feetupfun

The "air" is meant to be nitrogen and I have found that 70-80 psi works fine. 25 psi is probably a little low for the seals to work properly.

Using the (64mm stroke) Alpina crankshaft and top end is a common mod for people who want more grunt than a 325 Sherpa T provides. The Alpina port timing and compression ratio is fine for trials. My Alpina 138 is an overbored (360cc) 64mm stroke motor and the performance is quite refreshing on big hills - even with the standard 27mm carby and exhaust.

Yes there are different model 349s The first model was 1979 and has a red tank with fuel level sight guage in the side of the tank, and has a longer wheelbase than the later models. The white tank one in the photo is the second model 349 and is sometimes called the "white wonder" Third and later models also had red tanks.

Dave you aren't the only one I confess to assembling my M138 Alpina motor (my first Bultaco engine rebuild) three times in 2003 before I got it right Attempt 1 - crankshaft wrong way round (I managed to do this by holding a conversation while I worked) Attempt 2 - one shift fork installed backwards (it looked OK and fitted together nicely, but would only allow 1st and 2nd gear to be used) Attempt 3 - hooray, it all worked and has ever since!

The crankshaft bearing issue can be tricky if you look at repair manuals because some 5 speed motors have two bearings on one side and one on the other while others have only one bearing on each side. A point to note is that some people use a roller bearing one side to better allow for differential expansion between crank shaft and casings. This also makes assembly even easier. The ball bearing in the other side holds the crank in the middle. Another point is that the 5 speed Bultaco motor has a tendency for the main bearings to spin in the casings. It's usually no big deal, but it is a good idea to have a good look at the bearing seats in the cases to see of yours has had this happen. If the old bearing outers have been rotating, it is a good idea to have the bearing seats sleeved back to the correct size, using either steel or aluminium sleeves, to reduce the risk of it happening again. Providing enough bearing (balls to grooves) clearance is important because unless there is enough clearance within the bearing, differential expansion (crank to casings) will eventually work the bearing seat fit loose either in the cases or on the crank (as well as putting a lot of side loading on the bearings).

AVGAS is fine if the sparkplug heat range is right. I don't know what pump gas to recommend otherwise because your pump gas is likely to be quite different to our car fuel. We can buy 98 Octane unleaded car fuel from the bowser, has no ethanol in it and it works fine in all my air-cooled trials bikes. Standard car fuel here is 92 octane with no ethanol and it does not go quite as well in the bikes as the 98 octane. We also have 95 octane with ethanol which I only use in my car. I suspect all your unleaded pump gas varieties will contain ethanol and that the ethanol may damage your fibreglass fuel tank. My recommendadtion for your OSSA is to use an NGK B6ES plug and AVGAS premix, and if it fouls another plug, work out what is causing the fouling by inspecting it closely.

If it runs fine up until the plug loses spark it is possible that the problem is lead fouling from the AVGAS you are using combined with a too hot or too cold heat range plug. Have a very close look at one of your fouled sparkplugs (magnifying glass) and see if you can see anything unusual ("hairs" or yellow/orange patches on the nose can indicate lead fouling). It is a waste of money using iridium plugs in a bike that fouls plugs. Another possibility for frequent plug fouling is is your bike has been run on unleaded fuel previously, running on leaded fuel may be causing some combustion chamber deposits to come off and stick to the plug nose.

If your Mk 1 AMAL is making the motor run rich from 1/4 to 3/4 throttle, it most likely has worn jet needle and needle jet. Those parts wear rapidly on that carby and replacements are available from AMAL carby suppliers It may also have a leaking float needle valve. Your OSSA questions will probably be answered better in Twinshock because Classic is usually used referring to pre-1965 bikes

This is from the Yamaha TY250A parts book: Pilot jet #50 Main jet #114 Slide cutaway #3.0 Slide needle 5C92-4 Needle jet is called "nozzle-main" Yamaha part number 434-14341-00 This is from a tune-up book: TY250A 434-000101 onwards Carby model Teikei Y26P Float level 21mm Starter jet No 90 Air jet 2.5 Air screw 2.5 turns Pilot jet No 50 Main jet No 112 Jet needle/clip position 5C9Z-3 Cut-away No 3.0 Needle jet S-85

I'll have a look this afternoon and post them up but you should be aware that the jetting numbers for that TK carby do not necessarily relate to Mikuni numbers.

Spot weld?????? If you electric weld (induce a strong, fluctuating magnetic field) near the magnets, they might not be magnets when you are done. If you flame weld near (heat up) the magnets they might not be magnets afterwards. I suggest two alternatives: Take the existing ring off, add your extra ring by welding and then refit it to the flywheel Take the existing ring off and fit a new ring the size you want to the flywheel

Use a Wiseco piston kit made for 1974/75 Honda CR250/MT250 Elsinore - it works with no mods required. Another alternative is to use a TS250/RL250 piston, but this will require a spacer fitted under the barrel.

