I bought a 1974 TY 175 about a month ago it had no spark, I have fitted electronic ignition.
So the only way I get it to run is to remove plug and pour some premix in and it will run very smokey until its burnt the petrol I've poured in then stop.
Does that mean its crank seals have gone and need replacing ?

Maybe the crank seals you need to check everything, air cleaner, exhaust, different spark plug.

On the TY175 carb an o ring is fitted around the main jet this goes into the float bowl, pull off the carb float bowl you will see what I mean, replace the o ring with one that is a good fit it clean the carb out. Good luck please let us know what you find.

My advice is - strip carb and have all parts ultrasonically cleaned, replace o rings with new, check float height = 21mm, reassemble, mixture screw setting 2.5 to 2.75 turns out.

Remove petrol tap from tank and clean, wash tank out with fresh fuel, reassemble, fit inline fuel filter.

If you use carb cleaner instead of ultra sonic, remove all o rings first, they don't like it.

I bought a 1974 TY 175 about a month ago it had no spark, I have fitted electronic ignition.

So the only way I get it to run is to remove plug and pour some premix in and it will run very smokey until its burnt the petrol I've poured in then stop.

Does that mean its crank seals have gone and need replacing ?

From no start to questioning your crank seals is a big jump.

I would clean the carb about a dozen times and make sure the reed valves are perfect before diving deeper into the engine.

While the carb is off, hold your hand over the intake manifold, turn the engine over slow and see if you have any intake vacuum.

Make sure your oil injection lines are all good or properly obsoleted.

If your intake vacuum pressure is low, it could just as easily be gummed up and stuck piston rings.

Edited September 16, 201411 yr by eota

Just skip it all. Take off the mag cover and grab the flywheel. Maybe the mains are shot in the first place. The crank bouncing in the mains create many problems.

Sounds like a fuel supply problem.

Start your investigation with the cheap and easy options -

Is petrol flowing from the tank?

Is the petrol in the tank fresh?

Is petrol reaching the carb?

Is there petrol in the float bowl?

Take the air filter out (only briefly for the test) to see if it then runs.

Thanks for all replies I have cleaned carb again put fresh petrol in and it runs OK still very smokey. Will have to put a chain and sprockets and see how it pulls as I have another 175 that I can change bits to try.

Going to try and make one good bike from two and try and alter frame etc as I also have spare frame. So its not going to be a 5 minute job.

Keep an eye on the gearbox oil, if its going down then its getting sucked past the crank seal. Could be why its Smokey.