feetupfun

The 250 is 10kg heavier than the 175 because the 250 motor is 10kg heavier. The 250 feels light for a 93 kg bike which is a normal weight for a standard 250 twinshock. They didn't sell so many Yamahas by accident. They were designed to appeal to Clubman riders and they still do. The 250 is 16 HP and the 175 is 12 HP. They both pull well and in proportion to their capacity. They both have a ridiculously wide useful RPM range. The 250 is a short wheelbase and the 175 is an extremely short wheelbase. All mods are entirely personal preference. Both are very good to ride stone stock. Many people lengthen the 175 to get a light full-sized bike.

https://www.amazon.com.au/3-5mm-Metric-Right-Thread-0-6mm/dp/B07B4C9TH8 I haven't check the pitch of the Bultaco spokes yet but if they are 0.6mm then I'm thinking of getting some of these and some blank nipples

Heat those nipples with a fine flame and they will fall apart. Any remnants of aluminium can be removed from the spokes by soaking the threaded end in a mild acid

For many years I bought replacement aluminium Bultaco nipples from Bultaco parts people but I think that the remaining stocks of them have been used up by now. It seems a waste of the spokes not to reuse them because the stainless steel Bultaco spokes are/were very nice. For my most recent Bultaco restorations, I gave up looking for aluminium nipples and bought new stainless steel spoke kits, which are quite economical nowadays.

99 is like a square steel funnel with flat filter horizontal at the top. 115/116 has a flat filter in a vertical plane in a fibreglass housing They changed the design to avoid having to remove the tank/seat to service the air filter

No I don't know of a special replacement footpeg mount made to exactly fit your frame. What's wrong with doing weld repairs on the frame anyway? It's not unknown that trials bikes newer than yours have needed weld repairs

Yes repair if you are worried. Only you know your own level of acceptable risk. If it was mine and depending on how much life is left in the rest of the bike I would either fit new peg mounts or let them wear down another few mm. Pre-formed peg mounts are readily available and you could fit them a bit higher than original.

Your idea of a swap sounds sensible. I've bought quite a few trials bike fuel tanks from overseas (UK, USA and France) and I'm not alone in doing that so I guess postage cost is not prohibitive to a motivated person. Your tank would be amongst the best (unrestored, original) of its type I've seen. If your tank was here it would sell quickly for $AU200-$300 (GBP 100-150).

Shane it would probably be good to put an ad for it on the Trials Australia website

I would love to be able to buy that tank from you or swap for one of my 115/116/137/138 tanks, but there is a law preventing sending second hand tanks from the UK to Australia.

The photo I posted is a 115 and the cylinder looks different to your 116 because it is a 250 and that is how 250 cylinders looked until around 1974. After they changed the 250 cylinder finning design to a more open spacing, the 250 then looked very similar to the 325/350 cylinder. The common name for motor in the photo I posted is round barrel because viewed from above, the fins form a circle. The round barrel 250 has poor heat rejection capabilities because the fins are too closely spaced. Bultaco realised it was a problem and when the 325 came out it was made with wider spaced fins that form a square when viewed from above. The 250 was later changed to a similar finning design to the 325. Other than the motor capacity and the colour of the stripe on the tank, the 115 and 116 are the same.

The 85/99 tank you have is more valuable than a 115/116 tank

This what your Alpina tank shape should be to fit your frame. This is a 115 which is the the 250 version. The 115 and 116 have the same shape tank. The 250 has a silver stripe and the 350 has a yellow stripe

That looks like a tank for Alpina models 85 and 99. That tank is made for the Alpina frames that don't have the frame element that runs upwards and forwards from the swingarm pivot

I'm in Australia, and every 1970s Spanish fibreglass tank I've lined looks the way you have described it beforehand or worse. It doesn't matter if it leaks or not before you do the job

They are all rough inside and petrol-soaked to start with. The prep work needed for relining includes very thorough degreasing. There's an Indian company making replica aluminium Alpina tanks but they don't make the 115/116 type (yet). They do make Alpina 85/99 and Alpina 212/213 tanks, neither of which look right or fit your frame. Second hand 115/116 tanks are available if yours is unable to be lined. I have a couple but am a long way from Scotland. New replica seats and clubfoot exhausts are available. Good second hand seats and clubfoot exhausts are very rarely seen for sale.

Yes have a look at Shedworks (UK) and In Motion (UK) websites and you'll see tanks they sell like this. Some people make their own. It's not hard because it doesn't have to be pretty. There are different brands and types of resin liner but the one I use is a low viscosity (brushing) epoxy resin from a marine supplier. Yes it is applied by moving the tank around with the liquid flowing to cover all inner surfaces and the excess runs back out. It doesn't swish though. It's much slower than that, more like how warm honey flows. The preparation of the inside of the tank is extremely important for a successful job. If you want to buy a kit, a popular brand seems to be Caswells

Being yours Shane it sure has provenance and there are people who have a thing about them so I have no doubt it will sell easily. I sold my well-used but fully functional 1993 TYZ locally in Gladstone for $2500.

That might work if you work the rear brake against the motor in top gear with the clutch lever pulled in, but it sounds like a fairly hazardous thing to do. Clutch RPM is not a factor in whether it will free up or not.

If you want to keep riding without pulling the clutch apart and servicing it, you will find that riding around in a high gear with the lever pulled in will free it up pretty fast. The higher the gear, the greater the torque that is transmitted by the clutch for the same torque at the rear wheel. Motor stopped, top gear, clutch lever in, your weight on the bike and push backwards with your legs is another gentle way to free it up.

Yes it is a normal thing to use a metal tank under the top part of the old fibreglass tank. Another option for old Spanish fibreglass fuel tanks is to line them with fuel resistant resin.

It is good to know that you are getting some voltage at the fan because it means that the stator coil is working. Yes the DC voltage at the fan is too low. I don't get what you're saying about the capacitor except that you think it s OK.

Yes Maybe What did you find when you measured the voltage at the fan?

https://www.ebay.com.au/itm/MICHELIN-TRIAL-X-LIGHT-FRONT-IRC-REAR-TUBED-TYRE-SET-NEW-BRAND-NEW-STOCK/233866345145?hash=item3673853ab9:g:-6sAAOSwDEtaAdDy&frcectupt=true

Check what is going on with a multi-meter. The most common reason for the fan not running on a trials bike is the thermostatic switch not making/closing.