My 2003 DTR has an aftermarket exhaust system, bigger main jet, the reed switch is removed and the inlet manifold restictor cut out.

So it is definitely derestricted and it flies through 1st 2nd 3rd and 4th but when I change to 5th it stops pulling

Any help would be greatly appreciated, I am just all out of ideas.

Ok we get this a LOT, so usual questions - how much do you weigh? - did you do the adjustments to the bike or did you get a "MATE" to do it for you? - what size sprockets do you have on it Front and Rear tooth count? - what fuel are you using? Tesco fuel is crap as is most of the cheap shit that superstores sell, are you using high octane non ethanol fuel? - there are so many things that can make your bike go slower than you want including "THAT'S HOW FAST IT GOES FFS!!!" Plus how fast did it go before or has it just started going slower? If the latter then you might have a problem with spark plug - ignition timing - fuel lines, shall I go on? you need to be a lot more specific about what it's doing before anyone can pin down the reason it's not doing what you want it to.

how many miles has the bike done?

Get a compression test done in the 1st instance Matt

the bike has about 5000 miles, I weigh about 70kg, sprockets etc are standard. Only mods to the bike are what I stated and I did them with the help of a guide.

It did 65 before as it was fully restricted and standard. I'm starting to suspect that the reed switch is the cause of this as it runs as it should until about 50ish, and I cannot find anything else wrong with the bike :/

So my next move is to replace it I guess Otherwise I will check the plug

TY for replying

I just want to say thanks to Airhead, I moved my powervalve as he shows in his DTR derestriction thread and it 100% fixed the problem. The bike is crazy now!

If you have any problems with your DT just go to this thread :