2002 DT125R tops out at 60mph ?

  • This is one of those questions which gets asked a lot,but having read a thousand links (maybe not quite a thousand lol) I am still not 100% sure so where better to ask than the home of the DT 125 forum.
    So a little history of bike top end has been overhauled re-bore piston rings etc,Carburetor has a 240 jet in it, new airfilter and reed switch out of way bagged up and taped up, Exhaust is stock and not gutted but has a KMX 125 tail pipe fitted ( that;s how it came to me) . bike accelerates decently through gears and revs well upto 7000rpm in most gears but once it reaches 60 mph it just stays there 55 mph up hill. Is it the CDI or have I missed something.

  • @Leftyno1 Could be you need to go up a few teeth on the front sprocket possibly? Also check the silencer as one of my project dt's I'm building up was doing similar and it turned out the silencer was gunked up with crap and once changed the bike is a flying machine well over 70mph out it

  • Should rev hard to the red line pal.

    If it's not then there is something wrong.

    If it revs fine in the bottom end then it sounds like an exhaust issue. Or anything on the exhaust side.

    If not then it sounds like something else.

    First point of call. Pin the powervalve in the open position and take it for a test run

  • Ok will pin power valve and try it then get back to you,cheers

  • Well before doing power valve I thought I would take bike to the only straight piece of road on island 0.6 miles long (yes you read it right).
    So really revved in every gear to about 8500 rpm until changing gear and got bike up to 70 mph in 0,4 of a mile before having to hit brakes before road runs out at 0.6 of a mile ,so I was just not revving bike hard enough when I tried first time because still had my treat it gentle running in head on.
    There is no where on island to go any faster than that so I;m not going even gut the exhaust as what is the point . So going to leave bike as it is ,thanks for help.

  • Uhmm it's really bad for a two stroke to be ridden out of the power band. 8k is the minimum you need to be riding it mate. You will lug the engine riding it at low rpms. Oil will build up restricting the bike.

    Two strokes are designed to be ridden hard. Riding them softly is not ideal for them. Piston needs replacing every 10k miles. Engine rebuild on these by 30. May as well make the most of it.

    Open it up. You can cruise at low rpm. Provided there is literally no load on the engine. But if you're accelerating then be sure to be changing at like 10500rpm.

    It won't do it any harm riding it to 10k. It's not a four stroke.

  • point taken Calum, but speed limit on island is 25 mph ( which everyone seems to ignore lol ) but the roads are twisty ,potholed have gravel on corners sometimes and are up hill or down hill never straight so riding bike hard is not easy here and do not get me started on local driving skills like stopping to chat with someone on a blind corner, but totally agree that its not a 4 stroke so needs to rev a lot more now its run in, Cheers.

  • Oh yeah have to take it Easy when running it in. But once that's done you will want to use the whole rev range. Especially if it's quite heavy.

    See two stroke engines are naturally aspirated. But when the engine rpm reaches the resonance frequency of the exhaust system then the engine forces lost charge from the exhaust port back into the combustion chamber. Not only that but it will purge the transfer ports of fresh charge. In other words if you ain't in the power band then you are wasting fuel out the exhaust port and not reaching the engines volumetric efficiency.

    You put unnecessary load on the engine and waste fuel. Do you self a favour ride it like a two stroke.

  • Do any of you know what restrictions are on a 2002 dtr 125 that are easy enough to do ??