feetupfun

The tap filter is inside the fuel tank and is attached to the fuel tap. Filtering the fuel as it goes in is a noble act, but this filter may still be causing a restriction to flow. You did say you changed the tank cap hose, but didn't say that you tested the fuel flow rate to the carby. That would prove if there were any problems with fuel supply caused by tank vacuum or flow restriction. It is also possible to get a vapour lock in the fuel line that stops the fuel flow. I can't see the fuel plumbing on your bike to know if that is a likely problem or not

you didn't mention checking the filter in the fuel tap and you've got some pretty bizarre things going on there (a steering wheel and a kill switch on the radiator hose)

suggest you fit a new air filter before it gets sucked into the carby and reeds. The filter will be quite crumbly by now Not going to get into the premix debate also suggest you post in either "Yamaha" or "air cooled monos" forums

might sound a bit obvious, but some shocks only have damping when they are the one way up, while other shocks work either way up. For example, standard spec Falcons only have damping when the shaft is at the bottom. I've not had Rockshocks to know if they have to be a certain way up to work. I have had a terrific run with four pairs of Falcons since about 2003, and find the action to be extremely good in competition trials sections. All four pairs still work as well as when they were new, and they have only needed oil, seal and bump stop rubber changes to keep them going. For general (trail and play) riding however, I find that Falcons have too little compression damping and would recommend Betors for that, because Betors have more high-speed compression damping.

it helps to let the clutch partially engage a few times while you are holding the shift lever down (with the motor running). If it didn't go into gear fully before you do this, you should be able to feel and hear it going in fully by doing this. If it did go in fully the first time, there will be no extra clunk when you do this.

the best way to do non-invasive condition monitoring on the effectiveness of the rings in a two stroke is to look at the surface of the cylinder, looking for carbon deposits (brown smudge) in the area wiped by the rings. If the rings are leaking there will be a thin film of carbon there. You can use an endoscope through the plug hole, a torch or endoscope through the exhaust port, or take the head off to check this. If you have owned the bike from a time when you are sure it had effective ring sealing, you should be able to tell that the rings are worn by how hard it is to push over compression, and if the low-RPM end power has reduced. Some 2 stroke trials motors develop a 4 stroking/misfiring mode above mid RPM when the rings are worn out, but this is not a universal symptom. Sometimes it is necessary to rebuild the top end based on piston wear, even if the rings are still sealing OK. For this you will also need to have known how quiet the piston was originally, or to pull the cylinder off and do some measuring.

what little step? all I can see in your fuzzy photo of the steering head tube is the top bearing seat maybe its just a terminology thing? the seats in the headstock tube are what the bearing outers rest against. The bearing inners go on the stem/axle Bearing parts for those sort of tapered roller bearings are called outer race, inner race and rolling elements/cage

Top head stock looks normal and ready to accept upper bearing outer race Yes you need to remove the old lower race before fitting the new lower race Sammy Miller Products sells footpeg kits for TY175. The RH footpeg from the kit sticks out too far for the kickstart to clear it. Some people run without a footpeg spring on that side to allow for kicking. If you have to have a spring (to pass tech inspection at a trial) you can make a catch to hold the peg up when you start the motor. The SM footpeg kit pegs tends to sag with use. Also if yours is a TY175JC or TY175JE (with the stand mount as part of the LH footpeg mount), then you will lose your stand mount if you fit them. There are lots of better aftermarket footpegs but you would need to make your own mounting plates to use them.

If the conductor in the HT lead where you cut it was nice bright copper it should be OK. Plug caps can cause problems too and fitting a new one is pretty cheap. Some just keep turning even after they are fully screwed on because all you are doing is screwing the thread into the hole up the middle of the lead. Generally the cap is mainly held in place by friction between the OD of the lead and the socket in the cap. No you can't fit a new HT lead directly to the HT coil winding. Have you checked the LT wiring and the LT connectors for damage? If you still have the keyswitch fitted, you should do a test run with it unplugged at the coil end. You may have a problem with it's wiring or internally.

What about the HT lead and plug cap? Does it still have the original ignition keyswitch fitted (under the left side of the fuel tank)? A much better test of the rings sealing would be to look inside the bore for evidence of blowby (through exhaust port or plug hole or to take the head off). Compression tests give widely varying results on the same motor depending on how oily the rings are and how fast it is cranked over and for how many revolutions it is cranked over for.

whatever you want. Fixed points timing is set as a compromise for low and high rev operation. If you want to set you electronic ignition for the smoothest and most reliable response at low revs, set the timing to be a bit later than standard fixed setting at low RPM. If you want to maximise top end power, set the timing with the low RPM setting at the standard fixed setting. It really is something you should play around with until you are happy with how your motor runs for the way you like it.

