feetupfun

The product HAM2 was talking about was "tyre grip" in an aerosol can that the advertising blurb reckoned was good for icy roads and was a resin coating that was applied with alcohol that evaporates. Are you sure that is the same stuff that the go-kart racers use? I'm asking because a resin coating will make no difference to the hardness of the rubber while others are talking about the karters measuring the hardness of the rubber to avoid going too soft. There is also the thing about it being in a WD40 pump pack or an aerosol can that is not clear at all. I think there might be two different products being talked about here. One is "tyre dope" that may well be relevant to us wanting to soften old trials tyres and the other is resin to use on your car tyres before driving where there might be ice on the road. Does anyone know what the "tyre dope" is and how it works?

If there is oil in the pump it will be OK to do that. If the pump is dry, it might eventually damage the pump depending on how long you ride for.

Because you don't know what is in the fuel tank, and the oil pump may have lost prime over time, or have been disconnected from the cable because of a problem with it, it is safest to mix up a batch of new premix fuel before you go riding and get rid of what was in the tank when you got it. If you want to reinstate the injection system, it should be primed by hand to get all the air out of the system. There is a bleed screw on the pump and once that has just oil coming out operating the pump by hand, then put the screw back, remove the line at the point it goes into the motor and keep pumping by hand until all the air has come out. You should also check the pump settings are right. There is a line on the cable pulley that should line up with a pin on the pump plunger when the throttle is closed. There are lots of things can go wrong with an injection system so there will always be a risk of lunching the motor.

Im intrigued with the chemistry going on here. Do you know why the karters are washing off their tyres? Also what is the process going on with the WD40? I'm guessing they don't use the tyres for a while after putting on the WD40? There may be something valuable in this washing and WD40 thing for trials tyres too

The oil pump resides underneath the oil pump cover and is attached to the Right hand side engine outer cover (I call that the clutch cover). You have to take the clutch cover off to get the shaft out because the gear on the inner end of the shaft will not fit out the hole the pump drive shaft goes through.

You need to take the clutch cover off, and fit a little cover to seal off the hole where the pump was

I agree with what Tony said and yes I know of two Yamaha single cylinder two-stroke motors that siezed because the oil pump stopping pumping

I suggest you first measure the voltage difference between the motor casings and the frame. If there is a voltage difference, then your motor is not grounded to the frame (and it needs to be grounded to the frame)

I like lots of things about Dr Who. One is the way they include self-mockery like when the Doctor's Daughter says "I like the running" Tim I have to agree - that "don't blink" episode is my all-time favourite Dr Who. It even scares my kids

To make the head angle steeper, I lengthened the frame backbone 25mm and made a bend in the front tubes at the motor mount To lengthen the swingarm, I extended the axle plates 45mm Mine actually looks quite standard unless you look closely, which was my intention If you send me your email via PM I will send you photos of a TY175-based bike that you would probably be interested in seeing for ideas for your "far as I can" bike

Its not the carb size or the air filter design that limits the performance

Its hard to tell from what you have written, but it sounds like you might be measuring voltages of open circuits. If the ground wire in the headlight circuit is 19V above the frame voltage, then the "ground" wire is not grounded. To find out what voltage the bulbs are seeing at different RPM, measure the voltage difference between supply and ground with the headlight and taillight both on. Some bikes do make too much voltage at high revs even with the correct bulbs in service and good earths. I used to use 12 and 24 volt bulbs in my (nominally 6 volt) 1970s Japanese trials bikes and trail bikes to avoid blowing bulbs. I have seen many other techniques successfully used too.

Yes you have described a sticking clutch. To free up clutch shift to top (5th) gear, pull clutch lever in and rock bike forwards and rearwards. The tyre will grip better in the rearwards direction so concentrate on maximising your effort when moving it rearwards As previous person said, clutch issue has nothing to do with motor not starting. If it ran, now it doesn't, ask yourself "what is different?" Usually that is engine flooded with petrol or no petrol getting to combustion zone.

I use automotive acrylic lacquer for frames but I'm sure there are many other suitable paints.