Welding will damage the magnets. Additional weight is usually added as a band (shrink fit and fasteners) or as a disc (fasteners). If the previous owner has had machining done to a piece that is riveted or bolted on, you can take that off, weld on a ring, and then reattach the piece.

Step 1 is to work out if the problem is spark or fuel. Was the crankcase full of fuel? When you looked at the magneto, did the points have the right gap? Were the mating surfaces clean? Was the timing set right? Is the killswitch wire shorting to earth somewhere? Yes you can use any condenser made for points/coil ignition if you are fitting it under the tank. If you want to fit it inside the magneto, you will need to get the right one. Replacing the condenser will not clean up or reset dirty points. You need to start your problem solving at step 1 not step 15. You will need to provide much more info about the bike if you want it valued. From your description and location I would say it would be somewhere between $5 and $500 from what I have read so far. Maybe it is worth more, but you are not getting your information across. Can you post a decent picture of it somewhere - maybe on www.trials.com.au ?

I'm pretty sure it did not say TY175 on the Pro-X box but the box is gone now so I can't check. I suspect it said either DT175 or IT175. Some people have made out that there are differences between TY175, IT175, MX175 and DT175 Yamaha pistons and that these make a difference to the way the TY175 motor runs, but I have used TY, IT, DT Yamaha pistons over the years and have never noticed any difference to the way they run, and not noticed any differences to rear skirt length or crown shape or height. The holes in the back may have been different shape or size, but because of the reed valve, are not critical to the functioning of the TY175 motor. I have even used a CT3 piston in a TY175 back in the late 1970s and just cut the holes in the rear bigger to match the TY piston that came out, and it went fine too. Pro-X pistons are made in Europe somewhere (I forget where) using the same technology (metal and manufacturing techniques) as the pistons that were fitted to new Japanese bikes in the 1970s. Have a look at their website for details.

No I can't recommend any source for pre-jetted Mikunis. I bought a new "pre-jetted" Mikuni for a TY250 and spent many hours trying to get to run right and ended up giving up on it and rebuilding the standard carby. For the 348, I do want to try a KT250 Mikuni because they work well on both my KT and my 250 OSSA trials bikes, and being a piston port trials motor, I suspect the Cota 348 might also work well with the KT carby, but I haven't tried it yet. I suspect the reason the Mikuni you are trying on your 348 is not working well might be that it is jetted for a reed - valve motor.

What it is worth depends on the bikes condition and you haven't said much about that (except what the OD reads) or where you live. About the starting problem, how does anyone alse know what you have tried if all you say is that you have done everything you know? If the problem is poor spark, and the bike went well in the past, you should probably first check the condition/setting of the points.

Difficult to diagnose over the internet but the first thing I thought of was that maybe for some reason perhaps associated with the work you had done on the carby, the fuel level may be too high in the float bowl. Possibilities are sticking float/float needle, bent/broken/cracked float arm, leaking float (float doesn't float as high). High fuel level can cause fuel to be lost out the float bowl overflow and/or into the motor as you ride, and will cause the motor to run rich.

There has been lots of discussion on these forums already on this subject. Have you done a search on the topic? I use Pro-X pistons for 66mm - 68mm TY175 rebores

I'm pleased to report that I rode an event two weeks ago that has a tradition of encouraging the riding of older twinshock trials bikes. In previous years at this event there had been a ruling that bikes had to be made before 1980, but for this year the twinshock bike age rule was relaxed to align with the standard rules of the local licencing body, which has a cut-off date of 1987 (to intentionally allow TLR250s to compete). The pleasing thing for me was that out of thirty-something riders, all but one rode on pre-1980 bikes, despite many riders also owning post-1980 twinshock bikes. This is a nostalgia event that is run to maximise socialisation, and is seeing increased participation every year. At the other end of the spectrum, at the state trials titles event a few weeks before the above mentioned trial, every twinshock trials bike was a post-1980 model and there were only seven entries in the class.

The TLM 50 has 21"and 18"wheels. I've not heard of a TLM 80.

Hello back from 550km away. I hope you know about the Aussie trials website. You will find a strong following for TY175s amongst the forum contributors there as well as on these forums. www.trials.com.au Regards David

Hey Steve there are plenty of postings already on the Beta forum about your problem. Heres a search on stator http://www.trialscentral.com/forums/index....hlite=%2Bstator

I live in Queensland, Australia and the local Beta dealer has an exchange service, with the stators being rewound locally. The rewound stators don't fail. The only way I know of for testing them is to borrow one off a mate and see if it fixes the problem. Beware not all Rev 3 models have the same connections - I think yours will have a different number of wires to later model stators so you will probably need to find someone with a 2000 model if you want to test it out.

You have perfectly described the symptoms for the same mode of ignition stator failure that occurred on my 2003 Rev 3 Beta. Unfortunately, stator failure on Betas of that era are relatively common.