Hi All,

Got a DT400mx import last month, its a little dream of a bike in good baseline nick. Got a bit of work to do yet though before I can justify getting the paint & decal work sorted.

It starts perfect and idles fine, the trouble is once it goes onto main jet it bogs out atrociously. Done a bit of minor tinkering ie. new plug & air filter, but to no avail.

Took it up the road the other day (in third) and turned the fuel tap off for a brief moment and there was a short burst of power which suggests an excessive fuel flow.

Got a carb referb kit to fit to see if that will sort it (with float height setting check).  Thing is the carb has a lot of new looking screws & fittings on it as though someone's been in there before.

So prior to performing "surgery", my questions are;

1) is it possible that there is too much oil going in on the auto lube?

2) could this be a crank seal issue & what are the classic symptoms of seal failure?

3) been hearing a lot about crap original CDI etc. any truth in this?

Got a lot of faith in old DT's,  the 175's & 250's both have a great reputation and I had a go on both in me younger (wayward) days in the 80's with fond memories.

This is my first venture with owning a stroker and was anticipating simplicity on the engine front so if anyone has had similar DT400MX experience please feel free to share,

Will update once I've fitted the carb kit & checked float height.

regards Max

Hi max" ,the CDI"s  [OEM]  are ok, am running the original ,  i had the Rex speedshop settup. and it failed ,  [ its him that says the old cdi"s are crap] ,  i told him it failed ,and his only reply-   "weve   done  an upgraded version"  ,so i said trade the old one against one,=   No reply,

So,   back to the carb,,change the jet setter,[immulsion tube]  and needle,   as if they are worn  ,more fuel get sucked thru ,.   what colour was the plug ?  ,,,

Read this.   see what i mean ,

https://yamaha-enduros.com/index.php/forum/performance-improvements/7305-rex-s-electronic-ignitions