Gloss black is the right colour for the Cota 348 frame. The brace pieces that go from the swingarm pivot to the cylinder head are plated decorative chrome

Looks like the 4 stroke has a non-linear cable pull ratio. This is usually done to smooth out the action of the throttle when it is near closed. Trimming the ramp to make the action more linear will not help you with off-idle throttle sensitivity because the ramp is the bit that affects throttle opening at the other end of the throttle action You need a tube that has the cable end holder following a smaller diameter circle - like the other one in your photo

One TY175 I have came with a 26mm Mikuni from a DT175. It now has a standard TY175 carby on it because with the 26mm carby it did something that put me off a bit. It felt exactly like a normal TY175 below about 6000RPM. If you accellerated at full throttle through 6000RPM it would suddenly accellerate faster at that point, much like the way a two stroke MX bike does, but much milder. It was a bit disconcerting for me when riding obstacles that require full stick. Because of this, and because the bike is a loan bike for trials learners, the standard carby is probably better. For trail riding on that bike, the 26mm carby is definitely a hoot and helps with big (sustained) hill-climbs.

Earlier this year, I actually went through the process of modifying a TY250 frame to make a replica of a bike which was built in 1976 and which used very similar ideas to what was done years later with the Yam frame Majestys. It was quite a learning experience and as people say, a lot of work to do it right. It took me 4 full working days to make the jig and do the basic frame mods. It doesn't sound much but that is 32 hours work and that does not include the myriad of other work that is needed to be able to complete the bike. It is definitely not easy and I would agree quite impossible to do properly without making a jig first. In the case of the bike I did, the target was to raise the motor 1 inch, and from all I have seen and read about the Yam Frame majestys, I would say that was the case with them too. The claimed 2 inch increase in ground clearance and steepened steering head angle were achieved via the combination of raising the motor close to one inch and the increased rear end travel raising the rear end of the bike. Having studied photos of Yam framed majestys with tank removed, I know by comparing the locations of the sparkplug tips relative to the horizontal brace behind the toolbox, that they had the motor raised the same amount or very close to the one I did. I'm not keen to post up photos of how the work was done yet because that bike was built for a feature article in a magazine and it hasn't come out yet. I do plan on posting the photos up somewhere accessible later on.

It is an older Beta motor but does not look like a Zero motor to me. They had cylinder castings with flats. This one is round. Cylinder doesn't look right for the Beta Synt models either

From what I have seen, the other Montesa trials bike square section fork bottoms from the same era look the same as the 348 and probably are

As well as those things Tim said, if the fuel evaporates out of the float bowl over time (fuel tap off and does not pass), it leaves a viscous oily residue coating on everything that it was touching that takes a while to wash off when you turn the fuel on next time. I find that I get restriction in the pilot jet from this residue that makes the bike run poorly for a few minutes after not being run for a few weeks. With longer term storage (with the fuel tap left on or passing) a solid polymer film can form on the surfaces that the petrol touches and it can be very difficult to remove the film.

1974 was the first well-known Yamaha single-shock trials bike. It was a Tilkens (non-linkage) design rear end like the early YZ and MX Yamahas. Mick Andrews rode the SSDT on it that year. The first Yamaha linkage-type single shock trials bikes were in existance in the early 1980s as development bikes but the design was not "revealed" until 1983. There were probably home-made single shock trials bikes before Yamaha started making them.

Not a dumb question at all. Yes some people run with less spark advance than standard on trials bikes, especially on large capacity motors. The standard setting is only a guide. Why not try it and see what you think. The motor will run even with the spark after TDC so you can experiment to your hearts desire. To start with I would try 10 degrees BTDC and see if you can feel the difference. Remember to test for the effect on high RPM performance as well as low RPM response.

Wossner are making pistons 4 mm oversize for some patterns so that might be the source for a 74mm TY250 piston.

Replacement (unobtainable) magneto covers for Yamaha TY250 twinshock or TY175 Twinshock bikes would probably be suitable parts for the case study although they would be less of a challenge than a one-piece airbox.