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.

Welcome, your not too far away (NW Leicestershire), often over that way doing a little green Laning.

@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.

Tdr 250?

Ninja's friend is very much right, typically the bigger the air box the better. But a manufacturer can tweak the volume of the air box, to change its resonance, to help fill a flat spot in the rpm range. To make a engine more flexible, not something that important on a engine that will be running a full tilt most the time.

Most 'ram air' intakes are just cold air feeds, I believe the Yamaha thundercat was one of the first bikes to run a true ram air setup. And that is far more than just sealed air feeds to the airbox. It has various air chambers under the fairings, and even uses the air to pressurise the float bowls on the carbs to increase fueling to match. And with all that, it's claimed to only add 3hp at over 100mph, and that's on a near 100bhp engine.

Unless your trying to chase every last 0.5hp, I think your best off with a air box, especially on the street.

Those forks either have wrong parts fitted, missing parts or broken springs. Or any combination of the three lol

Welcome, your not too far away (NW Leicestershire), often over that way doing a little green Laning.

@calum yeah it certainly wasn't a happy piston, also was a dark heat spot on the underside of the crown.

Pictures of a dt piston that heat seized due to lean mixture, from the base gasket blowing. You can see the classic 4 point seize and a little detonation damage to the piston crown nearest the exhaust port. Believe it or not, pistons aren't perfectly round, And are normally narrower along the line of the gudgeon pin, so it would be very unlikely to get a heat seizure at that point on the piston.

@spookdog that's not a 4 point heat seizure from running lean though. The side of piston above the gudgeon pin see's very little load. Only time I've seen damage to the side of a piston similar, was when a gudgeon pin clip had come loose.

If it was only one side I'd say bent rod, what was the little end bearing like? And what does the plating look like near the transfer ports?

@karumaspt I may have miss understood what you've put, but sounds like mixing the parts might be causing your problems. I know some bikes have two pickups one for low rpm timing and one for high rpm. So joining the two would very likely cause issues.
And the impedance of the different year pickups could be different, causing them to burn out.
I'd try get one matching setup, all from the same year to remove those variables.

@arild I think they were 50mm longer than stock. That was for road use though, but did seem ok green Laning at the weekend.

I've fitted longer spacers in my front forks, which has made them stiffer. Much better for road use. With out, the front end used to dive a stupid amount under hard braking, often causing the rear to lock with the weight transfer (road tyres). And that was on freshly rebuilt forks.
Also not all grades of fork oil are equal, one brands 10w might be anothers 15w. Your best looking at the cst rating of the oil to compare them.