Hi, been lurking on the forum a while, but finally got round to registering. Over last 6 months or so been returning a H reg dt125r to the road. It sailed through it's mot back in february, but the engine is currently apart, being rebuilt to bring it up to the standard of the rest of the bike. I also own a K-reg honda nsr125rk, so like my 2 strokes Will start a project thread when I get some photo's worth posting, John.

You normally check the squish by feeding a small length of solder down the spark plug hole, so the edge of the solder touches the edge of the bore. Then turning the engine over by hand then measuring the squashed end of the solder with a micrometer or similar. The squish on my dtr was 0.6mm when I bought it, which seems to be on the tight side.

From experience it tends to be running too lean that kills two strokes. Though a 2 stroke makes more power the leaner it runs. At 57mm you often have to modify the power valve for clearance. And the head gasket will need opening up. When the barrel 1st seized they might have replaced it with a 'good' second hand barrel that had already been taken out a few sizes.

If yours has got the reed switch in the speedo it wont have the black/green wire. Pretty sure fitting the zeel would do away with that restriction anyway.

Freshly powdercoated parts going back together

starting to look more like a bike again next to my nsr125rk

and after a little light offroading

Piston rings have a hard life in a 2 stroke travelling over the open ports. I've seen the pins that stop the rings rotating on the piston move, allowing the ring to spin and open end catch on a port. With it being under load at time it failed (going up a steep hill), I wouldn't be surprised if piston expanded due to heat build up and pinched the rings. May have been running on the lean side aswell.

@gilerasc125 at 57mm bore it could well be catching powervalve and/or head gasket. I'd whip the powervalve out and check for any witness marks.

Big chain and padlock gets my vote. Preferably chained, with the chain and lock away from the ground. Makes it harder to attack with a hammer or cutters. Also if you can lock the padlock to part of the bike (as well as both ends of the chain obviously), it prevents them manouvring it into a position it's easier for them to attack.
Yes determined theifs will still try, but I don't believe you should make it easy for them.

Delorto 34mm vhsa is supposed to give good gains, a Honda rs125 carb inlet will fit the carb and bolt straight on to nsr engine. But it mounts the carb at a different angle, so on mine I'm looking at making a angled adapter to use between.
Make sure you have the full power cdi and power valve controller. Earlier jc20 barrels had more aggressive porting but are very rare now, and run slightly different power valves. Nsr150 engine is basically the same engine and top end will swap over onto the nsr engine.

Big chain and padlock gets my vote. Preferably chained, with the chain and lock away from the ground. Makes it harder to attack with a hammer or cutters. Also if you can lock the padlock to part of the bike (as well as both ends of the chain obviously), it prevents them manouvring it into a position it's easier for them to attack.
Yes determined theifs will still try, but I don't believe you should make it easy for them.

I'm running 120/80/18 and 90/90/21 Avon road riders on my dt. They are a little pinched up on the narrow dt rims. My plan was to have slightly wider rims laced onto the hubs. Still handles much better than on off road knoblies lol.

@SouthWalesYammy inside the opening on the radiator. There's a slight raised ridge the rubber seal on the rad cap seals agains't. If the system can't pressurise there, the coolant will expand as it warms and flow straight to the over flow bottle.

@SouthWalesYammy is the area where the rad cap seals agains't sound? I had exactly same symtoms and in end traced it to corosion damage where the rad cap seal, seals against.

@Calum my dt is fitted with tapper bearings top and bottom with out modifications, tapper bearings are able to cope with greater loads so generally last longer.

@mhbikesnbits according to the Yamaha workshop manual for a 88 its 0.20 - 0.70mm (1mm max)

@Calum I thought that was the case, I'd be checking the powervalves carefully as I know on the Suzuki's there prone to failing and dropping the power valve into the cylinder, ouch!

It's a Suzuki rgv250 engine in these isn't it?

I managed to get branded roller swingarm bearings for about half the price of Yamaha ones, the bearing code will be on the side of the old bearings if you still have them.

It's not just dt's, all frames for off road style bikes, tend to be worth more in good shape with logbooks. They get crashed/bent, rot out, get stolen and vin numbers removed. Turned into field bikes and paperwork/number plates lost. So a frame with clean ID and freshly powder coated (not rotten) frame can be used to resurrect one of these rough/damaged bikes.