feetupfun

The oil ratio you use depends on what you use your bike for and the conditions under which you ride it. For trials work (in sections) the engine doesn't need much oil in the petrol. If however you are going to use your bike to ride along a beach in soft sand, or to cruise up the highway at 100km/h, or to climb mountains that require lots of open throttle work, it is prudent to use more oil in your fuel. As well as the type of riding, it also depends on how hot the air is where you ride and if you ride with mud on the fins. Where I ride it gets extremely hot in summer and some bikes just stop running due to fuel vapourisation problems. You can hear the fuel boiling in the carby. Higher engine temperature usage should be matched with more oil per unit of petrol. What one person gets away with in their riding conditions may bring on high wear rates and maybe even seizures in another person's riding conditions.

I just took a very old front trials tyre off a recently acquired M49 Sherpa and thought it felt a bit heavy. It is a Firestone made in Spain with vee pattern blocks and is worn down to about 3mm block height. The worn out old Firestone weighs 4765 grams while the slightly worn 2003 tube-type Michelin that went onto the bike weighs 3506 grams. For non-metric people that is a weight difference of more than 2.5 pounds. I hate to think what an unworn Firestone would weigh. The sidewall of the Firestone has a little brag label saying "gum dipped" which I guess was a pretty cool thing at the time. I can't bear to throw it away as it is a terrific reminder of how much tyres have improved since 1970.

If you want the best shock action, buy Falcon. If you want to keep to a tight budget, buy NJB.

Ok I've found a reference chart for TY175 engine numbers vs model and year attributed to John Cane and printed in VMX magazine issue 18. I'm not going to spend half an hour typing it out but here is what you will need to post or PM to me if you want a dating for your TY175: If it starts with 525, the first two digits after the 525 If it starts with 1N4, the first digit after the 1N4 If it starts with 1R1, thats enough. If it has a different prefix to those above, it may have started out as a TY125.

For a manual, watch eBay. One will come up. A good starting point is: 6psi front 4psi rear No you wont hurt the sidewalls unless you smash the rim into something hard at speed in which case yes you will cut through the sidewalls and tube. If you ride at high speed in warm conditions you might overheat the tyres so if you do much road work, you may need to pump them up for that use. It is impossible to find decent grip off road with trials tyres at tyre pressures much above what I have recommended. Many newcomers are worried about getting flat tyres when using trials pressure so you are not alone. David

Yes it is OK and an economical option to have the silencer patched. It's a common sight on pinkys. Yes there is not much tyre clearance on the pinky. If the rim is true, the problem may be that the tyre has sat parked in one spot for a while. Pump it up to 20psi until you are ready to ride it. That will help a bit. Then riding it at normal trials pressure should get rid of the rest of the lump in the tyre quite quickly. If you have some way of warming the tyre before riding the bike it will recover shape quicker. If the rim is out too much, you may be able to get it straight using spoke adjustment. A few mm run out is usually OK on a trials bike unless you are going to ride it fast on a road. If the spoke threads are frozen, you may need to replace some or all of the spokes (about $100 for a set of spokes for one wheel). Put some penetrating oil on the spoke threads now if you want to try and adjust your spokes. It is normal for spoke threads to sieze up within a few years from new unless they have been treated with antisieze early on. Have a good look at where the tyre fits to the rim and see if it is evenly seated on the rim. Some tubeless tyres (Dunlop especially) won't stay in position on rims like your pinky so one part of the bead stays in a bit. This also causes the tyre to appear uneven when rotated. Your bike really should have a tube type tyre if you want it to fit properly and easily. If it is a Dunlop rear it is a tubeless type. Michelin make tube type and tubeless type. A Michelin X11 tubeless will probably be OK on your rim if you can't get a Michelin tube type.

There should be three digits at the start. That will determine the type of TY175. If it is the type that has the stand on the swingarm, it will be 525. If it is one of the models made to meet road rego requirements in some countries it might start with 1N4 or another set of three digits. The digits after the hyphen tell you when it was made which is of very little importance generally as all the bikes with the 525 prefix are mechanically identical no matter when they were made. I don't have the reference for the second set of numbers handy. If no one else posts it in the meantime, I will look it up and do another posting tonight. What is the thing about not wanting to post the engine number?

Yes welding and lots of machine shop work are required. Yes it's quite expensive. If you have to pay someone to do the work it would cost probably more than most people would be prepared to pay for a whole TY175 in good condition. The worth of it to you depends on how you value engine performance. They go just like you would expect a TY175 that was made to 205cc ie it has about 17% more torque at the same RPM.

To answer your question about the age of the TY175, yes the engine number is a good place to start. What is it?

