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Yamaha DT 125 LC MK1


Tony04
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Hi, I'm new to this forum tonight, after struggling for a few days I've decided to join and ask for help.

I've got a DT 125 LC MK1 

When I first brought this bike a month ago as a project, it would start fine but wouldn't rev up past 1/2-3/4 throttle and seemed lacking in power, I stripped the carb down gave it a good clean out and see that the main jet was a 140 and the pilot was a 25.

I ordered new jets for it so it's now got a 20 as a pilot and a 100 as main, I chose 100 over a 80 as it has a sports exhaust on it, updated reed valves and a aftermarket filter. 

I've been and fitted the carb on the bike tonight. It was a struggle to get it to start and now it will only run on choke, as soon as you push the choke button in it gradually dies and you cannot rev atall to stop it. It still doesn't rev up properly and it's very smokey now, leaves a cloud behind when you ride it. 

Can someone please shed some light on this before I throw it in the scrap ? 

Thanks Tony 

 

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  • Moderator

100 main is far too small, that's why its screaming for choke. Without the 25 idle your making things even worse. Ported properly with a good pipe and filter  these could have a 200 main depending on the other jets.

Someone may well have fitted a different needle and emulsion tube, matched to a 140 main. If you have these with a 100 main it will never run. If you have cut the fuel right back your smoke will be all the extra oil the engine is getting from the pump. Please don't mess with it. Pumps only kill bikes when people mess with them blaming them for problems caused by running out of oil or thrashing from cold.

Put the originals back for now cleaned and at the very least do a plug chop.

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  • Moderator

Have you tried the 140 now the carb is clean. 

With the pipe etc you are into guesswork. It had a 140 so that's where to start. 

You have checked the earth's, plug cap lead etc and the plug. Always job No1 with running issues on a 2 stroke. 

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