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

might also explain the markings in the bore

rest of the engine came apart pretty easy

I've had the crank rebuilt and barrel rebored, and have bought all new bearings for the engine. Just in need of a intact power valve cap and temperture sender (engine has the warning light type fitted). Then can start building the engine up, when I get some spare time. Also looking at fitting road tyres to the standard dtr wheels, if anyone has any recomendations on size and make? Cheers John.

Got a 1992 nsr myself, there well built bikes to be honest. Is yours the full faired version or naked F model? The most expensive part to fix on the engines is the barrel as its a plated barrel as standard, so can't be rebored. Mechanically there the same as the later foxeye nsr, so spares are pretty easy to come by. Done about 8k miles on mine over last couple years regularly doing 70-80 mile journey's. Will happily sit at 90 all day.

I must have the only dtr that's speedo under reads lol. I thought it felt quicker than speedo showed, checked speed at 30 with gps, showed actual speed was 33mph.

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.

@Calum said in H reg Dtr:

Yeah unfortunately that nut is connected to the output shaft

I wouldn't want to be hitting that with a hammer and chisel personally!!

Especially as that thing is going to be rotating at some silly speeds during operation.

With the nut drilled out, your only chiseling through about 1mm metal, with a nice sharp chisel it takes surprising little effort to split. Your tapping it rather than clouting it with a hammer.

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.

There is two parts to the generator on a dt and most bikes. There is charging coils that produce Ac current that the regulator/rectifier converts to 12v dc, to charge the battery. The 2nd is ignition coils which are used to produce a spark at the coil. Most bikes will run fine with out a battery, but with out the battery there to 'buffer' the voltage from the reg/rec you run the risk of voltage spikes so not recommended.
I presume the ignition switch interrupts the main power feed ( red and brown wires) and a feed to the ignition system, through the other two wires. I would see if the bike sparks with these other two wires (blue I think) disconnected at the ignition switch, but with the ignition on.

My understanding is the 1988 has the BN barrel and slightly longer stroke 0.5mm or something. 88 on wards they had slightly bigger bore and shorter stroke. Think if you mix and match parts you can end up with a 135cc or similar.

Is the clutch hub and basket lined up correctly seem to remember you can fit the dt one 4 different ways but will only work in one position

@Louis-James if its got the voltage reg already I should think it will. Probably have 3 white wires going to the vr and one red. The red is the 12v positive output that would go to the battery.

Those compression ratio's are both probably un corrected values, hence so high. The 'true' or corrected CR is worked out from the stroke once the piston has covered the ports, when your truly compressing the mixture. Not from bdc.

Or take the spacer tube out the standard fork, cut a piece of pvc pipe abit longer than the original and refit. Gives you more preload on the springs, so doesn't dive so much under heavy braking. And costs pennys to try first.

Probably the cheapest option but I've no idea what the quality of them is like.

@irongamer727 said in Opinions Honda NSR 125 1989:

@dtr-nsr soldering plastic? U mean melting the plastic together?

Yeah that's it, found it works best cleaning it back to bare plastic, then melting the two edges back together.

More mechanical advantage from a longer clutch activator arm maybe? Smoother cable routing?

Sounds like it's running lean at some point with choke improving things. You need to work out what throttle position the bog occurs and try richening up the part of the carb that controls that throttle position.

Its probably impossible to tell from the pics but there is a slight difference between the lips of the seal.

Didn't know if anyone had a rebuild pic showing the standard seal in position I could compare mine to

Which way round should the right crank seal be fitted? Haynes mentions the seal is marked 'outside' which should face towards the primary drive. But this being a patern seal from pjme isn't marked that way.

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.

You'd be lucky to get a uk frame with intact vin and log book for £100. I know of uk frames that have gone for £3-400. The extra hassle of it being a foreign frame will put people off, even if it's not a issue to sort. With it being freshly powder coated I wouldn't be surprised if you got £300 for it.

@declan I considered it even bought a rare dt80 engine to fit, then decided to buy a dtr instead lol

Be interesting to see, my first two bikes were dt50mx's, which I still own be it in bits lol.

Irongamer on here used to run the Athena kit so might be worth dropping him a message, for a good starting point.

There is two parts to the generator on a dt and most bikes. There is charging coils that produce Ac current that the regulator/rectifier converts to 12v dc, to charge the battery. The 2nd is ignition coils which are used to produce a spark at the coil. Most bikes will run fine with out a battery, but with out the battery there to 'buffer' the voltage from the reg/rec you run the risk of voltage spikes so not recommended.
I presume the ignition switch interrupts the main power feed ( red and brown wires) and a feed to the ignition system, through the other two wires. I would see if the bike sparks with these other two wires (blue I think) disconnected at the ignition switch, but with the ignition on.

I've got a feeling the kill switch makes connection, grounding a wire to kill the engine. If you've got the two kill switch wires shorted together, that would be like having the kill switch in 'off' position. Also my dt will spark once or twice with kill switch in off position.

My understanding is the 1988 has the BN barrel and slightly longer stroke 0.5mm or something. 88 on wards they had slightly bigger bore and shorter stroke. Think if you mix and match parts you can end up with a 135cc or similar.

Being a 88 won't it have the longer stroke crank? With that and oversized 3mb barrel probably gained quite a few cc's

Normally it's 3 white wires coming from the stator to voltage reg.

Probably the cheapest option but I've no idea what the quality of them is like.

If the speedo works I doubt it'll be the cable, sounds like the speedo unit has suffered some damage, probably easiest to replace speedo unit unless you can find another spares one to cannibalize for parts.

I may have one, stripped all the starter motor parts off my engine. Can have a look if you want?

More mechanical advantage from a longer clutch activator arm maybe? Smoother cable routing?

