@CYBER-NINJA Thanks for the feedback Ninja!

To the OP, was the compressiontest done with a warm engine and open throttle?

As the lads have right said. 3BN fits but has a restictor, combustion ring, on it which is not good.

Avoid heads with pitting as they are no good. You want a nice head that has no pitting. If its sooty it can be polished but it's actually a known fact that sooty heads can actually increase performance, at the risk of reliability.

The soot acts as an insulator in the combustion chamber. Higher temps result in faster moving aor molecules. This gives a greater thrust onto the piston. But the excess heat can lead the engine into detonation, amongst other issues.

Personally, fascinating subject.

@britshgigolo Nope, nothing - I will probably investigate it further after christmas, i'm pretty busy atm - if I find a solution, I will of course share it here - in the meantime, if someone have a suggestion to a possible cause/solution, please let me know!

@CYBER-NINJA Thank you mate, appreciated.....forgot about them....now just to figure out where the pipes from the carb connect to....
Joys of buying a bike that's been "fixed" by previous owner....

@HOBO4LIFE Yep looks like a great price too

Can anybody tell me the thickness of the Cylinder head gasket? I don't have one to hand.

@MIGHTYMAN nah bud spot on.

@Calum Crap! I already did the modifications on the inlet manifold. I hope i didn't mess up my bike.
@Darty Thanks for your explanation! I will stop 'abusing' the reed valve stopper. I ordered the Boyesen dual stage reed valves so I wont need the stopper anymore. But like i said to Calum, I already did the modifications to the inlet manifold. Maybe I was a bit naif.
But I have read on 'scrimsmustangs' (when it was still online) that one of the restrictions on the 2001 bike is that 'square rubber nose' and that you had to cut off the whole part. So cutting away some parts seemed not so drastic as removing the whole part.

Sorry for not updating this thread but I was too busy riding haha
The seal change worked a treat but has flagged up a spark issue where I think the ht or wiring is earthing to frame intermittently
Could be ht or stand switch etc as its cutting out for a split second and then backfiring when the spark comes back 😞

@dtluke Yeah nice man.

No probs, happy to help 😬

Mine did this too when I bought it. I drained the oil in it and used rock oil lite lightweight gear oil and it slowly stopped doing it.

@AndyYam and yes, I really want a zeeltronic setup but they are quite pricey new and you don't see them second hand. Eventually I will

@dtluke To obtain part numbers and diagrams these 2 webby's are super useful;

https://www.fowlersparts.co.uk/browser/manufacturer/yamaha/bike/dt125r

https://www.yamahamotorcyclespares.co.uk/spares/choosemodel.asp?Make=YAMAHA&uID=0

Just pick your bikes year etc - HTH 😉

Best give him a ring really. Doubt he really checks his Facebook. He is a nice enough bloke you can ask him.

When I spoke to him he quoted 170 for barrel ported and head squishband and powervalve adjustments.

In order for him.to.do his work he needs the piston you are going to use, barrel and of course the head.

Thanks again. Will plug it up

Evening,

Just thought I'd let you know the bike is running sweet as a nut. Hadn't started in a day or 2 after it was idling at 3-4k. First kick this afternoon and it started and idles perfectly, it's mended itself!!

@Calum thanks, ordered one