Ok so my DT400B is probably suffering from lack of use. My bikes often sit for weeks without being started and used for their intended purposes…..

But I recently posted that my carb slide is badly scored or scratched vertically. The reason I even noticed is because the bike is not running well and it used to be my pride and joy. Would always start on second kick and ran well with the only issue being the common issue with this particular model and that is sputtering somewhat when it plains off at cruising speed. Roll the throttle on and it’s fine.

Well it’s got new issues. The first video is sound only. You will hear me start the bike and pull away from the garage. Then you will hear three gears of mild throttle application with it sputtering like mad. You will then hear me turn around and run thru three gears at full throttle. It accelerates fine and sounds good to me at full throttle. My issue is at idle thru mid range. You will hear it idle and stall at the end of the video.

The second video was taken when I was going to adjust the needle clip. With the slide removed, I noticed fuel dripping from the intake of the carb at the air cleaner. I don’t think that’s normal even if the slide is removed.

So maybe my scored slide is telling me that this carb needs new parts. The needle looks worn to me. Maybe I should buy new slide, needle, float valve and seat, the works. Or maybe you guys can tell me what to try next. youtube.com/shorts/AoRdXlsC88I?si=Dxe6SkiSFx16TLjj

FLOATS/DRIPPING: are they floating? ie, maybe constant fuel flow and thus over-flow? Hows the seat look?

SLIDE DAMAGE: Not sure the cause there, air filter leak, open reeds, ... I would believe that if you are sucking air through a leak, then maybe your 3.0 cutaway is now acting like a "4.0" and would run leaner at idle, yet does not appear to.

NEEDLE: your needle looks a bit worn down and I would suspect some excess fueling. That may be affecting the throttle transition you mentioned.

WOT: I would think the fueling would be less affected at wot vs part, but I also would have expected a lean condition and yours did not.

Based on listening to it, it does not sound lean, so is slide really causing a problem??? I would replace anyway.

My vote is for carb rebuild!

Gotta love the video though. Not enough 2 stroke noise on this site.

This might help with parts... yamaha-enduros.com/index.php/forums/74-7...oat-needle-set#92571
 

Thanks Mark. I had found that same post and have already reached out to DEET. I am hoping that he can help with the remaining bits.

The new slide should be here today. The eBay seller who had it listed for $50 must have seen that I viewed the listing because he sent me a message and offered it to me for $38 so I bought it.

Schu,
If you give up on that carb I have some DT400 B and C (marked 500 61 and 500 63) carbs that I would part with if you are interested. I only need one for the DT400C in my avatar. I also have some new Mikuni needle jets and jet needles for these carbs. I haven't tested or cleaned any (except cleaned the painted one at the top of the picture).

PM me if interested.

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They changed the imjur interface and I can't embed pictures correctly.  Sorry.

imgur.com/a/oSNjvVE

Thanks JayB.
I haven’t given up on it yet, but that’s a nice box of carbs you got there. I will reach out to you if needed. Much appreciated.

So if that doesn't sound lean when accelerating is is it rich or good?

She's plenty rich at idle & all the way up to pretty much main jet. I'd be sorting the float valve & float level first because of the flow out of the air cleaner then try again.
But i'm wondering about wear in the needle jet [called emulsion tube].
They wear oval shaped at the top where the needle runs & the needle wears too.
Or someone has a bad combination of needle & jet tube.
Also check the pilot jet is fully home in the carb body & mixture screw is about 1.5 turns out.
Fuel overflow problem first though.

Hey Morley, that is somebody else (Dogboy) asking the question in regards to my original post.

My status on this issue is that I am simply waiting for the carb parts that I ordered from DEET. I will update this post and hopefully close it out once the parts are in my hands and I get them installed.

Ok SCHU haha, it's a bugger being old & confused. All good Cheers.