Yamaha DT 125 R won?t start

[culpan]

Hi people,
I have recently bought myself a DT 125R 03 model but I am having trouble starting it. It is second hand with only 400 miles on the clock but the guy I bought it from had not used it for almost 3 months and has just been sat outside under a blanket.

For the first couple of days it was running ok and did a few miles to try and blow some of the crap out the exhaust (which landed on my shiny wheels) but it didn’t like being revved much nor did it go well in first or second gear.

Now it has given up all together it cut out on me for no reason yesterday, so the spark plug came out which was all oiled up so was cleaned and it would idle at just over 2k for a few minutes then would die again. I think it mite be something to do with the jetting but the problem is that I don’t have a service manual or anything so am unable to try and find the problem.

Don’t suppose any one knows what’s up with it / how to fix the problem?

[craigT19]

the jetting will always remain constant so i wouldnt think it would be that, try de-coking the exhaust as u said your self it hasnt been run "hot" for a while.

All the best
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Bikes owned :- 2001 nsr125, 1999 zx6r, 2006 yzf-r1, 2009 xmax 250, 2012 yzf-r1, 2015 MT-07
Current bike : - 2016 MT-10
BCF member pops. sadly missed 1945-2003

[mr jamez]

If it has been sat for 3 months the petrol might have gone off, and if there was still petrol in the carb then it might have turned into a gummy mess, perhaps consider stripping it down and giving it a good clean. Have you tried a new spark plug? check that there is a big fat blue spark as well. Also a compression test may be in order just to check the top end is OK.

[Scooby]

Clean the plug up and get the bike running, then go and thrash the tads off it. It has done 400 miles so is more or less run in so don't worry about that too much. Just go and thrash it, 2 strokes need to be thrashed. Once you've given it a good thrash it should run okay, so then drop the oil and it should be fine.
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A big enough hammer fixes anything!

[culpan]

Ok cheers guys will give all them a go and let you know how it goes.

[Frost]

Fresh petrol and 2 stroke oil would be first one the list. Gearbox oil would be worth checking along with a new spark plug.

Provided the bik isnt drinking coolant etc, then the only likely problem would be the powervavle. If it is jammed open, closed, or in backwards it would cause performance issues.