feetupfun

I think Alan's bike is a TY250A and I know from back to back testing of my bikes, that standard TY250A motor performance is very different to the B and later models. The weight band on the A model is a bit narrower than the band on the TY250B and later models, but if you put a B or later weight band on the A model, it actually makes riding the bike harder, not easier. I know because I tried it. The problem with the A model comes from the internal differences between the A model and later models. I suspect it is the port timing but my early TY250A motor has never had the barrell off so I haven't been able to compare it with a later model barrell. The effect I'm talking about is that at extreme low RPM, the A model motor responds to throttle input quite weakly, but at a bit higher RPM the throttle response is fine. This makes the A model a bit exciting in tight riding (when the RPM moves through the transition in either direction). Alan the guys at B&J Racing in Tennessee have a handle on this and have some sort of fix available. Another alternative is to find a B or later barrell for your bike.

http://www.yamaha-majesty.com/product_info...products_id=145 http://www.yamaha-majesty.com/product_info...products_id=143

The degree of restriction that the airbox creates, whether from the cross sectional area of the airbox entry, or from the type/thickness/area of filter media will also affect the jetting. Depending on whether your TY250 Mikuni carby is from a B model (two big round holes in the side of the airbox), or from a C or D model (air entry is via a baffled slot in the airbox lid), the ideal size of the air entry to the airbox will be different. The standard jetting in the two different TY250 carbies is quite different.

http://www.trials.com.au/phpBB3/viewtopic....f=16&t=4587

Yes thats it. The "check valve" for compression damping is a round thin steel shim designed to provide rate-sensitive compression damping by flexing out of the way of the oil.

Yes Tony the standard carby on the TY250 uses an external air supply to the emulsion tube. I think you tricked a few people saying it is a standard VM26 carby. It is a Yamaha VM26 Mikuni which is quite different to the off-the-shelf VM26 Mikuni. It is a bit of a weak point for the bike because the emulsion tube requires frequent cleaning out due to dust ingress up the hose. Yes the end of the hose needs to be at atmospheric pressure. It has nothing to do with the pilot/idle circuit.

If you shorten the spring, there will not be enough travel left in it. There is barely enough intercoil space already for the fork travel. I find that both the rebound and compression damping is too light even with 20wt fork oil. I weigh about the same as you. When you push the front down and up by hand, the forks sound like there is not enough oil in them (ie they snore) even if you fill them up to 125mm below the top when bottomed with the springs out, which is a fair bit more oil than the specs list. Heavier springs are available, but while they resist bottoming better, they exacerbate the lack of rebound damping amongst rocks. They are good except for the effect when riding rocks. I want to try cartridge emulators, but will wait till I need to change the fork seals next, as the forks are tolerable the way they are. YSS make the right size emulators for the TY250 forks (emulators intended for YZ250/360 from the 1970s)

Here you go Jaan http://www.francetrialclassic.com:80/fr/pr...348-et-349.html

No one twinshock trials bike is best for everything/everybody, but many people have a favourite.

How can anyone riding a modern bike sitting down and cover the brake pedal at the same time? Twinshocks are fine, but on moderns my foot won't bend up enough if I'm sitting.

The model prefix for at least one model Yamaha TY125 is 539. The TY175 and TY125 are based on the same basic bottom end so there shouldn't be a problem if someone has made it into a 175.

Yamaha engine number prefix 539 is TY125 so yes no problems

The WES aftermarket muffler is very quiet and vary light. We have a road-registerable model TY175 here that has a quiet muffler. It is quite a bit bigger than the common TY175 cylindrical muffler but blissfully quiet. Not sure if you got that model or similar there. The muffler I'm talking about is the same as the TY125 muffler as they were sold in Germany, France and the Netherlands (and probably lots of other places). The bike we have here is called TY175JC and it came with a small snorkel on the airbox inlet and rubber fin dampers, which reduced the noise even further. Yes I dislike the noise from standard TY175 exhausts too.

I think he was having a dig at Gas Gas

Putting a thread on the OD of the flywheel is certainly a novel concept, but would not have the effect you desire. It would increase the aerodynamic drag of the flywheel which would reduce the power output of the motor, and would increase the amount of agitation of any solid material that is trapped inside. Reducing the mass of the flywheel will reduce the gyroscopic forces generated by the flywheel when the bike is turned or leaned over. The reduction in flywheel inertia will be much more noticable to the rider.

Neo the AFAM bars come from my local motorbike shop (Suzuki, Yamaha, KTM and MV Augusta) I'll post a photo showing what they look like (Wendy riding)

Sounds like the rubber intake connector has developed a leak

The coolant should be getting controlled to about 100 degrees C by the fan stopping and starting. If the fan runs all the time, the motor will run too cold. If you can hold your bare hand on the outside of the barrel for more tham 10 seconds, the barrel is 50 degrees or cooler which is way too cold for a motor to be happy. It might perform OK, but it will wear out much faster than it would if running at a constant temperature.

Both types of 348 brake pedal work well for me. Have a look at some photos of 348s and you'll see the other pedal type. The kickstart is s bit non-ergonomic in location (high and well forwards) and combined with the bigger motors (348 and 349) it can take a lot out of the rider through the course of a trial - best if you can keep the motor running - but not easy if you live somewhere hot because the motor can overheat if left idling. I find that it isn't too much effort to start if you ease it over compression before giving the starting kick. I think it would be pretty hard for a youngster to start. The 247 has the same kickstart arrangement but is easy to kickstart due to the smaller displacement motor.

Without knowing what your lever is like that is a pretty hard question to answer. Some 348s have a folding tip lever that would be pretty hard to use if the tip was missing. Have you lowered the footpegs? Both types of standard 348 brake pedal work pretty well with the standard footpeg location.

Neo I hope I've beaten Maree to this one. I couldn't resist asking have you ever fitted Bach Busters to your Handel Bars? AFAM bars are quite crash resistant as far as 7/8" bars go and nice ergos too. David Lahey

Aussie Bultaco fanatic Paul Paterson was given a very nice birthday cake. http://www.trials.com.au/phpBB3/viewtopic....;p=14851#p14851

I hope they do make new OSSA MARs again. They are very nice to ride. Yes that OSSA my wife was riding in that photo still runs. I fact it runs and rides like a dream. Here is a more recent photo it and having the M49 in the photo probably makes it a legit photo for the Bultaco forum.

Sorry its not a Bultaco but its closer than a Beta or a Yamaha and I didn't have to stage a photo. I had forgotten about this photo which was taken in about 2005.

Even with road pressure, competition trials tyres are terrible when you lean the bike in a turn due to the squareness of the tyre profile. To answer your question, 14 psi front and rear is usually enough to prevent overheating the tyres at high speed on bitumen.