So here we are 3 years after i bought this bike.
The lad i bought this off is a member here and has been doing his new to him DT3.
I want this bang on.
So the story starts and through a chance meet with a guy called Dave Higgs, i now know a woman who does vapour blasting as a way of making a few bob. She lives less than a mile away. So getting stuff blasted now is a quick walk round to her house . She does loads of stuff.
I have read loads on what people use to strip paint off the body work and how useless stripper is.
Here's a simple solution.
A 20 litre chemical container with the top cut off and go to a shop that sells cheap thinners by the gallon. I paid £14.95 for 5 ltr
i bought 20 ltr. put all the tin wear in the container ,then covered it with the thinners.
Put a refuse bag over the top and taped it on to stop evaporation.
Left it over night and removed the tins this morning. Total of 4hrs going to get the thinners and sorting everything out and pouring the thinners back away. See the pic attached. Just brushed everything away. It was harder removing the tank stickers which are impervious to thinners and that took a couple of hrs. Stanley knife blade sorted that apart from where the dents are.
No sweat involved or compromise of the surface with blast media.
Next Evaporust! My favourite. Chemicals are the way forward like .

This some good info.. as my oil tank is gnarly... After this Holiday W/E here, I'll get my tank in for a bath... Was going to do electrolysis... 
Sneezles61

Hi Sneezles61.
I have treated this tank on the inside to electrolysis to.
That was before i discovered Evaporust on this here forum. However i will be using Evaporust inside this one . It's just no faffing .Pour it in and leave it. Job done. Then treat it afterwards.
One thing to point out here though. I have done an experiment with Evaporust. I treated a rusty old tool kit box by this method last year. I let it air dry without washing Evaporust off. It still has no rust on it a year later . It's not doused in fuel though. That's how good that stuff is . I'm a true advocate.

Thank you for yer thoughts.. I'll do more research.. Always looking for a simple, yet better way.. 
Sneezles61

I stripped the motor this morning and found the running problem.
I was right, it's the crank seal. The rings were partly stuck back too, the bottom one especially .
Plenty of carbon build up and it's way down the piston
 
 
Picked the frame up from the people i use for coating my stuff. I moaned because it was dear but i take it back as it's by far the best job they've done.
 

 Quick update.
I have used the lady from around the corner to aqua blast my parts. First rate job.
Now i have all the parts to rebuild my crank. I eventually bought genuine Yamaha parts still available through Fowlers Yamaha of Bristol here in the UK . Crank/rod shims, big and little end bearings, piston pin and clips.
I struggled getting the blanking plugs for the L/H case and put the part numbers in to E Bay. 
The 32 mm one turned up in the US and low and behold Fowlers for the 12mm ones The total cost of the plug from the states
was  £19.56p  for the two 12mm ones from Bristol £17.80 with postage.
So next is the crank and bore then rebuild.
One thing i would say is when i stripped this motor, i was amazed at how well it had been built. The barrel studs were locked in and in general i got the impression, this motor was built to be bullet proof.

 

I had the misfortune to break off one of the cylinder studs removing them. Was a hell of a job to get out. Sort of thing you don't want to have to do twice. Think someone had loctite'd them in unbeknown to me.

Sounds like you need this for the shop; www.etsy.com/listing/920630104/every-twe...te-job-is-one-broken

Hahaha, and that's so true Darinm !!!!

So ,here's a Yamaha brain teaser .
What don't you see in the post with the picture of the piston above in post #5 ?
Obviously if your none to familiar with the DT3 piston you won't know.
Okay d'ya give up then, or did you get fixated as i did on the stuck rings. 
Ready? I bought this bike with a running problem. The guy i bought it off was honest to tell me it had it.
I bought it through ebay of him and he's a forum member. There's nothing to say one little bit that he knew what that problem was or even if he had tried to find it. This is no reflection on him.
I found the spacer missing in the carb between the main jet and the needle jet. No, Wasn't that although it ran easier . Pinned it down to the crank seals . Gunge oozing out the gen side and it ran super on choke .
Now look at the next pics



With the low mileage on the bike and the age, i took a pitch at least it would need boring out to first over. 
When i got to the engineering shop ,i was talking with the machinist who i was in the middle of saying to " don't loose the piston as they're like rocking horse shit to find", at which point he dropped the new .25 piston straight through the bore  and out the other end !
"That will sound like a machine gun when you start that up with that piston in it, " he laughed.
Err hang on a bit .
You could have knocked me over with a feather. 
I shot off home to retrieve the piston i'd removed and the manual.
Returned to the machine shop.
He measured the bore and said that it was already 1.5mm over . He measured the bore and and piston and allowed the piston to cylinder wall clearance.
Christ only knows what the pistons from. Piston kit from Australia £179.00 plus postage  was the nearest rival  at .75 over but we both agreed that a re sleeve and standard piston would be better and only as expensive 
So i scurried of home and promptly found a new barrel with a good clean unmarked bore at

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.25 over  £65 fine English pounds from dk in Newcastle under Lyme Staffordshire.
Every cloud and all that guff.