feetupfun

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?

DabDab I agree that it would be great to be able to buy lightweight WES exhausts for our Sherpa Ts but WES already do make exhausts for the world's most popular vintage trials bike. It's just that the Sherpa T isn't that bike.

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. 2. Yes the steering stems can be swapped to fit the mono yokes to a twinshock TY/Majesty frame. 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. 4. For people thinking about fitting Montesa, Bultaco or other Betor type forks to their TY/Majesty, carefully check the overall length to make sure the front of the bike ends up high enough because many of them are quite a bit shorter than the TY250 forks.

The local motorcycle shops here sell individual nipples and outer and inner of desired gauge by the metre. Cables made at home end up costing about $15 each this way. Alternatively their motorcycle mechanic will make custom cables for people at an hourly rate. Cables made this way cost about $40 each.

If you offset the forks or change their offset angle by altering the relationship of the triple clamp holes, you are changing the trail, not the rake. The rake angle is determined by the angle of the steering stem (steering axle), not the angle of the fork tubes. The factory MX teams alter the rake angle to tune the steering for a particular track by using eccentric bearing housings in the steering head. The easiest way to change the rake angle a lot (more than 1-2 degrees) is to do something like what Jay Lael has shown. Small adjustments can often be achieved by shockie length, fork tube height in triple clamps and spring preload front and rear but turning an oldish MX chassis into a Trials chassis normally requires some pretty serious frame work to get the steering nice.

Jays measurement will be correct only if there is no angular offset built into the triple clamps. Many bikes have this angular offset so beware.

Rake is the angle from vertical of the steering stem. It can be adjusted by changing the relative height of the front and rear of the bike (suspension settings or sliding the fork tubes in the clamps) or by using eccentric bearing seat inserts in the steering head or by cutting and welding the frame. Measuring the rake angle directly can be pretty tricky and is probably unnecessary. If you know how much you want to change the rake angle, the easiest way is to make an exact side view scale drawing of the bike then you can measure off the drawing how much you will need to change things (ie frame tube lengths) to achieve the change in rake angle you want. If you have access to modern drafting software it is possible to create drawings from photographs of structures.

Here in Australia all motorised vehicles (including trials bikes) are specifically excluded from my household contents and dwelling insurance policies. The only exception is for motorised wheelchairs.

$AU52 is a pretty normal price for a TY fuel tap. Those diamond shaped seals can be bought separately if that is all that is wrong with the tap. A better tap for TY250 and TY175 is the Kawasaki KT250 tap. About the same price but uses a different idea for sealing which lasts longer. No idea if a DT250 tap is the same as TY250A.

Mines a recently assembled Majesty using a NOS Godden frame kit and the running gear from a TY250D. Aluminium replica Majesty tank from France Trial Classic. 340mm Falcons with 60lb springs. Standard exhaust with new front pipe. The motor is currently a standard (250) except for the lightened flywheel. Photo from a recent club trial courtesy of Drew Wickerson

Dear zotz The 1974 TY250(A) has a seat with unusual construction. There is a moulded foam piece which usually goes so hard it feels like wood as you describe. There is a pressed steel base in there which by now is usually mostly iron oxide. The cover is stuck to the foam piece and hence inseperable. The seat is screwed to that wonderful fibreglass seat surround that gives the bike a very distinctive look. With a bit of persistence you should be able to buy a fibreglass replica seat base to suit the A model and take it from there yourself or take it to an automotive upholsterer with a good picture of what it looked like in 1974 to go by. Yamaha made some replacement seats for the TY250A and TY250B with plastic bases. I know only because there was one on a bike I bought with the part number sticker attached. I don't think they are available any more from Yamaha. There are complete new seats available for the C and D model TY250 but you will need a new, longer (C, D model) rear mudguard and some small mounting brackets added to your A model frame to make it fit. David

Yes that gearing is a bit high. I use 12/53 (428 chain) which is the same gearing as 10/44 and my first works well in tight stuff. Yes you will need second gear for climbing big banks.

1. If it idles, there is nothing wrong inside the motor so don't pull it apart again. 2. You haven't mentioned checking the fuel level in the float bowl. 3. You haven't mentioned checking that the reeds close properly. 4. Are you sure a rag or a wasp nest didn't get into the exhaust pipe while it was off? 5. Have you checked that the jet size stampings match the actual hole sizes?

Neo I'm not sure if this is any help, but the head of that REV3 bottom shock bolt is a precision fit into its hole so you have to get some penetrating lube to the side of the head as well as to the thread. The REV3 I worked on was three years old and that bolt had never been removed before. After a few days soaking it with Silkopen it came free without resorting to heating it. David

Yes I used air caps on my TY175 for a few years in the 1970s both with and without steel springs. You already are using air pressure as a spring in standard TY175 forks but with zero preload (atmospheric pressure). You can vary the overall spring rate to prevent bottoming by increasing your oil quantity if that is what you want. Careful measurement of oil height is required though to ensure the forks are getting full travel. Yes air caps "work" because: You can fiddle to your hearts content with spring rate and preload by varying oil quantity and gas pressure. However air caps are not used much in real life because: The gas heats up and cools down depending on ambient temperature and bike use and so changes your carefully adjusted pressures. The gas volume in TY175 forks is so small it is very hard to get the pressure where you want it. The increased pressure causes increased drag on the fork seals. This is not good for suspension action on a trials bike. For the same reason the fork seals wear out faster.

Ever since my TY 175 became 205cc, I have been breaking kickstart levers frequently. Yes they are easily available but it becomes expensive having to keep buying new ones. I have experimented with different home made designs but am not happy with any of them yet. The Mini Majesty featured on page 38 of Classic Dirt Bike Issue 2 (Ted Salmon's bike) has a kickstart lever that resembles the Yamaha item but looks a bit more substantial at the knuckle end than the Yamaha item. Maybe it's just an optical illusion in this case but does anyone know of where TY175 kickstart levers of a superior design are available from? Thanks

Steve Mine says 81 08 106 so I'm assuming made in August 1981 David