feetupfun

If you want to check if your timing is right with a timing strobe, it should be about 22mm BTDC as measured on the OD of the flywheel. You will probably have to make your own marks on the flywheel because Yamaha did not mark them. You will know when you have everything right because with the TK carby, and everything set to normal, that motor is one of the smoothest and most even running two strokes you will find, and has plenty of stick to boot.

Hey Pete Bulpedro. I agree with you about the M85. They are quite OK once geared low enough. The closest Alpina to the Sherpa T of the same vintage. The M85 was my first Bultaco and I rode it in trials and enduros back in 1976. I remember it cost $450 and in quite sad condition when I bought it in 1975. Here is a picture taken in 1976 after I repainted it.

The 348s all came with the same wheelbase. The first 349 (the one with the red tank with a tube in the side of the tank as a depth guage) has a wheelbase approx 25mm longer than a 348. The next model 349 (the White Wonder) has a wheelbase the same as the 348s. The 349 frame is not just missing the tubes under the engine and at the rear loop, but is also more compact vertically around the seat/tank junction area. The gearbox output sprocket on the 348 is on a taper. On 349s there is a quick-release mechanism and spline. The RH engine cover is different from 348 to 349 (to allow rapid change of sprocket) The 348 came with chain guide tubes. 349 came with a spring loaded tensioner. The White Wonder 349 has the fork tubes closer together than the 348. Not sure about first model 349. The gear shift indexing on the 349 has a slightly different ratchet arrangement which made shifting more positive. The 349 has a huge muffler compared witht the 348. The 348s came with 1" handlebars stepped down at the ends for the controls. 349s came with normal 7/8" bars. The 348 is a mighty tractor. The 349 is even mightier. Both take a lot of oommph to kick over. They are both pretty much the same weight.

Use top gear not third and let it warm up. The higher the gear, the greater torque on the clutch. Another thing that will help with communication - if a clutch is engaged, it is transmitting torque. If it is disengaged, the plates are slipping past each other.

With new slide, new needle (U) and new needle jet (107), standard pilot jet and correct float level, it tends to 4 stroke just above where the pilot jet effect is strongest - and runs great everywhere else. I've then raised the slide cutaway in stages as far as I can and the 4 stroking is still there. The next thing I want to try is a 106 needle jet instead of the 107, hoping to get it slightly leaner at that part of the needle. I've also ordered a needle as used in the 238cc Sherpa T with Mk 2 AMAL to experiment with if the 106 needle jet doesn't get me what I want. Yes it costs a small fortune to buy the AMAL parts and economically it would make much more sense to fit a new Mikuni - but I seem to enjoy the challenge. If I wanted things to be easy, I wouldn't ride 35 year old Spanish trials bikes.

A 26mm VM Mikuni will fit directly to the engine side connector, but the Mikuni inlet bell OD is smaller diameter than the AMAL mk2, so you would need to fit a sleeve. I have done a test fitting on my 348 with a 26mm VM, but am persevering with getting it to run right with the AMAL at this stage.

What conditions of load, throttle, RPM is the motor under at the time the motor is pinking? How can you tell it is getting too hot? Is the bore/rings run in yet? Is the carby getting enough fuel (blocked fuel tank vent?) If you have still got the rubber silencer in the airbox lid and the big boxy muffler, the jetting will need to be 1N4 series TY175 rather than 525 series TY175.

My 1981 Godden 250 frame has the same diameter bearing seats in the frame as the TY250 and TY175

I've so far fitted tube type IRCs to the rear wheels of: TY250B Majesty (TY250D wheel) OSSA MAR MkII (shoulderless Akront) and found that after a bit of perseverance and leaving them pumped up to 20psi between rides, that the IRC stays on these rims at 6psi. I also find that the tube gets moved around in one direction inside the tyre.

Yes that is a good idea your friend suggested. I ground down an 8mm section of hex key to 7mm A/F and turned it with a single hex socket and yes it was tight all right having never been off before.

The only other thing I thought of after looking at the photos again was to make sure your puller contacts the back of the gear evenly so you don't damage the ends of the teeth.

Sounds like yours is a bit low geared. The rear sprocket should be 33 teeth, which is small compared with other twinshocks. When they are running right, a 348 will pull very strongly. Maybe you can gauge the performance if I tell you that on the 348s I have ridden (and there are 5 in our local club, one of which is mine) you can take off in 4th gear sitting down and accellerate to about 60km/h from a start with the front coming up after the first 15 feet, without pulling up on the bars. Standard gearing provides a top speed in 6th of about 120km/h and it gets to that speed very quickly for a 1970s trials bike. Another guide for if your bike needs rings is that I'm 95kg, and find I have to ease it over compression before I kick start the motor. If your "chip" is like a "plink" then it may well need a small end bearing. Piston rattle noise is more of a gentle knock, mainly on overrun. I don't know what pressure it should generate on a compression test. Mine still has the cross-hatching in the bore from new, but has mild piston rattle on overrun from high RPM, and fabulous compression. If you have another 348 nearby, you could compare engine noises. The standard exhaust and air box is very effective at silencing the breathing noises on the 348, so any mechanical noise will seem loud - relatively speaking.