Is Bioethanol actually ethanol or is it car fuel which contains some (5% to 20%) ethanol? I wouldn't recommend either for a two stroke trials bike. If it is 100% ethanol you would need to radically rejet your carby to suit it and drain the fuel system and replace it with petrol each time you stop riding (to prevent corrosion of the fuel system). If it is car fuel containing some ethanol, it will still absorb water from the atmosphere into your (vented) bike fuel system but less than if pure ethanol. The wet ethanol would give problems with corrosion within the bike fuel system. Modern cars have sealed fuel systems so usually avoid this problem. The trials bike with a carburettor would also need to be rejetted to suit the different fuel, if you want to retain smooth running. Again modern cars usually have fuel injection which avoids problems with the minor change in fuel properties.

Thanks Terry. It sounds like yours is the first model TY250 which some call TY250A. The cylinder porting and a few other less important motor internals on these is different to the later TY250 twinshock motors. A standard TY250B and later TY250 twinshock motor will pull noticably harder at low to mid RPM than the first TY250 due to their improved porting. The other changes between the first TY250 and later models is that the later ones have a lighter conrod, lighter(mass)clutch and a heavier flywheel weight. This means that one option for you for more grunt is to get the barrel and head from or fit a whole motor from a later model TY250. Another option for more grunt is to big bore your motor to 320cc which requires a bigger cylinder sleeve and piston, the head welded and machined and the crankcases machined to suit the sleeve. You may also need to raise the cylinder with a barrel spacer if the piston you use has a lower gudgeon pin location. Another option for better low RPM power is to fit boyesen reeds and a reed case spacer. An option for more power in the midrange is to have a specially designed expansion chamber and muffler made up to replace the standard exhaust. I suggest that you have a ride of an unmodified B or later model TY250 before you decide on a course of action.

Please tell us which TY250 you are talking about. There are three different TY250 twinshock engines (TY250, TY250B and the later series from 1976 onwards with prefix 493) and then there are the air-cooled monoshock series engines and the watercooled TY250Z models.

Strength of spark Have you set up the stator coil laminations to be as close as possible to the flywheel magnets without touching? Timing sanity check Why dont you make your own marks so you can use a timing light? Just set the piston at TDC and make a pair of matching marks in a convenient place. With your strobe you can then measure the advance. You will know if the timing is somewhere right if the distance between the marks (around the flywheel) is something like 20 to 25mm at low RPM.

It takes me nearly a year to get a new bike going to its full potential so for me there is no way I would want to get a new one every year even if it did make economic sense (which it doesn't). Here the resale value of a well maintained trials bike which starts out at $9000 goes down about $1500 after one year and then goes down $1000 for each year after that until it gets to about $3500 where the value is mainly determined by condition of the bike.

Hi Nitjay The whining noise is just one of the good reasons to have the Yamaha engined Scorpa. The whining sound you are hearing is produced by the straight cut primary (crankshaft to clutch) drive gears. It is usually loudest just as the clutch is engaging under load. Many other bikes have angled gear teeth in the primary drive to prevent this noise. I personally reckon the sound is very cool because it means that the crankshaft and gearbox is free of axial loading and less of the motor power is being lost in that part of the transmission. There is absolutely nothing to worry about from this noise. The motor in the SY250 is actually quite mild as far as primary drive noise is concerned. My 1976 KT250 has the standard straight cut primary drive gears in perfect condition and is so loud that spectators can clearly hear the whining as I ride past. If you are seriously into the mechanical noises of your bike, do this noise test: Warm the engine up fully and ensure the clutch plates have let go. With the bike stopped and motor idling, listen carefully as you shift into neutral. There should be a change in noise (gears rattling but nothing to worry about). Again listen carefully as you then pull in the clutch. There should be another change (clutch plates rattling and again nothing to worry about). You sound like just the guy to enjoy that sort of thing. You aren't the only one into motor noises. One of my favourite videos is a local club production which has a great sound track including the primary drive whine from a Yamaha TY250Z (same engine as yours) and a KT250 as they ride past in sections.

A recent post in this forum mentioned that John Shirt had success with improving the fork action on TY250 twinshock forks by using smaller oil holes in the damper rods. My TY250B and TY175B both have TY250 twinshock front ends fitted with B&J Racing springs but otherwise are standard. The B&J springs made a great improvement in the fork action of both bikes but they still don't seem to be as good as well set up Spanish bike forks of the same era. I weigh 88kg and use 5WT in the 175 and 10 WT in the 250. Oil level in both bikes is 125mm from the top when bottomed. Does anyone know the size and location of the holes that worked well for John Shirt?

Firstly are you sure that larger pistons are not available. Genuine Yamaha pistons go to 1.0mm oversize. Other brands of piston larger. Resleeve should be able to be done in the US and cost about $200US to $250US (parts and labour not freight). Costs $300 to $350 Australian done in Australia.

Those of you who store your bike with the clutch disengaged (lever pulled in)are increasing the sag rate of the clutch springs. This is like storing your bike on the trailer with the forks compressed. The springs will sag faster than otherwise. For bikes with hydraulic clutches, it may also have a negative effect on the hydraulic seals. The Alan Bechard clutch plate freeing technique mentioned above is by far the kindest to the bike's internals overall.

