feetupfun

Rob Welcome to the Oz twinshock trials fraternity. Great news. Does this mean you have given up the idea of getting a KTM trials bike? David

Neonsurge This problem never happened under acceleration hard or gentle. It was when the throttle was being closed and this is what BATRIAL seemed to be saying also. Yes a larger pilot jet will halp with pinging under acceleration but I don't think that is the problem here. David

Dear BATRIAL My 2003 REV3 200 used to make the same noise at the same time as what you described; just as the throttle is snapped shut. I tried different fuels, different jetting ie needle position, needle shape, pilot jet size, main jet size, float height, spark plug temperature rating and oil/fuel mix ratio. When I advanced the ignition timing a bit, the noise you described disappeared. The place where my bike runs so nicely is with the stator screws in the middle of the adjusting slots. In case there is confusion about what is advancing the ignition, it means to cause the spark to occur earlier ie to rotate the stator in the opposite direction to the direction the rotation of the rotor. I hope this is of use to you. David Lahey

Betas are known for sometimes developing corrosion that lets the coolant get into the gearbox oil. Have a close look inside the water pump cavity.

Chunky, If the red frame is original colour I would be guessing it a 1984 or 1985 model which would be called a TY250N here. I see the wheel rims are different colours. I suspect the rear wheel with gold rim is original and the non-standard front wheel has been fitted as part of the disc brake conversion. I don't know what bike the fuel tank is from. David

A photo would be pretty useful for identification.

Apart from reduced risk of melting ones wellies, can someone explain why reducing the temperature of the outside of the exhaust pipe on a 4 stroke is important? I would have thought that cooling the exhaust gas as quickly as possible to reduce its volume (by dissipating heat through the wall of the exhaust pipe) would mean the exhaust system could be made smaller diameter than if the exhaust gases were kept hot by coating the header with an insulator. Advocates of ceramic coated headers on trials bikes please share the reasons for doing it. By the way I'm not asking about turbocharged diesel truck headers because they are coated to keep as much heat (energy) in the exhaust gas as possible between the head and the turbo.

Mike The 51T rear will be fine but I suggest using a 12T front. Using 51/13 means that second is a bit too fast for most competition sections and first is a bit too fast for extremely tight stuff but OK for most sections. Using 51/12 is better for competition because it allows the choice of using first or second gears in sections and makes first nice and slow. The penalty is that a TY175 with 51/12 gearing will only do about 50-60km/h flat out so might be a little slow if you do much trail riding. David Lahey

Ishy what I see in your results is that: The outside temperature of an air cooled (4 stroke) motor is generally hotter than the outside of many water cooled (2 and 4 stroke) motors The water cooled motors had narrower operating temperature ranges than the air cooled motor (ie their thermostatic control systems were working) Both are totally expected results I would also expect that: If you tested an air cooled 2 stroke motor under the same conditions you would get a result similar to the Scorpa 125. If the ambient conditions of the test were very cold or very hot instead of the 30 degrees C, the benefits of water cooling would be even more apparent ie the water cooled bikes would have the same operating temperature range as for 30 degrees but the air cooled bikes would be correspondingly hotter in hotter weather and colder in colder conditions and would continue to see a wide temperature range at any given ambient conditions. BTW I'm assuming you did the testing in conditions considered hot in most of the trials riding world. In most of Australia the normal summertime day temperature is well above 30 degrees C. Where I live it is usually 33 in summer and 27 in winter. Further North and away from the coast summer days are normally around 43 degrees. This why I am an advocate of thermostatically controlled water cooled trials bikes be they 2 or 4 stroke.

Steve, is that Bundaberg, Queensland, Australia? Yes you are on the right track about the kicking it over compression. I have a M138 (350) Alpina which certainly warms you up kicking it over. If you are from this Bundy, there are well stocked Bultaco parts suppliers much closer than the UK ie Don and Marie Newell in Brisbane and Peter Schoene in Melbourne. Please reply if you want phone numbers. Sorry if you are from a non-OZ Bundaberg. From David Lahey, Gladstone (just up the road from the Bundaberg famous for Bundy Rum).

Is this a trick question? If they are your spoke nipples, why are you asking for someone else to tell you how big they are? More info please

What's the clutch slipping for? Yes fourth gear Yes feet on pegs If you are doing the wheelie on the flat, rest your backside up against the rear guard high enough to get your toe low enough to touch the brake pedal. If you are doing it uphill you can do without the rear brake. When you are ready, maintain mid RPM and feed out the clutch to get the front up. Starting speed can be almost stopped. The slower the better for starting as you will accelerate as you bring the front wheel up under power. As the front comes up, move you shoulders and head to one side so you can see where you are going, looking past the front wheel. The lower you sit, the more vertical the balance point will be. While the front wheel is still spinning you can get a strong steering effect by turning the bars opposite to the way you want the bike to turn. Old twinshock bikes with a higher centre of gravity are the best to learn on because they are less vertical at the balance point and have higher seats. This makes them easier to steer during the wheelie. Keep your torso and legs as still as possible. Some people prefer to hold the inner section of the bars or the top of the left fork leg with their left hand once the bike is up to get their arm out of their field of view.