The rear wheel looks like a TY175/250 twinshock but has a brake plate from some other jap bike of a similar era. Without seeing inside or the other side, it is hard to say for sure. The front wheel looks like a TY175/250 twinshock but has a brake plate from some other jap bike of a similar era. Again it would help to see inside and the other side. Neither is anything like the wheels from a KT

If you want to stop the hole getting punched out of the ignition case again, use the RH footpeg to stop your foot when you are kicking. That way the kicker can return forwards out of the way when riding. A less ergonomic approach is to fit the kicker vertical when is the stored position to prevent over-rotation of the shaft when kicking. Tell every one that rides your bike how to kick it. Don't put much air pressure in the forks if they are the type with soft springs and air caps - the seal friction makes the forks sticky. Add spring preload and use heavy fork oil if they are too soft without air pressure, or buy stiffer springs. The gearbox output sprocket is on a taper. When you need to replace it, a 100mm angle grinder can be used with care to remove the old sprocket. Once you get to within 2mm of the shaft with the grinding wheel, the sprocket will come loose. To change the LH crank seal you will need to know this: The primary drive gear on the crankshaft is on a taper. Finger type pullers will not get it off, even with heat. A suitable puller can be made or probably bought from a Montesa parts specialist. If you do a search in these forums you will find photos of one I made at home. There is a Facebook Group dedicated to the Cota 348. The rubber straps are still available but not cheap. The clutch engagement action is interesting. If you use the sort of oil that is normally used in wet clutches, clutch engagement is very sudden and harsh (these bikes were never meant to be ridden on the clutch). You can successfully use very heavy oil in the clutch and primary drive to reduce the effect without causing problems with drag, provided the clutch opens evenly. I use car manual transmission oil quite successfully in mine. No matter what oil you use and even with the fanciest cable and lever, the clutch pull is a fair bit heavier than other trials bikes of the era, and the clutch spring preload is not adjustable. After many years I find I just ride it with the clutch out and control tight turns with the rear brake. If the motor is tuned well it will not stall even at incredibly low RPM. Some people remove the primary drive side flywheel. I don't know why because they accellerate great with it in place anyway. Don't rush to rebore it because of a top end rattle. They do tend to rattle a bit even with everything in perfect nick. Standard thickness for the crankcase centre gaskets and crankshaft seal carriers is 0.5mm. If it still has the MKII AMAL concentric carby, you will find that the needle and needle jet require frequent replacement due to wear. Be careful to get enough torque on the ignition flywheel nut - they are known for the flywheel location key shearing. The handlebar levers need to have high leverage ratio similar to the original AMAL levers, or you will probably have trouble pulling in the clutch. Dont worry about using a Domino twistgrip. Your Domino will be much better than what came on the 348. If you have the original 1" Akront handlebars you are lucky, they are a great shape and very strong. If I think of more I will do another posting

The plastic bag is a waste of time. Moisture forms on the bearing from the atmosphere after you take the bearing out of the freezer - it's bone dry inside a freezer.

Wow I had no idea you guys in the UK were such trusting gentlemen regarding the rules. Over here it is fair game to take any route that gets you through your own colour gates. As a consequence, we tend to use a lot of tape to limit creativity of line selection to that line intended by the C of C. In the case of that diagram, there would be red tape joining the middle three red arrows. For bdmc (applying your rules for not going through a gate of another colour to the section in the diagram), how does the red route rider get out the end of the section without going between the two blue markers?

12 Stone + TY175 = Falcons with 50lb springs

You will find a button if you become a Site Supporter

You can do it by becoming a Trials Central "Supporter" or by posting it in photobucket and putting a link in your TC posting.

Metal shavings = pull that fork leg apart to investigate. Many possibilities for cause. Not worth speculating.

Yes the killswitch should earth the LT side of the HT coil when pushed. Dunno about your blue wire though - I think all my TYs have a black wire to the LT side of the HT coil.

A bent tube or bent tubes can cause this effect. You should be able to check for this by loosening off the tube clamps for one tube and the axle clamp and rotating the fork tube within its clamp. Another way to find out where the stickiness is coming from is to put the bike on a stand and take off the fork caps. Move the wheel up and down through the stroke. That way you take the spring force and air pressure out of the equation.

You can use less of a modern semi-synthetic or semi-synthetic two-stroke oil than what you would have used of a basic mineral-based two-stroke oil in the 1970s. How much less depends on how game you are, how hot it is where you ride, how you ride and many other factors. I live in a very hot place and sometimes get my 1970s trials bike motors very hot so I use 3% (33:1) semi-synthetic. Good quality modern oils produce very little smoke if the jetting is good, even at 3% mix. You have to make a very large change in oil/fuel ratio to affect the fuel/air mixture. If you used 5% (20:1) in the 1970s and want to run 2.5% (40:1) now with modern oil, you will probably not make a detectable difference to the way the motor performs.

Sorry but there are plenty of different types of rebuildable shockies, old and new, and there are plenty of old, rebuildable shockies that are not worth rebuilding. If you post a picture of what you have, you will probably get a much better answer. Don't worry, there is a potential goldmine of information about shockies available from contributors to this forum.

That kickstart on eBay appears to be the wrong shape to work well on a TY175