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Yamaha Ty250 Modifications

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What have you been doing to prepare a standard machine for trials.

My only mod to date is to lower and move rearwards the footrests.

What else is worth doing?

Do the wiseco pistons for yz/dt/it fit the ty what code number do I look for?

Do Boysen have reeds for the ty if so what is the code?

What gearing are you using.

What carb jetting for a standard engine.

Many thanks for youb help

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On my 74 TY

I use boysen reeds, good change,

removed head gasket, used hi temp rtv to seal,

ported cylinder and modified head

removed the ring on the flywheel,

moved the pegs down and back

Suzuki front wheel

gearing 42x10

Use at times Yamaha rear hub with a Fantic

tubeless rim

modified upper triple tree to use pro taper bars

bars moved forward

Gas Gas Dellorto carbs, 25 or 26mm

jetting for 5,000 ft altitude

fork tubes 1/2 inch above the top triple tree

makes noticeable differance in turning

Bultaco muffler and stock rear

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Definatly get the sammy miller TY footpegs. Those stock ones are just useless!

Other than that, I think the TY came with reeds anyways. Put a good carb on it and put modern trials tires on it. Also remove the oil tank under the seat and make it so you just premix your fuel to save some lbs...

Other than that, well it prolly gets a big more expensive. But I like the stuff that amos did to his. Sounds like an awesome bike, but really modern. Does it meet vintage rules?


Bultaco muffler

Gawd, I hope you aren't using that club foot silencer on it, please tell me your talking about the header/midmuffler... :ph34r:

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Thanks for the info,

What did you do on the porting front and head mods?

I am looking for a more modern power delivery not the slow old girl of yesteryear.

Where your changes required as a result of altitude we are nearer 500mm above sea level.

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Here's pictures of my bike

Fred's bike

One thing that help's, is to remove the head gasket, clean the

surfaces, and use high temp silicone, torque and let sit 24 hours

before starting.

I machined the head, moved the squish band closer to the piston.

Cleaned up the ports, raised the exhaust about 1mm, knife edged

the transfer port lower edge from the crankcase.

Removing the band on the flywheel helps the motor rev quicker.

Boysen reeds really help.


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Lowered the footrests,

removed head gasket,

machined half the flywheel weight off,

narrowed the side cover after removing the oil tank,

put on a modified tailbox with same internal design as a shirty mono,

28mm dellorto.

stiffened forks by removing tight would coils by 3" or so.

It certainly is a lot friskyer now only needs some Boyesens.

Does any one have a code number for the late post 1975 engine.

I have bought a cheap culinder off of a DT 250 i will fit this in a few weeks to see the difference.

Thanks for your help.

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Did you check the port timing/heights (dt250) against the ty cylinder?

On my TY I moved the pegs down and back, also I modified the upper

triple clamps to use Gas Gas handle bar stands, the bars mount forward

about 1.25 in.

I've been using either a 25 or 26mm dellorto, been playing with slides,

won't run clean with a "40" cut away, using 60 or 70 cut aways.

Using a Uni filter, done away with the stock air filter box.

What kind of modification to the clutch side cover have you done?

Anyone know of aftermarket triple clamps for the TY?

Next on the list is electronic ignition, and then a big bore kit.


Wyoming homepage

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For the side cover I just made sure it followed the line of the frame on left hand side.

I cut an alloy plate to use as a seat with a 2mm foam top. I.e as narrow and low as possible.

I have not yet got the barrel it is still at my fathers, the specs give 22bhp as a pose to 16 for TY so it will be more powerful, wether the bottom end goes only time will tell.

There is a big bore kit on ebay at the moment.

The clutch side cover is just cut away to leave the circular flywheel cover so that it does not trap mud.

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