feetupfun

Sag 40%-50% with you on board and balanced fore/aft ie all weight on footpegs Set the fork tube ends level with the top of the top clamp and use 340mm shocks (also with 40% to 50% sag). TY250 steering is perfect when set up like this. You will lose precious ground clearance if you slide the tubes up in the clamps. 40lb springs will be too light if you weigh more than about 65kg

Some people take off the flywheel on the primary drive side of the 348s to make the motor a bit more snappy - I haven't Some people fit lower footpegs to 348s and 349s - I haven't Some people fit a better carby - I haven't - yet You might like stiffer fork springs unless you are light Electronic pointless ignition has recently become available, but the standard ignition works fine. Using very heavy oil in the clutch makes it smoother on engagement. I've heard that Honda 125 (CB,TL,MT,CR) clutch plates improve the clutch action. I have bought some of these plates but haven't tried them yet. If it has frames tubes under the motor, it is a 348

If you using both a 25mm nylon spacer and the standard yamaha spacer and are using standard yamaha springs, you will definitely be suffering coil-bind before the hydraulic anti-bottoming starts working. This means the forks will bottom with a bang and will have reduced stroke compared with standard forks. The oil level sounds fine.

The originals are alloy

Hi Newtotrials I'm also 50 and am 208lbs and 5'10" and have been riding my TY175 since 1976. I see you have already worked out that the forks are a bit soft. I tried many things over the years and was not happy with the forks till 5 years ago when I fitted TY250 twinshock forks. The slightly stiffer rate springs and reduced fork flex are a good improvement. If you want to try stiffer springs in the TY175 forks, those from a TM125 Suzuki will give you just that and there are probably other Jap dirt bikes of that same era that will have springs that will fit in the TY forks and be stiffer. The swingarm lengthening as previously mentioned is a good thing. The standard wheelbase is so short that stability is quite poor and riding up steep stuff takes quite a bit of concentration - especially turning up a steep bit from a cross-camber. The decision of what length shockies to get is really a personal one because it depends on if you are a stationary balance/hopping person, or a no-stop type rider. The extra clearance with the longer shocks helps with no-stop riding but stationary balance is worse. The Betors come standard with damping that is a bit stiff for best performance on things like loose rocks. They are good value though if you are not after the best at any cost. Theres nothing wrong with riding the bike with SM footpeg kits. They are a tiny bit lower and further back than standard. The overall width of the bike is increased and they are way more comfortable. The RH peg will need to be held up to use the standard kickstart lever. Theres no performance benefit with a SM tank - they don't give a weight saving over the standard setup and may even be heavier. They are useful though because many standard steel tanks have been lost to rust. Lightweight aluminium tanks are available for lots of $$$. Yes 50lb springs will be perfect you and yes it will upset the suspension balance a bit with the standard forks, but most people I ride with use this combination and love it all the same. David

Being the lightest available full-sized trials bike probably means that it isn't the strongest full-sized trials bike and maybe the suspension bottomed out more heavily that it was designed for?

Yes OEM Yamaha rears are no longer available from Yamaha. Yes you can get aftermarket 428 chain rears and fronts. What makes you think they will be cheaper than 520 sprockets? 428 and 520 sprockets from: www.bjracing.com www.tytrials.co.uk

I don't know but it is probably the same reason why wavy edge brake discs work well too. Don't complain, those clutches work fantastically. Note that the "nipples" are meant to line up with the arrows on the pressure plate and each successive plate goes in at 120 degrees from the previous one. The later model TY250 twinshocks have a slightly different clutch - on them all the steel plates are the same and the pressure plate works as the last inner plate.

