feetupfun

The things that sounded a bit dodgy to me in your story are that: TY backing plates don't normally have slotted holes (maybe yours has been modded or is from a different bike). There is an ideal range for points gap that has nothing to do with the capacity of the motor. It is chosen to give the best spark. For Yamaha motors/ignitions like yours the ideal gap range is 0.3mm to 0.4mm, and you should be able to get the timing right without going outside that range. If the backing plate is moved too far away from the ideal position in either direction, the flywheel magnets won't be in the right spot relative to the ignition coil when the points open (causing weak spark). I suggest you set the timing from first principles ie using piston position and measuring the advance when the points open and also make sure the backing plate is in the right spot. If you have a picture showing the position of the backing plate on a standard TY250 you could probably get yours close enough to the right spot to eliminate that as a possible issue. To start with I would try somewhere between 2 mm and 1 mm BTDC with that motor. The ideal clearance for the coil laminations is as close as you can get without anything touching. If your bike has been sitting around for a while it is possible that there is now a bit of movement in the crankshaft bearings which could have caused the magnets to hit the laminations and maybe even loosen them and the flywheel. It would be pretty unusual for the not-revving issue to be caused by the timing being set a bit too far either way. Much more likely to be: Blockage somewhere (air inlet/filter, exhaust pipe/muffler, carbon buildup in exhaust port/ inside head) Worn rings Broken or bent reed/s Something wrong in the carby (some OEM TY carbys have an o-ring that seals the main jet into the needle jet and when this o-ring leaks, the bike will run very rich above low throttle openings)

Suggest you have a look at www.trials.com.au

What a strange question The internal flow resistance of the motor will limit the RPM to well within the mechanical strength limits of the motor. A standard 315 motor with throttle held open in neutral may rev up to 8000 - 9000 RPM. The upper end of the useful power range is probably around 6000 RPM.

Problem solved. I found a small pine leaf/ needle in my carb. It is amazing what you sometimes find in there. It's easy to get stuff into your float bowl. It can fall into the fuel line downstream of the filter when the hose is off the carby. It can get in via the air intake when you are cleaning the air filter. If you are really clever you can get it in through a float bowl vent line using a high pressure washer or compressed air. It can even fall in just as you are refitting the carby bowl. The most common pilot jet blockage item I've found is grass seed. Just the right size. The most common main jet blockage item I've seen would have to be water.

Zippy even if you do manage to get the bead to go up on the rim with high pressure, there are many people who have found that it will jump straight back off the rim when you let it down again to go riding. I have seen a novel approach recently using four tyre clamps that kept a tubeless tyre in place on a tube type rim not that I would recommend it though!

I haven't seen a bolt on kit for the TY250 TS from Millers. They do a bolt on kit for TY175 and they make a universal kit that requires you to make mounting plates. The B&J Racing TY250 TS kit is a bolt on and requires the original mounting lugs to be cut off. It comes with mounting plates and lowers the pegs about 25mm. Any lower and the underside of the pegs would be below the frame. There is a good photo of them mounted on a bike on their website.

Woody's suggestions about the clutch cable and arm length will make a big difference compared with standard equipment. Also make sure you have a handlebar clutch lever with high mechanical advantage. The AMAL levers that would have been on the bike when new are good in this regard while some aftermarket and Japanese levers have less mechanical advantage. A further reduction in clutch pull is available by fitting Barnett clutch plates. Using these allows the clutch pressure plate spring preload to be run a lot lower than with the standard all-steel Bultaco clutch plates. Have a look at your clutch before you order them though as they may have been fitted to the bike already. They should be available through any decent motorcycle shop. Be careful not to gear your 325 too low. They do feel a bit fast in first until you get the motor running sweetly. Standard gearing with the motor purring nicely will not limit you in the tight stuff. A M92 that is not running sweetly however can be a bit of a handful in the tight stuff. Even when you get the clutch pull nice and light, the action has a wide engagement point that can take some getting used to after Jap twinshocks or modern bikes.

I used the electric carving knife to shape a seat foam. It worked really well till the motor overheated.

Why don't you practise balance point wheelies using the rear brake when standing on the 315R? Once you can do that, you will find it easy on a sitting-down type bike. If you are still determined to do sitting wheelies on the 315R, why not attach some grippy fabric or sandpaper to the rear guard with double sided tape to stop your pants slipping and attach a shaped piece of dense foam or expended polystyrene to fill the dip. To get the footbrake lever position to work, have you tried wearing some shoes that are more flexible to allow your foot to flex up higher?

After lots of attention to detail, EBC shoes work great in my MAR. As well as what Jay said to do with the shoe pivot, there are a couple of other things that will help maximise the contact area: 1 If the drum surface is at all grooved, it will take ages to bed in the new linings. Taking a skim in a lathe to give a true surface may be needed. 2 Some OSSA front backing plates hold the shoes a bit eccentric to the drum. If yours won't centre properly when you fit the wheel, you may need to enlarge the axle hole a bit. 3 You should radius any new linings to match the drum diameter. I usually do this by repeated cycles of riding-inspection-shaping-riding. As well as the contact area, a new, high quality, low friction cable and a lever assembly with a high leverage ratio both make a big difference. an Amal lever assembly works well for me on the MAR. There is nothing wrong per se with MAR front brakes. With careful setup they can be made as good as anything else of the era.

