Yamaha TDR 125 - Oil / Fuel / Air mixtures?...

[Funkmeister_Smith]

Hello!

This is my first post on this forum so I apologise if I'm asking questions that have been answered before or waffling on or whatever!

What it is, I have recently bought a K reg Yamaha TDR 125 which needed a bit of attention to get it through its MOT.
Basically, the back-box on the exhaust had a couple of holes in it & the starter motor was knackered, but other than that it was in quite good condition (apart from a few stupid snapped bolts! ).

But anyway, I have replaced the starter motor & have fitted a new, universal back-box, but it now doesn't start! It was working fine before the new exhaust was fitted but now it just refuses to start & I was thinking maybe its the oil / fuel / air mixture thats causing the problem because it always was quite smokey anyway.

So basically, what I need to know is HOW to set these mixtures, as I do not have a manual for the bike and I have trawled the internet for info & searched for books but cannot find the info I need. I have found a few adjusting screws on the engine, but I don't want to twiddle around with them until I'm sure I know what they do!!

Any help would be GREATLY appreciated, and again I'm sorry if this is something really easy and has been explained umpteen times before, but I'm new to tinkering with bikes engines and I don't want to break it!!

Cheers!

[Funkmeister_Smith]

I forgot to add, I have tried unclipping the air filter which didn't help, and I've checked the spark plug and it does seem to be a bit dark, which I presume would mean I have too much oil going through? I am going to buy a new spark plug tomorrow anyway just in case its that & see what happens with it then!

Also, I don't suppose it would have anything to do with the fact that we had the front end lifted off the ground for a few days would it? (I had it tied up by the handlebars to the garage roof so I could work on it from underneath). It wouldn't have leaked oil or whatever into somewhere it shouldnt have?

Cheers again! Sorry I've babbled on loads!