feetupfun

Tilllerman I think I need to clarify: 12/55 is even better than 13/53 for trail riding, because it brings 3rd 4th and 5th gear even closer together than 13/53. For some reason I thought you were thinking about getting a 14T front. The reason I said to take off in 3rd gear is because you said you were not liking taking off in 1st gear. A TY250 with 12/55 gearing can start off easily in any gear except 5th. When I said that you should use the TY250 broad power to your advantage I meant that when riding single track you should avoid rowing up and down through the gears. I've just seen the photos of your bike and that rear tyre will be making it much harder to ride rocky and loose trails than if you had a competition trials tyre on it with 4 psi.

RM is one of the prefixes Bultaco used on engine numbers. The R is the capacity and the M is for motor. The A at the end means it is from a model 198A not from a model 198

Maybe the linkage broke? It does look fairly odd with those shocks there

When you say "There is a few bits missing as you can see from the picture", I have looked but can't see any missing parts so what parts are missing?

Lots of different dogleg lever blades fit TY250 mounts and cables. One of my favourite dogleg levers on old Japanese trials bikes is (genuine) Suzuki RM80X. They are very malleable. You can also use mounts that have a split clamp which makes it possible to change out a broken mount without removing/replacing the grips.

13-53 is good for trail riding and only use 3rd 4th and 5th. When you take off, use 3rd gear. 1st and 2nd are rarely used for anything except trials sections. 14-53 puts 3rd 4th and 5th too far apart for trail riding. Leave it in one gear and use the broad power range. Most of my flowing single track is done in 4th gear and for really tight corners (like when you actually have to turn the bars) I fan the clutch for a moment on exit. Steep and rocky trails use 3rd gear. Extreme steep and rocky trail use 2nd gear. Modifying the engine is a waste of money for what you are doing with the bike. It is an excellent motor completely standard. Logs are successfully crossed using rider technique. Think about MTB (bicycle riders) jumping a log. They don't have boyesen reeds and their motor is only about 0.25 HP but they can fly over logs at speed. Riding across logs is a valuable trials technique that there are endless training videos about and success comes with knowing the techniques and practicing them. Barkbusters are good for avoiding catching lever tips on vegetation but even the lightest versions affect the steering when doing competition trials riding. If you are only trail riding they are fine.

That steel band is a tight fit on there. Yes it can be taken off and put back on but one would need to take great care in the process to avoid damaging the magnets or the flywheel cup. Using a purpose-designed flywheel holder and pushing/pulling tool would remove most of the risk. I was so cautious when I removed one of them I cut it through with a hacksaw to release it and minimise the risk of damaging the flywheel. I lend that flywheel to people who are thinking about taking their weight band off so they can try their bike that way first. None of them have removed their own band after trying that flywheel out first, but some have lightened their BCDE models weight band. Note that the A model already has a light weight band, much lighter than the BCDE models. In my experience, trail riding an A model is brilliant fun and you can ride the things very fast in single track conditions even with the standard 16 HP engine with standard flywheel, due to their broad power, light weight and excellent handling. 95% of riding over expected logs and unexpected logs is rider weight transfer. The trick with going fast with one of these bikes is to stay on the pegs and stay in one gear and use the broad power. Low gearing gets 3rd 4th and 5th gears close together and these are the gears you use trail riding. Road gearing makes for big gaps between those gears.

Some people cut the TY250 LHS cover back to expose the sprocket to allow better mud clearing. Where I live it is compulsory to guard the front sprocket in competition use and we don't get much mud so it's very rare to see shortened covers here. Never heard of it being done to help prevent chain problems following a chain failure and I can't see how it would help with that. On the TY175 in the 1970s, it was common to cut the LHS cover in two so you could change the front sprocket without taking the flywheel cover off. The rear half of the cover was still held in place by two screws so you still had the sprocket guarded. People did this because TY175s were often used for both trials riding and for trail riding and on the road so owners were frequently changing out the front sprocket. I was one of those riders in the 1970s and used a 13T for trials and a 15T for trail riding and a 16T for road riding. Here's a photo of a TY250 with the later model LH cover shortened found after about 20 seconds of searching google images.

The standard sprocket retaining nut is 26mm AF. There is no locknut.