Check the conductor inside the HT lead where it connects to the plug cap Check the HT lead for touching the exhaust - I've seen a few KTs with melted HT leads Check killswitch and killswitch wiring (disconnect it at the HT coil end) Do you know if there was any motor work done before you got it? (it might not have the right length rear piston skirt) Are the rings worn out, or not sealing for some other reason? (two strokes can still start OK but then run in a way that makes them sound very rich if the rings are not sealing well) Did you run it before you got the carby overhauled? (ie did you get the carby overhauled because of the problem) Are you sure the start enrichening device is closing fully?

I'm interested to see how you get a significant increase the steering lock. On most of the TY250Zs I've seen the owners have increased the steering lock by grinding the frame away where the fork tubes touch. This provides a modest improvement, but is still way less lock than what is on the air-cooled mono Yamahas. I'm sure you will enjoy riding the bike, the suspension action is well ahead of what the other bikes of the early 1990s had, the main frame cradle is amazingly rigid and robust, the big diameter forks tubes resist flex very well and the motor and gearbox are pure bliss to use. They are great to ride in everything except extremely tight stuff

Footpeg lowering kit? That would be pretty interesting on one of those bikes. The footpegs are already as low as the bashplate. I rode one of these (first model TY250Z) for a few years in the late 1990s and could not come to a happy agreement with some aspects of the design. What caused me grief was the very limited steering lock, and the long wheelbase. It made for a very big turning circle which might be fine if you like hopping the bike in turns, but I don't.

I think it was MT125 front end on that one. He has a couple that are very similar. The tank was custom made by the rider to clear the fork tubes and look something like a TL125 tank

The front end on this TL125 by Dan Gollagher works beautifully

same comments for MT125, CR125, MR175 front ends as for XL125 leading axle front end

I do know that there is usually no place to fit a compression release on modern water cooled two stroke motors because the coolant space encircles the spark plug. I suppose it could be dome with a lot of machining and welding. An old trick you might consider (but feasibility depends on the design of the cylinder casting) is drilling a small hole from the top side of the exhaust port and through the top end of the cylinder wall. If the hole size is chosen well, it will make it easier to kick over but make negligible difference to the way it runs. Another option is the Beta Alp (4 stroke 200cc Suzuki motor) which is electric start, but not really a competition trials bike

by the time it was 3 years old, our 24V OSET 16 had so many parts replaced there was very little left of the original bike

sounds like typical symptoms of blocked or part-blocked pilot jet

Some Montesa forks use an anti-bottoming device which can swell/bell causing the forks to stick, but that is when they are fully compressed, not half-compressed. It is also possible that one or both of the tubes is bent, and that when you reassembled them into the triple clamps, the bend/s might be causing a sticky spot. I would look for bends in the tubes. If they are both bent you may get away with aligning the orientation of the bends to be fore-aft and both the same way, so that the mudguard mount and axle fixing location holding the fork bottoms in the one position does not cause the bends to cause a sticky spot. Better still to have the tubes straightened. Maybe there is a little dent in one of the fork bottoms that combined with a slight tube bend, is causing the jamming. In this case you should be able to get them to move freely by rotating one or both of the tubes in the triple clamps so that the bend moves the "high" point of the tube away from the dent.

Need more info. You have not said if the shift shaft is frozen, or still moves. If the shifter shaft still moves freely through an arc, it is likely to be a spring broken or popped off behind the clutch basket (no need to split the cases). If it doesn't return to mid position itself after being moved, also likely to be a spring issue behind the clutch If the shifter shaft is frozen it might be bent, or maybe something else - more info needed. Is there any evidence of the shift shaft being out of position axially, or having had an impact? Is the circlip still in place where the shift shaft enters the gearbox on the LH end?

totally agree about the benefits of having an advance curve. That's why I put the ignition on my TY175. It is a 205cc engine and I wanted to make it harder to stall, and also retain top end power

I've witnessed the John Cane type (on one of my TY175s) and the Electrix type (on a friend's TY175) and they both work well. The only negative I have seen is that the Electrix one uses a very long HT lead because the HT coil is located down beside the airbox

LH (ABCD) DT175 crankcase halves are quite different to the TY175, most obviously where the flywheel cover attaches. The closest match would be YZ125C and YZ125X (the first six-speed motors of that lineage), but I have not tried to match up the big TY175 magneto cover to one of those, and they are far rarer than TY175 casings anyway. Later model (EFGH) DT175s with the 6 speed motors are also different where the mag cover attaches, and also have a completely different shift shaft arrangement. I suggest you persist in seeking a TY175 case because they do pop up on eBay. A friend bought a pair of casings here in Australia on eBay only a few weeks ago. You may have to buy a bottom end or a pair of casings to get what you want. If the damage is repairable, just get it to a suitable welding specialist. Maybe if you posted a photo showing the damage, you could get an informed opinion about if it is repairable or not.