If it is a MITAS 4.10 competition trials tyre, it will be slightly (~10mm) wider than a normal competition trials tyre and may rub on the chain guard on an M198/199. It will also have a non-ideal aspect ratio ie it will not have as much depth as a normal competition tyre. If it is a tubeless type (which the MITAS is), the bead may not stay on the seat when you let the pressure down for trials riding. For more info about the tyre you have been offered you will need to say what tyre it is (and don't expect a sane answer if you say you are thinking of putting a 4.10 knobby rear tyre on it). Any competition trials tyre that will fit your rim would be good for trail riding. The most likely ones to fit your bike are the Michelin tube type and the IRC tube type. The IRC is usually cheaper. For info on pressures you will need to say what sort of fun riding you do.

I use B6ES in my TY250A, B and D for trials competition If I was using it on the road I would use a B7ES

I think it is important to note here that Andy T lives in the UK while subanator and I live in parts of Australia that can get very hot. Some bikes that might never give a problem in cooler climes require heat shields to keep the carby cool when ridden here.

I think the red 99 also has Dougies name on it

Fork oil weight is a personal thing so 10WT might be fine for you and those springs. I use 20WT oil and run the level higher than the standard oil quantity provides (125mm below the top of the tubes with forks bottomed and springs removed) You should set the spring preload to suit whatever springs you fit so that the forks are at about 50% of their travel with you on board and with your weight only the footpegs. Take care not to use so much preload that the springs coils touch before the forks bottom (the more preload you give the springs, the smaller the gaps between the coils) Another thing is that by using solid spring spacers you are effectively reducing the air space inside the forks

Jaan the free length of a spring is not particularly important. The spring rate is determined by the other properties of the spring (number of active coils, coil diameter and wire diameter). The free length can change over time. Another thing about 348s is that there was a range of springs used in them so it is no surprise to me that what came out of your forks is different to what someone sold you for your bike. I have three sets of 348 forks and they all had different springs in them when I got them. Without meaning to confuse things further I have found that to get a high enough spring rate for my 348, I have used aftermarket springs made for TY250 twinshock forks.

Mate if you really want to know what Monty you have there, you will need to do a bit better describing it or post a photo somewhere so we can see it And Montesa has only one s (in your profile)

If you are asking about mine, the squish area in the head on mine was machined to make the OD of the combustion chamber the same diameter as the bore. That change combined with the bigger piston displacement changes the compression ratio, so the sealing surface was machined to bring the compression back close to but slightly higher than standard. No I don't remember how much was machined off the sealing surface and it would probably not be much use knowing anyway unless someone was to do one exactly the same big-bore job. No the timing works great at the standard setting but low RPM throttle response is more sensitive to the timing setting than before. I think an ignition with an advance curve would provide further benefits.

If the sleeve fits the standard crankcase mouth, it will be less than 200cc. Mine has a 72.5mm bore, very thin sleeve and the studs are just touching the OD of the sleeve. You don't machine the ports. You cut them by hand undersize before the sleeve is fitted, then enlarge them back to the right size with a porting tool to match the ports in the aluminium casting. That is the same with any new sleeve, big bore or standard. Yes raise the compression, fit a good electronic ignition, and lighten the flywheel a bit. If you go up in compression much though, don't lighten the flywheel as my standard flywheel is now a bit on the light side with the higher compression. You can machine the head for more compression without affecting the squish height by machining the squish area back as well as machining the sealing surface. Most people just run a very thin head gasket to get the compression up a bit. Yes I would agree that if you want to retain full reliability, then retain the standard sleeve. My sleeve is scary thin, and I don't expect to get the life from it that I would expect with a standard motor.

