Off topic...  had to look up that song...  was apparently played here but can't remember ever hearing it before though I'm sure I have.  Catchy tune but creepy sad topic.  Amazing how it was such a big hit in other areas of the world and not here.  That seems unusual? 

Over here we have a place called "Harbor Freight" that sells discount tools.  Their ultrasonic machines are pretty small.  I bought the smallest one first which was barely big enough for the tiny VM14 carb... 

I eventually bought their bigger one with heat and while it "buzzed" it was not very powerful.  I took it back and exchanged it and that one is much better.  The small one still seems the most powerful.  I have a friend with a 3 or 4 quart one that is very powerful.  Another friend bought what looks to be the same 3 or 4 quart model but definitely isn't as powerful.  Quality seems to be all over the place in my limited experience.  I'd try to buy from someplace you can return/exchange easily which is why I haven't bought a bigger one yet. 

Thanks all.
Not too sure I’ve got a starter jet in my float bowl (DT400 Twin shock)? I’ll have a closer inspection when I strip it down again.
I never remember to switch off the fuel after stopping the engine (I never did back in the day (DT50m) and never had any problems) and the carb keeps overflowing. I’ve set the float height, got a new float bowl gasket, cleaned the carb a couple of times with carb cleaner etc. (the carb is black, so there sometimes small flecks of black paint floating around - which is a bit of a pain)
New Mikuni jets etc are very expensive, so I thought I would give the ultrasonic cleaner a go…


 

"New Mikuni jets etc are very expensive"

Try going to Motocarb, a Mikuni supplier.

Sounds like you need a new needle and seat...  not a cleaning? 

Try a Mikuni parts place.  Yamaha gets crazy money for some of the needle and seats...  like $80.  Same part can be found at Mikuni place for around $20.

Try this post...  has specific info on the Mikuni needle/seat part needed for the 75-76 DT400.  yamaha-enduros.com/index.php/forums/1977...00-carburetor#107457

"The 1976 dt400 takes a VM28/163-2.5 partzilla shows the 34mm using VM28/163-3 The number is stamped in the female part 2.5 or 3.0 "

"Not too sure I’ve got a starter jet in my float bowl (DT400 Twin shock)? I’ll have a closer inspection when I strip it down again."

Phil I'm not familiar with your exact carb but looking at the removed float bowl from above there should be four holes for mounting the bowl to the carb body and a fifth hole at the bottom of which is the "fixed" starter jet, but I could be wrong

Hi all, thanks for all the information.
I’ll give motocarb a call and try and get a new needle and seat - and give the carb another clean (starter jet included!) ….

 
MarkT has posted a real clear picture of the starter jet located in the float bowl. Definitely hard to see and I usually use a strand of copper wire to clean it.
 

Hi MarkT, I'm a bit confused about what document details the correct model number for my float valve. Sorry if you have already explained and I have missed it.
I hope you can help me....
My DT400B is a 1975 model. The carb (according to the service manual) is a VM32SS/1. Previous posts have talked about a VM28?... and a 34mm?
I will check the size (2.5 or 3 etc) when I dismantle the carb (this assumes the correct one is in there at the moment).
Where can I find a reference to the correct part that I need? Is VM28/163.... correct or do I need a VM32/163.... part?
And where does the '163' come from?
Thanks again for your help....

No need to be sorry...  I posted a quote from Yamahoper's post and it might have been out of context...

VM28/163 is the basic part number.  On his DT400 he had a 2.5mm valve but he said Partzilla said it was a 3.0mm. 

(The 2.5 or 3.0 will be stamped in the valve seat part)

If you need a 2.5 you would order a VM28/163-2.5 (or maybe -25, I've seen it both ways)

That's for the exact replacement original style metal-tipped valve.  The Mikuni specialist might be able to supply an equivalent part with a viton-tipped valve if you ask them.  Viton seals better. 

When you start looking at parts and carb numbers it gets extremely confusing...  Mikuni had several "body sizes" and then sometimes a company like Yamaha modified those specifications even more ending up with a bespoke arrangement...  So even though your carb might be called a "VM32", it takes the VM28 type float needle and seat. 

(I'm not an expert but I call the basic sizes these bikes used I call small body, medium body, and large body...  the basic numbers are VM24, VM28, and VM32....  in your case, you have a "medium body" based on the VM28 even though it's a 32 bore.  Some of the small MX bikes had 30 bore carbs based on the "small body" VM24.  And of course there are even smaller carb bodies and bigger ones than those three basic sizes.  But those are the most common "body sizes" for 125-400 Yamaha enduro and MX bikes from the 70's.)

 

Many thanks MarkT for taking the time to explain all that to me. After nearly one year, my bike is nearly ready for its maiden voyage. Just a few annoying niggles to sort out and I’m there…
Thanks again.