DT125R FORUM

The first people with a 170 kit lifted the cylinder 3mm, hence the terrible torque curve..but from then on the myth that the 170 kit needed 'port adjustment' was set in stone..while it benefits from porting, lifting the whole lot 3mm is a bad idea...The Athena 170 cylinder is the same casting as the 125 but bored out to 65mm. Most people reported a good increase in bottom end grunt but no real gain at peak hp. It turns out this is mainly due to the cylinder casting being the same as their 125cc cylinder, so has 125cc sized ports.
I opened them up to 170cc sized ports by widening the exhaust
5mm, and lifting the transfers 1mm using a 1mm base spacer
and 1mm skimmed of the top of cylinder. It is better raising the
cylinder rather than modify the transfer ports as the Nicasil
plating chips easily.

Double check the pv cable setting. On mine with the pulley
lined up with the mark, it was only about 3/4 open. Only when
I looked up the port did I spot why it felt so flat initially!
Initially the 170 kit felt awful, until I double checked the pv
setting and found it was about 3mm closed. Once that was
reset, it flew...

Here is a proper 2002 powervalve on the left and early type diamond powervalve on the right, if they were all diamond shape wouldn't have a rectangle in powervalve pully. Yamaha didn't make a 2003 they are 2002 models just registered later.

Only the older DT and TZR TDR had a diamond shaped end on the powervalve, all the later 3RM models all have a rectangle end that is an exact fit in the powervalve pully. If it is a 2003 with a diamond shaped end then it is not the original powervalve and probably not the original barrel either.

@d3cme I have a 2002 dtr imported from the isle of man, has the 3rm-20 cdi. Moved the reed switch about 6 inches just cut the insulation so could pull the 2 wires really out of the way. Mine didn't rev past 7-8000 max till moved the reed switch now revs past 11000 and goes off the clock. If you rev it stood still in neutral does it got to 11000.

Added this tilt sensor to my alarm as can set it up easily with bike on the side stand so goes off if the bike moves less than 1mm.
https://www.ebay.co.uk/itm/Tilt-Switch-module-sensor-for-security-applications-motorbike-caravan-alarm/283171094902?hash=item41ee500176:g:bq4AAOSwawBbYKty

This is the alarm I have fitted, excellent alarm for the money and very loud.
https://www.ebay.co.uk/itm/EASY-FIT-Motorcycle-Motorbike-bike-Scooter-Trike-Quad-Alarm-2-wire-connection/191021841479?hash=item2c79c9fc47:g:SdcAAOSwk4RcNMLs

I keep my DT outside till building a new garage, this is the ground anchor I use with a 16mm chain and never had any problems with bike outside for over a year. I use a cheap alarm with an additonal motion sensor that was an extra £5, will find the link for you. Very sensative tilt sensor but doesn't go off in the wind, tilt sensor fully adjustable.
https://www.ebay.co.uk/itm/Oxford-Brute-Force-Motorcycle-Scooter-Ground-Wall-Anchor-Bike-Sold-Secure-LK397/253702132696?epid=1205376285&hash=item3b11d353d8:g:OmgAAOSw6AlbNLUD

Previously fitted a PWK 32 carb to a 2003 dt and the carb is quite small pictured next to a Mikuni TM 30. Fitted it to a modified 2003 dt inlet manifold, throttle cable outer needs shortening by 30mm carb end and with a warm air filter rubber fits over.

Hi, was bored and honed by Mick Abbey to 137cc but still has rebores left.

@StuKing94 Stay away from it as not a 2001 and
not even any 2001 parts on it. Should be like this genuine 2001.
https://pasteboard.co/xC8SKugS9JKs.jpg
https://pasteboard.co/iITMEcb8cfsb.jpg

I've got my latest DT project outside till get round to starting on it but have no worries about being stolen, have 3 chains on it with largest chain on rear wheel through ground anchor.

@calum The first people with a 170 kit lifted the cylinder 3mm, hence the terrible torque curve..but from then on the myth that the 170 kit needed 'port adjustment' was set in stone...(while it benefits from porting, lifting the whole lot 3mm is a bad idea) The Athena 170 cylinder is exactly the same casting as the 125, but bored out more and the pv is spaced further away from the bore. double check the pv cable setting. On mine with the pulley lined up with the mark, it was only about 3/4 open. Only when I looked up the port did I spot why it felt so flat initially! Exhaust port width limit is 73% of the bore diameter with good rings (measured straight across). So 56mm bore is 41mm and the 65mm bore can be opened up to 47mm. Although in the interests of safety I've stuck with 45mm for now (70%), same as the standard RD350. Most people reported a good increase in bottom end grunt but no real gain at peak hp. It turns out this is mainly due to the cylinder casting being the same as their 125cc cylinder, so it has 125cc sized ports. I opened them up to 170cc sized ports by widening the exhaust 5mm, and lifting the transfers about 1mm.
Initially the 170 kit felt awful, until I double checked the pv setting and found the spool must have a different end for DT's, as even with the pulley lined up, it was about 3mm closed. Once that was reset, it flew... Mick Abbey said 30mm best carb
for ported 170 so fitted 30mm Koso-Pwk.

@Calum yes got the head but knackered and yes the porting is not much better than standard 3mb barrel. Got a 4FU barrel with powervalve and better porting but snapped ring ruined the nikasil plating so needs a sleeve or repair and replate.

@SpookDog Crazy your gasket problems as done loads of engines and every head gasket from cheap white ones in those cheapo full gasket sets to athena gaskets and never had a problem. On barrels always use blowtorch on studs and 40 years working on 2 stroke engines and never snapped a stud yet. Remove studs then piece of glass with 240 wet & dry on barrel and head and 100% flat, I use my cooker hob as it glass really strong and it
doesn,t move about, just do mine when the wife is out.lol

@SpookDog Your previous barrel must of been worn out and lack
of power if think 3MB00P has more power as so mildly ported, the
P stamped parts had slighty more power as had different carbs etc. The P stamped head is standard 3MB head just without the casting numbers on top..

@calum Will be getting it dynoed at Mick Abbeys in a couple of weeks so will upload dyno results and video of its power run once
sorted. cheers Terry

@arild Added boost ports and modified powervalve to suit, can
upload port maps to add boostports.

HI @Oisin , not running a battery for the powervalve, a lot of years ago we just
fitted a pedal bike brake lever on the handlebars with some brake cables to the powervalve. That way we could adjust it easily for more top or bottom end with
no electics.

@valtteri Within a band of 2000 RPM centered around their resonant RPM they serve to absorb and give back pressure. When the intake port or reed valve closes there is a pressure created by the sudden stopping of the fuel/air flow from the carb. Some of that pressure enters the boost bottle and then exits back in perfect harmony with the intake opening at the YEIS systems resonant RPM. At all other RPM it does so with less force the farther away the RPM is from the systems resonance.

The YEIS is one of the ideal mechanisms that permit improvements of performance and fuel economy in the low and medium speed, part throttle operation of the two-stroke engine."
Pressure variation in the intake tract is more at low RPM than it is at high RPM, therefore the effect of the YEIS is much less at high RPM. Also it has more effect at partial throttle than at full throttle because the pressure variations in the intake manifold are more at partial throttle.

So running both bottles actualy gain in Hp at the bottom end, on race Tzrs etc they are blocked off as do nothing for top end power but disrupt the fuel flow through the inlet tract. You can actualy gain about 1hp drilling the hole larger on the bottle on top of the inlet manifold, drill the hole in the bottle 2mm larger than the diameter of the hole then swill out the bottle with petrol.

Single brown wire is front indicator.