If it goes good before it dies during sustained high power then it's not float height. From what you have said it sounds like the fuel level goes down with sustained high power. The usual causes for this (apart from low fuel level in the tank which you have already tested for) are: Restrictive fuel tap. I can see in your photo that you have the original type fuel tap and they are notorious for having a poor flow rate. Blocked strainer on the fuel tap inlet. Blocked fuel strainer inside the banjo fitting on the carby. Blocked in-line fuel strainer. Blocked tank vent. To answer your question about the float height yes you can adjust the fuel height by using different thickness bowl gaskets. If I have misinterpreted what you said and you are actually saying that it dies when the front of the bike is above the back of the bike then that is a different kettle of fish and you can test for this by lifting the front of the bike up with the motor running and see if it makes a difference. There is a weakness with concentric bowl AMAL carbys in that if the front of the bike goes a lot lower than the back of the bike as in dropping down something extremely steep, the idle speed can drop off sharply. That weakness is one reason I use a modern carby on my model 49.

And it's known as a Beta Techno. The Techno series went from 1994 to 1999.

Mine came from Ivan Cirre in Spain. You will find their website using Google. It was the only place I could find one when I was looking about 10 years ago. They are probably more easily sourced nowadays. In Motion has them on their webpage but it is saying out of stock just now. A friend of mine made one that works well too. It wouldn't be hard

I run an aftermarket (modern) replica trapezoid end muffler on my model 49 and it does not take anything away except noise. I'm fairly sure mine is different inside to the genuine Bultaco trapezoid end muffler

http://www.southwestmontesa.com/gallery.html

http://www.southwestmontesa.com/modelyear.html

Plenty of people have bored the later (square barrel) (238cc) cylinders out to fit a 280 Gas Gas piston but the model 80 is a different design cylinder to the later design cylinders

Fairly rare nowadays to see a Hodaka being ridden. After looking at trials bikes for so long, the footpegs look to be a long way forwards. Apart from the low gearing, how was it to ride?

Not a stupid question. Mineral turpentine is what I use, followed by a warm solution of dish-washing liquid then cold water rinse then wrapped in absorbent fabric and squeezed then allowed to fully dry out by evaporation

The standard tank on them was plastic and it did breathe vapour through the walls which can cause paint and stickers to bubble but is otherwise fine to use. All plastic tanks breathe petrol vapour. If your tank really is GRP and I see you are in the UK so it is at risk of being dissolved by your fuel but it can be lined with epoxy resin to make it fuel proof for your fuel. A photo would help determine what it is made from

There was an era when the 290 Sherco was only suitable for top level riders and there seemed to be quite a few for sale cheap second/third/fourth hand that had been bought in error by people thinking they would be good to learn trials riding on. There was also an era around then when Shercos didn't have much steering lock compared with other brands so you needed to be able to hop the front where something like a Beta would turn much tighter with both wheels on the ground.

Yours has the later arrangement for the brake pedal pivot. The early arrangement had the pivot location to the rear of the frame upright. Is your engine number also somewhere around 1787? Your rear wheel looks like the early type hub (shared with model 10 and model 27) Here are photos of my series 1 model 49 (49-00100) showing the early brake pedal pivot location (and brake pedal) and early type rear hub.

All the 250 twinshock TY250s they sold in Australia (and the USA) were competition models with the speedo attached to the left fork slider. In Japan and some European markets they sold twinshock TY250s with full road equipment which may have had a bigger speedo mounted up in the normal motorbike position. I've seen TYs in Australia with both MPH and KM/H speedos on the fork leg. I don't remember which models had which speed unit scale. Maybe start looking soon because nice ones are rare/expensive

Yes looks like Godden numbering 81 = 1981 11 = November 01 B = no idea. Mine has three numbers next (106) As for knowing if it's a 250/320 Godden frame or not, the Godden frame is very different in design to the Yamaha-based 250/320 Majesty frame Yamaha frame numbering is very different too. For the Yam framed Majestys, they used D and E model frames with numbering 493 - xxxxxxx

Top shock mount location moved down and forwards to where yours are during model 49. Brake pedal design changed during model 49. Can't see yours. Frame tubes under engine went from single middle tube to a smaller tube each side during model 49. Outer engine casings design changed to your type during model 49. This co-incided with the frame tube change under the engine. This change was somewhere around number 2650. I don't have the book with me at the moment with the number in it to refer to. Rear hub changed during model 49. Can't see yours well enough to say which one yours is. Your lack of frame tubes under the engine is non-standard but is a common mod. The book " Historia de la Sherpa T" by Francois Stauffacher is a good reference book for Sherpa T identification

Thanks for sharing this. Very interesting.