feetupfun

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.

Of course there are a lot of things that could be causing your issue but the usual (simple) thing that causes those symptoms is a blocked pilot jet or blocked pilot jet passage (in the carby). The fuel hole in the pilot jet is a tiny thing and blocks very easily. If you are confident enough, you can take the pilot jet out and clean its hole. When you can hold it up to a light and see through it clearly you will know you have cleaned it out.

From my experience those pressed steel caps are only fitted to the outsides of the crankwheels so they are not actually "stuffers" as such because they don't reduce the volume of the crankcase. Did yours have them on the inside ends of the holes as well as the outside ends? If you want there is no law against using stuffers in a TY250 so yes you can use cork or balsa stuffers. The usual sealant however is epoxy resin rather than varnish. I find the standard motor runs amazingly well without stuffers and some people even space the reed cage outwards to increase the crankcase volume so it may not be a good move to fit stuffers if you are not wanting to go out on a limb. Those steel caps may be there to provide some sort of streamlining of the crankshaft to reduce aerodynamic drag at high RPM. I would say that their presence or lack of presence is not something important for performance. Their presence is definitely a liability for the risk they pose should they come loose

MITAS are as bad as MT43

Sounds like they changed the cylinder casting and fork sliders at some point after 006798. There was also a change to a plastic base for the seat pad instead of steel at some point

Nigel this is what the Peter Paice TY250 frame sidecar looks like. If you are seeking current design philosophy for trials sidecars rather than what people used in the 1970s, Justin Gough would be a good local to talk to

From memory there is a set of dimensioned basic drawings in the MA M.O.M.S that show the size requirements for competition trials sidecars in Australia. Also pretty sure that Ron Chadwick (Brisbane) has a sidecar on a TY250 twinshock that you could probably arrange to measure up. Another one for a TY250 twinshock (further away though) is owned by Peter Paice (Newcastle NSW). Peter's TY250 that the sidecar fits is currently at my place in Gladstone so if it helps I could send photos of the attachment points on the bike.

That plastic bit should be inside the tube behind the snap ring. The right side tube in your photo is the correct setup

My OSSA also has the top mount larger than the bottom and it doesn't have an old sleeve still there