feetupfun

I didn't say to buy a trials bike. That was someone else. The TY250 parts book does show two springs but they really only came with one main fork spring. I'll have a look at the parts book tonight and that will remind me of what you are looking at. Many people have said the same thing as you previously about the parts book. Yes TY250 fork springs for 34mm Kayaba forks will fit in 34mm Kayaba MX YZ forks. You would need to make custom length preload spacers. Trivia fact No 1 - you can fit Race Tech Gold Valves designed for MX YZ DT 34mm forks in 34mm TY250 forks. You say your forks are similar but not identical to 1975 YZ250. What do you see that is different? Trivia fact No 2 - if you have a look at photos of some of the early prototype bikes that Mick Andrews rode while developing the TY250 you will see what looks like your front hub and fork sliders in use - straight out of the Yamaha parts bin.

You could use a plank as a balance beam, put the motor at one end and add mass (water in a bucket that has litres marked on it) to the other end. Measure the distances from the fulcrum and multiply the distances by their mass to give you the mass of the motor. Motor mass x distance to fulcrum = mass of water x distance to fulcrum Motor mass = mass of water x distance from bucket to fulcrum / distance from motor to fulcrum

From what I've read, he's got a TY250 twinshock that has the trail riding kit that was available from Yamaha (and popular in the USA) when they were new. It sounds like someone has fitted a YZ 250/360 or MX 250/360 front end from the mid 1970s to the TY.

The writing on your MX YZ forks is not TYB, it's KYB, which is the company that made forks for Yamaha at the time. KYB is the trademark for Kayaba. Yes you will need to have the fork tubes sticking out the top for it to steer properly. Yes it is best to leave the springs out when testing fork travel. Those Falcon shocks are a good length if you are not lowering the footpegs. Original shock length was 325mm. The ground clearance with those Falcon shocks will be fine. Set the sag with you aboard to 40-50mm. If you want more ground clearance you can fit longer shocks but with longer shocks, standard position footpegs will be too high for the bike to handle well with you standing up. 15WT oil in MX YZ forks may be too heavy damping for a trials bike but try it first. It is easy to replace. The MX YZ springs will probably be too stiff for trials riding but try it first and you can fit TY springs later if you need to. The top hat washers should sit on the top ends of the fork springs. Yamaha use that sort of washer so that the cylindrical preload spacer that usually fits above it can be made very thin-walled yet not slip past the end of the spring.

Your triple clamps are TY Yamaha. Your fork sliders are MX or YZ Yamaha and your brake backing plate is MX or YZ Yamaha. The lines on the fork tubes are there as a reference for where to clamp them on the bike that they originally came from. If they are longer tubes than TY250A then they are not TY250B, because all the TY250 twinshocks have the same length fork tubes. I would expect that the fork tubes are also off a MX or YZ Yamaha. To maintain the standard TY steering geometry you should set the tubes so that the axle is in the same position as it would be with TY forks. If the travel of your forks is longer than TY forks you may need to fit travel limiting spacers to the damper rods, to avoid the mudguard or tyre hitting the lower triple clamp.

A very hot exhaust header and poor running can be caused by the ignition timing being set too late

smells nice too

From what you have written it sounds like you have non-standard forks, so to know how high you can have the mudguard above the tyre, you will need to test where the tyre OD is with the forks fully compressed. Standard TY250 forks don't have much room between the tyre and the lower triple clamp and yours with different forks might have even less.

I've not seen a front wheel rim tape glued on. Do you know why it had been glued?

On my SM TY175 pegs, the holes for the pivot pin elongated. I do weigh 95 kg though. I welded on some thick washers and they have been OK since.

reminds me of: Hey. You. Get offa my cloud

If spring steel yields over a long time period when loaded below it's yield stress limit, then yes. Bear in mind that clutch springs only carry slightly more load when the lever is in than when it is out, so it probably doesn't make much difference to how long the springs last storing the bike that way.

Some (not many) MK4 Matador components are shared with Alpina and Frontera. I would say they are no more or less valuable than any other early 1970s Bultaco.

Depending on the price of a new basket, it may be cheaper to pay someone to machine the finger edges flat with a milling machine. That would be about 30 minutes work on a milling machine

Yes I've done it but it was a few years ago so the photos will be a fair way back in the forum. It was the first time mine had been apart. One of the boxes had metal wool packing and the other was mineral fibre. Can't remember which was which. I used mineral fibre in each and made new perforated tubes for one of them. Mine didn't run any better after the repack but was lighter and quieter. I notice that later model Montesa trials bikes of Spanish origin had a much longer header pipe than the 348 which may mean that having the front section packed at the right density where it is in contact with the perforated tubes could be important.

YZ125C and YZ125X had this cover

I just bought a bike that had been sitting for 15 years straight with the clutch lever held in with cable ties because the owner didn't like it to stick. The clutch works perfectly

If they have falcon springs, the rate is usually engraved on one end of each springs, on the flat bit. They usually have just the first digit ie 5 for 50lb, although I have some that have the full number 50 for 50 lb. If there is nothing engraved you can work out the rate using a coil spring calculator of which there are many available free on the internet. Falcon springs are not colour or finish coded. Standard used to be chromed and now standard is powder coated black.

I'm not sure of your question. It shouldn't matter how much free play the arm has. Are you saying the cable inner is too long?

http://www.southwestmontesa.com/production.html This list says 250 Enduro and the first 3853 of them were made in 1974 so your number looks like 1974

Two stroke trials bikes are easier than two stroke MX bikes because they don't have power valves

Yes Maybe Maybe Hard to tell from your description what is causing the problem. Could be lots of things

OK first i want to clarify that this forum string is about TY175 footrests, which attach to the frame completely differently to TY250 footpegs. It sounds like you are asking here about TY250 footpegs, As for what a bike does when you blip the throttle, it is pretty much impossible to communicate bike response like that on a forum, in words. I can say that if you are sitting down and riding along flat ground in fourth gear, a combination of weight transfer, throttle position and clutch dumping will lift the front wheel high enough to get to the balance point. If you want to do a balance point wheelie in fifth gear on the flat you will need to be standing on the pegs to get enough weight transfer. They are about 16 horsepower. So much of what a bike does is determined by what the rider does with their body, that your question needs to be a lot more specific to be able to be answered. Keeping the front on the ground or floating around off the ground is something the rider controls, no matter where the footpegs are. I have no idea how the tyres I use are made. I remember that radial ply rears (AVON) came out in the 1970s and competition tyres have continued to improve since then. I run IRC tube type and Michelin X11 tubeless type rears with a tube on my twinshock trials bikes and they work way better than 1970s design tyres.

I've previously bought a new threaded insert from Keith Lynas in the US made from aluminium and then locally had the hole in the cylinder machined out and the insert welded in place.

Zinc-rich-primer (used for painting welds on galvanised structural steel) usually has a matt finish that is pretty much impossible to keep clean. I paint my frames with automotive lacquer for the same reason you mentioned - it is very easy to touch up the inevitable scratches, but it looks good, unlike the zinc spray paint