MITAS make a road-legal rear competition trials tyre that is much better for off-road use than the normal road-legal rear tyres, but it is made for tubeless rims. I have had one on my 348 rim but it took lots of perseverance to get ot to stay on at low pressure and I do not know if it will fit properly on a standard Yamaha rim. These MITAS tyres do wear lots better than IRC/Michelin/Dunlop comp tyres, but are lower profile so will always be a bit performance limited on edges (sharp rocks, slippery roots etc) compared with the favorites

I've been riding my 205cc TY175 since 2004. It is not the same conversion as John Cane or Craig Mawlem. It uses a piston made for big-boring the DT200/WR200 motor. It happens to have the right pin diameter and piston height to crown dimension that matches the TY175, so no barrel spacer or gudgeon pin bushes are needed. I use a standard carby, standard front exhaust with WES rear muffler and standard airbox arrangement and standard port and ignition timing. The barrell was resleeved bigger using a second hand Suzuki GS1000 sleeve. The cylinder head retaining stud holes were welded up and redrilled 8mm and plain 8mm nuts used hold it together. This was to provide for the increased ID of the head gasket hole. The head was machined to suit the bigger bore diameter and to provide slightly higher compression ratio than standard. The crankcases were machined out to suit the OD of the bigger sleeve. The flywheel is standard. The positives It runs fine and has more torque at all RPM than standard but only as much as you might expect with the extra 30cc. It is more responsive to throttle input (same flywheel and more power) The negatives It vibrates noticably (due to the increased mass of the bigger piston) It stalls easier It is easier to break the standard flimsy kickstart lever when starting it The motor mount bolts have to be removed and motor inclined to provide clearance to get the barrell on or off the (longer) studs.

If you are used to riding modern bikes, there may not be anything "wrong" with the TY mono. It will probably just be your perception of what a motor should respond like.

Why would you fit a one-way valve to a vent line when it needs to vent both ways? I know some tank vents have a device to stop fuel pouring out when the bike is upside down, but that is not a one-way valve.

The oil in the exhaust is because it is a two stroke and you are using oil that resists burning. Clean the muffler out and get used to doing it. Don't fiddle with the jetting if it works well within sections. Your problem sounds more like: Possibly might have too hot a sparkplug heat range for high speed work Possibly a part blocked fuel tank/float bowl venting system Possibly a crankcase air leak Possibly fuel supply blockage (tank valve filter?) Possibly old fuel Possibly carbon deposits on piston crown and inside head Keep your finger on the killswitch until the motor has stopped turning. It's only backfiring because you are effectively turning the ignition back on before it has completely stopped. How do you know you are getting reed flutter?

Unless you know the engine number that the barrel came off originally, no you can't date them any better. What does it matter what year it was made if they didn't change the design between C, D and E models? From memory here is a guide to the 493 models numbers: The unique engine number starts after the 493- . If the number starts with 1 that means C (1976) model. 2 is D (1977) and 3 is E (19??). Check out John Cane's guide here and see if I remembered it right! http://www.tytrials.co.uk/technicalarticles_302159.html I had problems fitting a Venhill KT250 clutch cable to my KT250. It was the first Venhill cable I tried and I haven't bought any more since and so haven't tried the Venhill clutch cable made for the TY250. Apart from the KT, my bikes have clutch cables made by myself with inner and outer bought from the local bike shop and from some imported universal clutch cable kits and they work great. While Yamaha front brake cables are available (in black) and are very good, Yamaha TY250 twinshock clutch cables are not available any more/yet.

What does your artistic mind say? I personally don't like the look of the fibreglass M159-tanked Sherpa T and do like the look of the plastic M198/199 type tank in both red and blue so for me it would be easy (thats why I got a M198 in the first place - because they look so cool) As far as longevity goes, the plastic tank will probably discolour over time and they can be tricky to make look good again with paint (which is probably why they are being made again 30 years after they were originally made). The fibreglass tank will be able to be repainted ad infinitem with ease, but will need to be lined with epoxy to protect it from the ethanol that will soon be in all our Aussie car fuels. I reckon the best Sherpa T tanks are the aluminium ones that were fitted to UK bikes. The older bulbous ones look especially good. The later ones that look like the plastic tanks are sensible and long lasting but don't really look any better than the plastic ones. It is a great debate

Oh well it was worth checking the barrells. Yes except it is the other way around. Opening the points gap makes the spark happen earlier.