feetupfun

Yes probably piston slap but may also be the primary drive gears if the crank end is running out. If the noise is from the primary gears the noise will be the same under most conditions while piston slap will sound worst while on closed throttle overrun from highish RPM. Spring loaded tensioners seem to be more popular than the chain guides. Theres a neat one available that mounts on the gearbox case. Have a look at what other riders use. Museum standard bikes will have the tube guides while many ride bikes have a tensioner.

Sorry no photo, but a riding buddy of mine used the same system for transporting his trials bike from Rockhampton (Queeensland) to Brisbane (Queensland) (650km each way) for trials competitions through the late 1990s. He used a Yamaha Super Tenere XTZ660 and had it set up well with communications (CB radio, phone and stereo).

I sometimes suggest to young people that they should get a job and earn squillions of dollars using their knowledge while they still know everything (before they get older and forget it all)

Replicas of the standard mounts but made in stainless steel are available from Fred and Debs KT Parts in New Zealand (and lots of other good stuff for KTs)

The reason why the condenser may be the problem is that you are checking the ignition timing by measuring when the points open, while the timing of the spark at the plug can be quite different to when the points open if the condenser is not working. Reasons for why the motor may not be sucking enough air are most commonly the rubber tube between the carby and barrel gets a split, crankshaft seals leaking or blown cylinder base gasket.

Is the fuel in the float bowl getting mixed with the incoming air? You haven't said if the plug is getting wet or not. If the plug isn't getting wet by you trying to start it, then the fuel is not getting mixed with the incoming air. You also didn't mention checking the pilot air passage for a blockage (old filter foam maybe).

Here is a brochure gallery that may help you ID your 349 http://www.southwestmontesa.com/gallery.html

I agree with mattylad about the monoshock OSSA and I would also allow Mick Andrew's 1973 works cantilever monoshock trials bike in Twinshock class, on the same basis. The Yamaha cantilever rear end was obviously found wanting because the frame was later modified to a twinshock rear end. Like the Yamaha works bike, the OSSA cantilever suspension was a design dead end. Both would be quite inferior to most of the twinshock bikes commonly seen in competition nowadays - and should be warmly welcomed into twinshock competition.

I see the bike you are talking about now. We didn't get that model here but it looks just like the XT350 we did get till about 1984. Yes the XT400 motor is way too tall to fit in the TY250 frame.

There is no XT400. The bloke in France modified an XT500 to look like a trials bike. An XT500 motor will not come anywhere near fitting in the space of the TY250 motor. Run a tape measure over a few 4 stroke motors (mainly the height of the motor but also the length) and compare them to the TY250 motor you will see what I'm on about. A TTR125 motor would come close to fitting (with reduced ground clearance) but I suspect you are after something bigger.

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 ?