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.

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.

@DtxPower Best jetting for Athena 170 is 300 main jet on the
standard Mikuni tm28 carb but with the powerjet blocked off. Just cut the rubber tube in half from the float chamber to the powerjet then block the 2 halves of the rubber tube with a couple of 5mm threaded bolts or similar.

@waale2004 Best jetting for Athena 170 is 300 main jet on the
Mikuni tm28 but with the powerjet blocked off. Just cut the
rubber tube in half from the float chamber to the powerjet then block the 2 halves of the rubber tube with a couple of 5mm threaded bolts or similar.

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...

@lllDennis Best jetting for Athena 170 is 300 main jet on the
Mikuni tm28 but with the powerjet blocked off. Just cut the
rubber tube in half from the float chamber to the powerjet then block the 2 halves of the rubber tube with a couple of 5mm threaded bolts or similar.

@lllDennis Two-stroke piston seizures are either thermal-related or lubrication-failure-related. That one appears to me to be lubrication in nature. Could be overly rich jetting that allowed liquid fuel to wash oil off of the piston skirt as the fuel comes through the transfer ports, causing a lubrication failure.
If you need a gearbox have a couple of complete low mileage boxes can do you cheap.

@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.

@arild said in Engine tuning/ bike build:

80 pounds to rebore the cylinder

£80 for a rebore is very expensive, Mick Abbey charges £25 for a
rebore and hone and postage abroad is only £10 as done a few
cylinders for overseas customers.

On my 2003 dt there a 3 grease nipples, 1 on swinging arm and 2
on the linkage bolts.

Hi, use a K135 main jet with a K38 slow jet for a mildly ported 125.

HI, ALL SOLD NOW..