Exhaust restrictors (Front Pipe).
Speedo restriction (limits the revs when bike hits 60MPH).
Inlet manifold restricted.
Removing Exhaust restrictors
Removing the restrictors on a bike from '99 onwards is a bit more involved than for older model bikes.
The exhaust needs cutting in half at the largest place along the welding seem.
A Dremel is required to cut the two pieces of metal out of the exhaust. It then needs carefully welding back together. Remember to paint the welding seem afterwards to stop it rusting.
Removing Speedo Restriction
The speed is restricted by means of a reed switch which is mounted in the rear of the speedo. It tells the CDI when the bike reaches 60mph and stops the revs from increasing.
To remove the speedo restriction take off the headlamp cowl and pull out the spring clips holding the speedo in. Then unscrew the speedo cable and lift up the clock. You will see two things in the bottom of the clock casing. One is round and is the light bulb for the clock, the other is white and oblong. This is the reed switch and you carefully prise it out and tuck it to one side out of the clock. I suggest you put it in a bag and tuck it as far away as possible. Do not cut or disconnect it.
Modify Inlet Manifold
First you need to remove the carburettor (refer to Haynes Manual). To remove the inlet manifold, unscrew the 4 x 10MM bolts and gently remove the two-stroke oil feed pipe attached to the top of it. And either block the oil feed pipe with something small or just make sure it stays up in the air so no oil leaks out of it. You should now be able to remove the inlet manifold, although it may require a little help to un-stick the manifold gasket from the engine.
The square rubber piece attached to the inlet manifold (as shown in the photo) is designed to channel all the air/fuel mixture
to the tip of the reed valve block, restricting the flow. To remove this square piece, get a stanley knife and first cut it off flat with the
base. Next you need to carefully trim the flat surface so that you get a nice curved surface from the hole to the outside.
When i refitted mine, i used instant gasket paste to ensure a good seal on re-assembly.
Also: When re-assembling, block the hole in the large air bottle (the one that's got a screw holding it to the frame).
This is another item that's been fitted to newer DTR's to mess with the air flow. Ideally it would be better to find an older
model inlet pipe to replace the one (with the large hole in the left hand side) that's fitted between the airbox and the carburettor.
To block the air bottle hole on mine i've used duct tape over the hole (on the bottle)(because duct tape is strong) and refitted
the bottle hence blocking the hole. It seemed to have worked.
Make sure the bottle seals in the hole properly with the duct tape on it. I put a square of duct tape over the hole with a strip all
the way round the edge to hold it in place.
And lastly on the inlet restrictions, remove the rubber snorkel off the top of the airbox under the seat. It'll help the air flow and
you'll hear the induction sound.
Please note:
If you are planning to do a lot of muddy, wet greenlaning/offroading then it would probably be best to leave the rubber snorkel on as it would stop the airbox from sucking loads of crap into it.