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.

@Lukas55 Lukas55 the piston shouldn't hit the valve what ever position it's in. The piston normally won't normally touch the valve unless your barrel has been re bored 57mm or more. And then you need to grind the valve down to create clearance.
In that pic you've just posted the plastic pulley is how it's supposed to be with the valve completely open. If you look up the exhuast port it should be more or less level all the way to the piston. If it is like that with the pulley in that position that parts set correct.
Then it's a case of making sure the valves in the correct position for what ever revs the engines doing.

@SpookDog I think it's the angle of the pics that's making the valve look more closed than it is. As if you look at the edge of the powervalve nearest the exhaust it looks close to level with the surface of the exhaust port.

@Lukas55 removing the exhaust is the best way to check it 100%. You could always mark the power valve pulley and housing, with some paint or similar, while you have the exhaust off and the valves in the fully open position. That'll save you having to keep removing the exhaust to check. Just make sure you turn the engine off with the key switch once it's revved above 7k rpm.

Best way of checking the valve is open when it should be, is to rev the bike over 7k. Then turn the ignition off (while it's above 7k). Then check the position of the valve. From what I've heard on here, different years operate the cleaning cycle etc of the valve differently.
If it's revving out fine in fifth. It might just be down to a not 100% healthy engine not having the power to pull 6th gear well.

Does it rev higher in the other gears? The powervalve looks ok.

@Lukas55 yours looks to have a earlier cdi which are considered the best.

@Lukas55 the powervalve seems to operate as expected. It'd be worth taking the exhaust off to see if the valve is in the open position when it's supposed to be. It can be fitted 180° out. And to check there's no restrict ions in the exhuast it self.

@Lukas55 the black green wire comes from the cdi, but your bike will not have the black green wire. It's only found on later bikes 2004/5 onwards. I've got a feeling yours is running about 1998 wiring and cdi. The restrictions in the exhaust are in the front expansion chamber part.

@Lukas55 bitsa = bike made up from parts from several different bikes.
It sounds like your bike might have early wiring and cdi. I'd be checking the powervalve is in the open position and the exhaust has had the restrictions removed if it's a original yamaha one. Hard to make out much out from your pics.

@Lukas55 you first need to work out what model of dtr you have, it looks like it could be a bitsa'. Be worth looking to see what markings are on the cdi and wether it has a 3 or 5 wire power valve servo.