I am old and heavy too and ride both twinshock and modern and do find that when practicing, I get tired faster on the modern bike. I suspect that riding the modern bike is only more tiring because I tend to practice ride on terrain that is more severe. On a twinshock I can ride for hours mainly because the type of riding is less physical. For any given trial though, riding the same lines for the same number of laps, the modern bike is less tiring than a twinshock, no matter how good it is (and SWMs are very good) to complete the trial. The ergonomics, light weight, light controls and being able to leave the engine running all day make the modern bike easier when everything else is the same. I hope this helps

I'm a Rev 3 rider and I put up with the original stator failing because: 1 The original stator has now been rewound locally by a place I trust to have done a much better job than the original and it didn't cost much. 2 Beta Rev 3s are great to ride ie they suit my riding style. 3 It is better to ride a bike that you know has a couple of easy to fix problems than to ride one which has many hard to fix problems. If your Gas Gas has been reliable and you like riding it, why do you want to change?

I know these sounds too simple but I have seen both happen a few times so here we go. Step 1 Pilot jet blocks somehow. Step 2 Owner takes off carby including fuel supply hose with filter attached and cleans out pilot jet. Step 3 Owner refits carby and fuel line, this time the filter is installed opposite direction to previous. Step 4 Pilot jet blocks soon after from junk washed out of filter. Optional Step 2 Owner takes off carby leaving fuel hose and filter attached to fuel tap. Junk enters fuel hose while carby is disconnected. Step 3 Fuel washes junk into float bowl after reassembly. Step 4 Pilot jet blocks again. Another mode of pilot jet blockage: Junk gets into the pilot jet via the pilot air hole in the carby bellmouth (usually when the carby is being reinstalled)

I'm still not convinced from what you have written that there is something wrong with the jetting and I don't want you to go on a wild goose chase. The four local completely standard 348 Cotas in my area all perform very similarly and all have lots more low and midrange torque than a TY250 twinshock (434 and 493). If your 348 is actually capable of being ridden and continuous running yet won't even lift the front wheel, there is probably something else wrong other than the carby jetting. Because you have told us that you have the ignition set right, replaced the crank seals and the compression sounds OK, I'm assuming you have not checked the following other possibilities for problem sources: Blocked or otherwise restricted exhaust pipe/exhaust port Restrictive air inlet/non-standard airbox/incorrect air filter medium Leaking air hose between carby and barrel Incorrect port timing ie a ported barrel or a barrel from an MX or enduro Montesa or the piston skirt shortened at the back. PS Are you sure you have not set the timing 1.8mm after TDC rather than before TDC? PPS 80:1 synthetic oil ratio is quite extreme for an air cooled bike. I would suggest somewhere between 30:1 and 45:1 David

If the 348 runs reasonably smoothly at most throttle positions and RPMs with your new VM26 carby, the problem you have with your rice pudding is probably something other than the carby jetting. If the jetting is wrong, it will run either rich (4 stroking and lots of exhaust smoke) or lean (flat spots and pinging) or won't run at all. The rice pudding description is not enough info to go on. Is it a standard modern off the shelf VM26 carby bought from Mikuni? Is it an OEM Mikuni VM26 ie made for a 1970s Yamaha, Suzuki, Kawasaki? Is it a modern carby jetted for a Beta reed valve trials bike? They are all VM26 Mikunis. You can look up the standard jetting for a VM26 from the Mikuni website. If you want more help, please give more info about the symptoms and the type of VM26.

Johnnyboxer Those pegs on the bike in your post look exactly like the ones I bought from Sammy Millers and mounted on my TY250B. I think they were called "universal folding footpeg kit". They are quite good to ride with but the plating is a bit thin in places. David

Your symptoms are typical of a clutch that drags slightly. Question 1 Has the problem developed over time, or did it happen suddenly, or did you just buy the bike and have no history of the bike's clutch action? Question 2 Do you have wide experience of different bikes clutches to judge if yours is abnormal? I only ask this because there are not many trials bikes that can easily select neutral with back wheel stationary and the motor running. If there really is a problem with your clutch, you will need to take the clutch cover off and do some visual checking of the clutch. Check 1 Watch the pressure plate as you pull in the clutch lever. To avoid clutch drag, the pressure plate must move evenly ie stay parallel with the plates. If it moves away from parallel, you may have a problem with the springs. Check 2 Find out how much the pressure plate should move with the full travel of the clutch lever and check how much yours moves. If it not moving far enough, the bike may have the wrong clutch lever and/or mount assembly giving not enough travel of the cable. Another possibility is a problem with the mechanism that converts cable movement to clutch pressure plate movement. Check 3 If all this is OK, make another posting saying what you did find and I will suggest what to do next.