinshock motorbike.

no idea. It's a pain to do it too. I can only remember the number from one of my twinshocks. The rest I have to go looking with a torch. Maybe I should make a list. A friend of mine who also rides multiple bikes confessed last weekend that he just makes up the numbers each time "because no-one ever checks them anyway"

Sorry for not being Guy, but all over the world people remove three of the clutch springs on TY250 twinshocks to lighten the action

Frame and engine numbers on entry forms for trials competitions has been standard practice in Australia for as long as I can remember, but I don't think anything is done with the numbers

The body of the silencer is the same (250 vs 175) but the inlet pipes are different length and shape

My WES end mufflers on TYs are quieter than stock too

Modern internals vs modern forks makes no difference, but fork visuals are important to me. As for the motor, there are potentially important advantages from using a later motor, such as less weight, less width and less length

The last video looks like how a standard Ty250BCDE in good condition responds. The standard motor has a strong flywheel effect that most people didin't like when they were new and the same sentiment applies even more nowadays with grippy tyres and good rear suspension. Lightening the flywheel is a very common mod to these engines. Another beneficial mod to make them more snappy is to fit a good modern ignition.

How about a photo of what you are talking about

Make or find a puller that doesn't damage the gear teeth. The usual two or three arm puller will likely not be able to pull hard enough and will damage the teeth. A suitable puller will pull against the back side of the gear without touching the teeth and it will pull on the whole surface, to spread the load better. I made a tubular puller that is in two halves. There are discussion threads on this forum that cover this job in detail. I can do photos again if the thread has disappeared.