Looking good great job  

Thanks.  And we come to our first real  moment.

I had the carb in bits and cleaned in the untrasonic bath.  We know the main jet is dead because we tried it on the devil bike, it being a 130 same as the devil bikes, and found out someone had "tuned" it sometime in the past.  Looked like it had been drilled out with a masonary bit.
I reckon my 175 was seeing 2.5mpg with that jet fitted.

I had noticed on taking apart that the usual sealing washer was missing from under the float valve seat and on checking before removing, the float height was about 18mm.  Looked it up and should be 26mm. Ha! Probably because the washer was missing.
Found a 7 x 10 x 1mm fibre washer at work and fitted that and discovered why the washer was missing....

The previous "tuner" had removed the float valve seat and on refitting, had overtightened and partially stripped the threads.  I guess the washer had been removed to get a bit more thread into play.  .

The chamber above the seat has a side entry and I can see where omitting the washer may cause this orifice to be partly covered by the end of the valve seat.

Makes you wonder if these "tuning" modifications were the cause of the bike getting laid up all those years ago?  It must have run like crap and the "kid" lost interest in it.

So I had to think outside the box, or to be really honest, bodge the feck out of it.  The threads would catch with the washer on, not enough to get a good tighten but at least double finger tight.  I blathered the float valve threads with thread seal/lock and dogged it down as tight as it would before slipping.  My new sealing washer being relegated to the role of a simple spacer.

Not great.  But short of finding another carb, best I can do.

Trying to find a carb is a bit of a sod.  I believe it to be a Mikuni VM22, but all the VM22s I am coming across are all flange mounted for four strokes.



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This no good to you?

YAMAHA DT100 DT100D 1977 1T9 CARBURETOR CARB | eBay

Thanks GR8.  I had seen that one, but the seller is away for the next fortnight.  I wanted to contact him to gets some pics inside.
​​​​​​It looks well grotty.  

It is the correct carb though.  The 1T9 prefix carb was only ever fitted to the 1977 US and Canada model.  1978 carb prefix is 2F5.

Footrest bar and sidestand assembly completed.  Everything in the pic was fitted by a production operative on the Yamaha production line back in 1976.
I find it quite remarkable.  I wonder if that operative is still with us?  If not, his legacy lives on...

You might find an OE carb, but would need a fair amount of luck to find something usable.

Chinese carbs made for Suzuki AX100 clones, are listed on eBay for around £25, and might work fine. 

A brief adrenaline rush just turned to disappointment.  A bike breaker was advertising a carb from a 1978 DT100.  It showed a pic of the actual bike prior to breaking and it is a DT100D like mine in competition yellow.

The very clean carb came with airbox attached and I am also currently seeking the air filter cage.  The only cage so far found has an asking price of £35.  I will not reward scalpers and gougers no matter how much I need one.

So carb and airbox for £68.  A lot of money but it takes care of two issues.  I looked twice...

What is wrong with the carb?

Does not look like an original Mikuni from that era to me at all. Cheap knockoff?

You might try ordering the air filter new from Yamaha. I believe that one comes with the cage these days. I think Kosmo verified this recently. Let me look for the thread.

On 06 Aug 2023 Kosmo wrote:

"Update on this:

P/N: 1T9-14450-01 is both the air filter and the cage, not oiled. "

 

Its a Chinese Mikuni copy, available from ebay for £25. Might work perfectly though...........