In case you are still looking, there is a white Italjet 250 for sale in Australia. It has just been listed on the Australian Trials website. www.trials.com.au

Asking what is the best trials engine is a lot like asking someone "what is the world's coolest car?" It's so tempting to say "my car" But naming the worst trials engine is another thing altogether. For now I reckon the worst trials engine is simply the one that is not suited to the skill level of the rider using it.

Sounds a lot like an air leak. Check for air leaks at: The cylinder base gasket. The crank seals. Are they fitted the right way around? Are they the right type? The reed case to crankcase joint. The carby to reed case connecting piece. Did you take the throttle slide out to fit the carby to the bike? If so is the slide in backwards? Were the sealing surfaces of the crankcase halves OK? David

Hi BJ downunder. What you have pointed out about the difference in the finning design of 1970s two and four strokes is interesting but I'm not sure that it means that the two stroke has more problems keeping cool on a hot day (which we certainly get plenty of here down under). The main reason that 1970s Honda XL250 engines have less finning than air cooled two strokes of the same era is that it is all to do with surface area available for heat transfer. Because of the location of the cam, rocker gear and cam chain case inside the 1970s XL250 Honda engine, the external surface area of the engine available for heat transfer ends up almost large enough even without fins - hence stubby finning. In the case of a two stroke motor, the surface area of the head and cylinder without fins would be way too small. Hence a two stroke of the same power output as the XL250 would need more fin area. In reality the comparison between these two particular engines is problematic because the H6360 Monty motor would probably be able to produce about twice the power of a standard XL250 so there is a need for additional finning by comparison for that cause as well (waste heat produced increases with increased power output). Remember that the sizing of the cooling surface area is not only designed to prevent overheating, but also to prevent the engine getting too COLD in service.

My Cota 348 came with air valves on the fork caps. They are intended to be used as a tuning tool for fork action. The standard steel springs inside are a bit soft on their own. About 3psi with the forks topped out works fine for me as far as spring rate goes, but it does cause a bit of additional friction at the fork seals. If I could buy stiffer steel springs and run without the air pressure I would. Unfortunately I haven't found a replacement yet. BTW is your Cota really a 349 or is it a 348? They are quite different in the frame, engine, triple clamps and seat/tank. Where I live the 348 was sold 1976 to 1978 and the first red 349 came out in 1979. Keep on trying to get the front brakes to work well. Its worth it. The 348 has very good brakes when set up properly.

The measured weight of my Cota 348 ready to ride trials (no lights and half a tank of fuel) is 93kg. Others in the same stable also ready to ride are: TY250B 93kg KT250A2 94kg TY175B 83kg I would have hoped that a bike made 10 years after these bikes (the TLR250) would be lighter than a Cota 348.

Yes the Barnett fibre plates work great in Bultaco Sherpas. The takeup becomes silky smooth and the clutch spring preload can be backed off to provide a lighter pull yet retain the required resistance to slipping (they have a higher coefficient of friction than steel on steel). I just wish Barnett made them for Montesas as the sudden and jerky takeup is the main weakness with my 348 Cota in competition.

Honda RS is spot on as usual. Some people use loctite on the damper rod screws so an impact driver may not unscrew them if that is the case. The top end of the damper rod on the TY175 is definitely different to on the TY250 twinshock. From memory the TY175 damper rod top has a circular tip approx 12mm diameter with two flats milled off. A piece of steel tube flattened on two sides will do the job holding the damper rod and if you use a good light and look with the forks bottomed you will be able to see exactly what is needed. Paul McLeod's technique also sounds good for loctited screws and is probably less work than making a special tube spanner.

Just use a rattle gun (air driven impact socket driver) on those screws. It works great.

If your bike is revving its tits off and the kill switch won't stop the engine and you can't stop it by changing up gears and using the rear brake, inverting the whole bike (ie with it resting on top of handlebars and rear guard) will stop it very quickly. It works by lifting the main jet out of the fuel in the float bowl. This procedure has saved three trials bike engines that were sure to either seize or throw the rod but I was able to invert them in time. However there are a few risks: Starting a fire from any fuel that leaks out before the motor stops. Getting caught up in the chain or back wheel. Upsetting the owner by doing something unexpected to their pride and joy at a time of high stress.

Bruce Smith aged approx 19 years, member of my local trials club, accomplished trials rider, on his 1976 Sherpa riding along a 4wd track while out practising trials in 1978. He rode into the front of a bullbar-equipped 4WD at a relatively low speed and like 99% of trials riders at the time was not wearing a helmet. Bruce died due to the head injuries he sustained. I'm sure others know similar stories.

The main reason that TY250Zs were a sales failure here was the pricing. A 1994 TY250Z was $10,500AUS in 1994. At the same time the first model Beta Techno was $6,500AUS. The Yamaha did not seem to be a more competitive bike overall than the Techno despite some brilliant components. No wonder that only a few were taken up by privateers.

If anyone seriously wants a new TY250Z I've heard that there are a few brand new ones left here in Australia that were never able to be sold due to the ridiculously high ticket price at the time.