I believe there expensive due to being a oddball size, something .5mm wide I think.

Tyre size? My speedo under reads 3mph of actual speed, due to different size tyre, if you factor in most speedos over read. Could be 6mph+ difference.

Sounds like it's running lean at some point with choke improving things. You need to work out what throttle position the bog occurs and try richening up the part of the carb that controls that throttle position.

I'd check you've got a healthy spark kicking it over with kill switch set to run. Does sound electrical with it being connected with touching switch.

I'd say the pressure noise would be the plug igniting fuel in cylinder, noticed on my dtr it would produce a weak spark couple times after kill switch was set to off.

Is the clutch hub and basket lined up correctly seem to remember you can fit the dt one 4 different ways but will only work in one position

Hard to tell in the pic but looks like the gudgeon pin circlip is missing? Unless you took it out before pic.

Looks like your missing a bolt from the crank cases near inlet though.

Pretty sure there different where the oil pump mounts no?

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.

@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.

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.

When you say it has compression is that with a gauge or just thumb over plug hole? A mates bike had very similar symptoms, could feel compression with your thumb, gauge only showed 25psi though. On taking barrel off piston rings were in pieces and barrel heavily scored. Amazed it even had 25psi!

@Louis-James if its got the voltage reg already I should think it will. Probably have 3 white wires going to the vr and one red. The red is the 12v positive output that would go to the battery.

@Louis-James does it have the three white wires coming from the stator? You'd need them and a voltage regulator to convert the output from ac to dc.

I've always used loctite 2700 when fitting head studs to a barrel, as per my official Honda nsr manual.

Or take the spacer tube out the standard fork, cut a piece of pvc pipe abit longer than the original and refit. Gives you more preload on the springs, so doesn't dive so much under heavy braking. And costs pennys to try first.

That's just the carb slide stop screw hole, if there wasn't one already fitted the other side, so that wont be your issue.

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.

On my jc20 with the rs inlet the carb fouls on the regulator bracket. You might not have that problem on your jc22, but I think I worked the angel difference out to be 45* so it's quite a big difference.

I managed to buy a brand new rs125 inlet off ebay wasn't cheap though. The rs125 inlet fits perfectly into the nsr125 reed cage, so probably ran the same part. The rs125 barrel does look like it may fit. But not heard of one being fitted. I'm pretty sure a certain age of nsr250 barrel will fit, which may have better porting. The nsr250 was a v twin basically using two nsr125 barrels.

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.

Was that a euro lock by any chance?

Those compression ratio's are both probably un corrected values, hence so high. The 'true' or corrected CR is worked out from the stroke once the piston has covered the ports, when your truly compressing the mixture. Not from bdc.

Pretty sure the power jet isn't changeable on these carbs.

@calum said in Opinions Honda NSR 125 1989:

What's the powervalve setting on these?

There open at idle up to 2000rpm, then closes and starts re-opening at about 7500rpm. There's a hi and low mark on the power valve pulley you line up, but I've found like with dt your best checking up the exhaust port, to check there fully open. Some cdi and power valve controllers are restricted though.

I wouldn't say alot, but it noticeably improved with leaner jetting. Like you say power really comes in about 8krpm. Mine easily pulls to 80mph, you have to take it to the redline in 5th before changing into 6th and be well tucked in for it to pull in 6th I've found.

When I was running my nsr richer it was easy to start didn't even need choke. But since running it on leaner jetting it takes abit of tweaking but is loads livelier on the road.

I've found the jet upgrade kit dellorto sells, works well with the later barrel like yours will have. 138 main, 65 power and 42 idle jet.

Got the same exhaust on mine but with a tyga end can, what jetting are you running?

@irongamer727 said in Athena 170:

@calum I've already spent what I consider A LOT on this DT. Also have an NSR now. Ordered a stainless Romeu Henriques pipe for it. The DT is either way never going to be a performance machine. The Honda however..

What nsr did you end up getting irongamer727?

Same mechanically, some tend to be restricted in funny ways depending what country they originate from. Physically smaller than the jc20, easier to work on though as the fuel tank hinges up.

Would love a rs125 futura myself.

There's a spring/metal ring both sides of the seal.

Its probably impossible to tell from the pics but there is a slight difference between the lips of the seal.

Didn't know if anyone had a rebuild pic showing the standard seal in position I could compare mine to

Which way round should the right crank seal be fitted? Haynes mentions the seal is marked 'outside' which should face towards the primary drive. But this being a patern seal from pjme isn't marked that way.

You can bridge out the side stand relay to see if that or something else in the circuit is faulty.

The crm 125 uses the nsr125 engine. Having a nsr myself would have loved a crm. But was none forsale when I bought my dt, no regrets though.

Thanks for all the replies, the trailblazers definitely look promising for what I'm after. Cyber-ninja what inner tubes did you use with your trailblazers?

@Louis-James said in dtr road tyres:

For road only or trails, what style?

Just for road use, I'm thinking of having a second set of wheels to fit my knobblies to.

I'm not sure. I'm running the stock 21" and 18" wheels.

Has anyone got any recommendations for road tyres for stock dtr wheels? Also believe I've read some where on here a 120 width tyre will fit on the rear if anyone can confirm that? John.

@Calum said in H reg Dtr:

Yeah unfortunately that nut is connected to the output shaft

I wouldn't want to be hitting that with a hammer and chisel personally!!

Especially as that thing is going to be rotating at some silly speeds during operation.

With the nut drilled out, your only chiseling through about 1mm metal, with a nice sharp chisel it takes surprising little effort to split. Your tapping it rather than clouting it with a hammer.

Thanks Calum, will try to post as mush as possible! If this works, pic of my dt125r after a little light offroading.

![alt text]http://imgur.com/a/nCi4p(image url)

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.