The IT175 from the first model IT175 (1977) onwards has a completely different cylinder stud pattern to the TY175. The spacing was made wider to fit a larger reed block than what was in the DT, MX and YZ 125s and 175s that were made at the same time as the TY175.

I'm told the Honda XR600 (aluminium) kickstart fits the TY250 twinshock and while the Gas Gas lever ends up a bit shorter than the original, the XR600 lever is slightly longer than the original but is still much lighter (and probably easier to find at the wreckers).

The points may need more attention than just spraying with WD40 through the hole. I suggest removing the flywheel and drying out everything properly and cleaning the points properly. WD40 is good for displacing water but can cause problems if left to dry on the points. You can judge if the ignition system is the problem by looking at the spark with the plug removed and resting on the head. It should be a light blue colour.

Rechroming finish is not always as good a finish as the originals ie not as smooth, not as round, not honed. However it probably depends on where you get them done. Where I live it is much cheaper to buy good second hand tubes than to rechrome and rechrome is cheaper than NOS. If you say where you live you may get some local advice on pricing and quality of finish.

You said you checked the handlebar bolts but have you checked the handlebar brace clamp bolts? My bike had that problem and it was one of the brace clamps moving on the bars.

These appear to be TY250N model Z spokes but the listing doesn't say if they are for front or rear wheel http://www.francetrialclassic.com/uk/famille/19/7.html David

Because you called yourself New Guy and didn't say where you lived, I'm going to make a wild guess that you are from the US of A. If so, you should be able to get Falcon brand shockies off the shelf for your A model from Bob Ginder at B&J Racing, Tennessee http://www.bjracing.com/

Options for reboring KT250s Wiseco Honda MT/CR 250 Elsinore piston - take care when fitting barrell till rings ends get above the rear ports. CR pistons have ring ends end at rear (KT has ring ends at front) but the CR ring ends miss the port holes once assembled. No barrell spacer needed. I've had one in my KT for a few years now with no problems. Suzuki TS250 pistons work OK too but require a spacer under the barrell as the gudgeon pin is lower than on the KT piston. David Lahey

Its a Yamaha TY250Z motor in a Yamaha TY250Z frame.

It might cause the clutch springs to sag prematurely being kept compressed It might cause the hydraulic piston seals to fail prematurely being kept under pressure

I thought I had better do the sums comparing the number of Sherpa Ts made vs Yamaha TY twinshocks. Totalling the quantities for every Bultaco trials model listed in "Historia de la Sherpa T", I was surprised to get the figure of 52,729 bikes. Far more than I had thought and in the same ballpark as for Yamaha TY twinshocks. The only reference I have for the quantity of TY twinshocks sold is from Mick Andrews column in a recent Classic Dirt Bike magazine where he referred to Yamaha selling 30,000 TYs per year from 1974 onwards (presumably for at least 3 years?)

I just checked the original airbox from my M198 and it looks different to what you have described for the M199B (ie side covers mount to frame, no three funnel shaped rubber things in the top) so didn't take photos.

It's not Swooshdave that picked you up on the bit about Bultacos being the world's most popular Vintage Trials bike. It was me. Popularity to me means the number sold. If you choose pre-1970 for "Vintage", the most popular trials bike was probably the Bultaco Sherpa T. If you choose pre-1983 for "Vintage"(to include all years of Sherpa T production) the most popular trials bike was the TY250 twinshock by a huge margin. If you include any twinshock trials bike ever made, again the TY250 twinshock is still the most popular by a huge margin. If popularity in current events is the criteria, the most popular bike is harder to identify. In Spain, Spanish bikes are the most popular while in the USA and here in Australia, Japanese bikes greatly outnumber Spanish bikes in competition use and I have no idea about what is the most popular bike in the UK but based on the numbers of different bikes advertised on eBay in the UK, Yamaha would probably be ahead there too. Bultaco Sherpa Ts certainly are wonderful trials bikes and I love mine to death, but I don't think they have been dominant in numbers since about 1970.

If the M199B airbox/sidecover arrangement is the same as M198, I can help with photos of the original airbox. If you want photos, please let me know and I will do them this weekend. David

1. If you use TY mono yokes in a twinshock TY/Majesty frame, the standard mono yoke steering stops reduce the steering (side to side) angle severely compared with the twinshock yokes. Can the stops be trimmed back or are they just fundatmentally different in how they aremade? From memory new stops are needed on the bottom yoke to get enough steering angle ie they can't be trimmed enough. I would need to look at my riding buddie's bike (TY175 with TY mono front end) to be sure though. 3. TY175 yokes are made from the same basic forging as TY250 twinshock yokes so it makes no difference what you start with if you are going to bore them out to suit 35mm or 36mm tubes. If the yokes are bored out, should they be angled and offset a minute amount to account for the mono axle offset vs. twins shock centered axle? Would the reduced trail be a noticeable issue? I don't know the answer because I haven't done what you are suggesting. Remember that it is not just the axle that is offset differently on the mono front end. The mono yoke tube clamps are further rearwards than the twinshock yoke tube clamps relative to the stem and may well have a different angular offset too. One thing is for certain - if you bore the twinshock yokes out while retaining the same hole centres, you will only be reducing the trail by the offset of the axle so won't be too far wrong. Didn't someone else say it worked well to use the twinshock yokes bored out?