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Alan.Tdm
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My newly restored Dt 125 LC 1 is down on power ie not pulling fully in top gear. I’m going through the list of possible causes. One could be a weakened spark. I’ve been told that the  igntion coil (flywheel) can degrade with age ? I know the compression/ fuelling/ sprocket ratios are okay. I will clean the front exhaust expansion chamber but it does not seem blocked

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Down on power is a very open statement.

Can you explain it in a more detailed way with some kind of reference.

"Top speed on a flat is 45mph and chokes on WOT." For example.

For all i know you could weigh 22stone. On some 125 bikes a flappy jacket or a mild headwind will render top all but useless.

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The bike is a DT125  LC 1. At the moment top speed is about 50/55 mph and ‘bogs down’ in top gear on the road. I only rev it to 6 k as still running in. The engine has been fully rebuilt so compression is okay plus seals. I’ve rebuilt the carb and cleaned the fuel supply. Also fitted new reed valves. New sprockets are the correct ratios. The front expansion chamber may be partially carboned up which I can check. The bike was running fine when it was last on the road 20 yrs ago. I read that the igntion coil can degrade with time although the resistance values are in range ?

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50/55mph at 6k is pretty good I reckon. 

Don't be afraid of taking it above that rpm while running in, just don't hold it there for long. The top end on my DT is at like 11500rpm, and I wouldn't put it in top gear until about 9000 minimum.

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Know how far i rode my tdr running it in at under 6k....?

NOWHERE. All that running in rubbish is cobblers. 

I did a steady trip to my mums ( under 10 miles) to be sure nothing fell off, leaked. Then rode normally. Avoid really hanging on the throttle or brutal down changes for a bit. Otherwise just use it.

That bore will do 15k tops before being done. How much longer will you get chugging around at 6k.

I bet less. You could even glaze the bore with modern oil and lose performance.

Its a smoker mate. Av it.

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Recommendation from the engine rebuilder who said take it easy for first 100 miles. Top gear is waste of time at the moment as engine has not got enough power to drive top gear. However there is a local company that can test the whole igntion system components so I’ll check this route out 

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Before going down that route stop being a big Jesse and open it up! 

Going in to top is pointless unless you're doing high rpm. So grab a handful and give it some :lol:

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  • 1 month later...
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Nice one, glad its fixed. People hardly ever come back and say what the problem actually was thanks.

 

Have you nailed it yet, eh?? :bad-boy:

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Well done,   i was thinkn the same,,,[ as cynic& finners]   coz i rode  aprilla125 ,  last year,, and it was ahoot above 7k,  ,  and flat below that ,, it was faster than my DT400,  [ NOT BOTTOM END ].    .

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yep, A freind had an Apprilia 125, she came round to my house saying it didn't sound right, no power.

 

I tried it with choke and it ran worse. so I blipped the throttle to wide open and managed to red line it and all the crap came out.

She the bike below 6k and basically the poor bike was 4 stroking. as it could'nt burn the fuel.

Now she guns it everywhere :D

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