QuestionHi.
I am 99% finished (in conjunction with a small motorcycle repair shop) restoring a 1975 DT400B.
Problem being is we took it for first test ride and could not pull over 5000rpm. Kicks over and starts okay (3-4 kicks when cold) idles fine at 1-1500rpm. Has oil injection pump fitted. When in neutral, it revs quite freely and revs well past 5000rpm with no misfire or anything. Ride it, and it pulls away fine. Smooth up to about 3000rpm then starts to gradually.. become rough in its sound and feel up to 5000rpm and it seems to struggle to just get past that (5500-5800rpm)its like its run out of puff. I have new fuel tap, runs out freely, tank was professionally resprayed, kreme-coated inside and so on.
Repairman seems to think its electrical though he doesent exactly know what (could be this could be that scenario....) i'm not too sure... i told him timing needs to be exact and it is crucial. He says he has had a look and a play and has a strobe etc and all seems good..
I dont feel happy in his diagnosis. I live in Tropical Cairns, Australia and dealers/repairmen are limited!!
Please, any ideas to help us? The bike looks fantastic, cost me a fortune to redo but runs like a bag of spanners.
Incidently, it had a full top end rebuild (bottom end fine according to repairman) fitted with Wiseco piston/new rings/small ends etc)Its sounds sweet at idle and when lightish revving whilst in neutral.
Any ideas would be so appreciated!!
Yours sincerely, Mark Fairbank. P.S. I have a U.K. Haynes worksop manual for this bike and it dosent cover too much faults/settings.
AnswerMark,
-have you checked the plug color after a run?
Is it black? Is the air filter oily or fairly
clean?
-Inability to rev out could be a plugged
exhaust system, you can compensate a bit
with a smaller main jet in the carb.
-You don't want to lean it out too much or
you may burn a hole in that new piston.
-The pipe would need to be cut open and
cleaned/rewelded if that is the problem.
-try one size smaller main jet and see if it helps.
