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From: tylernt on 18 Mar 2007 11:37
> Suggest you do some searching on the Mikuni USA website. There's
> a .pdf manual there for their normal carbs, may also be one for CVs.

I did find http://www.mikuni.com/fs-manuals.html, but I don't know
enough about carbs to tell which kinds are CV or what. I also found
http://i19.tinypic.com/3324bci.gif which was helpful in identifying
some of the other passages, but the mystery hole doesn't seem to be
called out in it. At first I thought it might be part of the starter
jet system, but when I blow compressed air in the little tube (not the
main jet, the other one with a hole in the side) that sticks down in
the flow bowl, air comes out the choke opening so I don't think that's
it.

Another thing I'm interested in is the pilot screw setting... but I'd
be happy just to have a bike that idles.

From: tylernt on 18 Mar 2007 11:57
> > flow something, why do I see brass a short ways down the hole?
>
> Because it's the non-removable PILOT AIR JET. When you have a CV

Ah, thank you!! Your explanation makes sense. I guess I'll have to do
more work to get the gum out. Yeesh, sure makes me understand the
value of adding cleaner and stabilizer to the fuel tank -- what a pain.

From: Potage St. Germaine on 18 Mar 2007 12:04
On Mar 18, 7:37?am, tyle...(a)gmail.com wrote:

> I did findhttp://www.mikuni.com/fs-manuals.html, but I don't know
> enough about carbs to tell which kinds are CV or what.

CV stands for "constant vacuum" or "constant velocity" at the venturi
under the vacuum operated slide.

CV carbs will have a rubber diaphragm or a vacuum operated piston that
lifts the slide to which the jet needle is attached.

In older, slide valve carbs, the slide was the throttle and the rider
had direct control over the slide's position. If he turned the
throttle grip too far, the jet needle could be pulled too far out of
the needle jet and, since the slide valve carburetor doesn't "know any
better", a huge gulp of fuel would be sucked into the cylinder, only
to be ejected out the exhaust pipe, unburned.

CV carburetors give control of the slides to the available engine
vacuum. Vacuum doesn't actually pull the slide up, it's *air pressure*
under the diaphragm or piston that actually lifts the slide. Engine
vacuum pumps air from above from above the piston or diaphragm, and
air from below lifts the slide.

> I also foundhttp://i19.tinypic.com/3324bci.gifwhich was helpful in identifying
> some of the other passages, but the mystery hole doesn't seem to be
> called out in it.

Nice diagram of a SUZUKI carburetor, it shows the cross-drilled holes
in the pilot jet and the rubber plug under the idle jet that a Mikuni
BS34SS would have.

Did you find rubber plugs concealing the idle jets?

Maybe what you have are actually HITACHI carburetors. Some Yamaha
owners have expressed displeasure with the lack of tuneability of
Hitachi carbs, some of which didn't have interchangeable screw-in
jets.

> At first I thought it might be part of the starter
> jet system, but when I blow compressed air in the little tube (not the
> main jet, the other one with a hole in the side) that sticks down in
> the flow bowl, air comes out the choke opening so I don't think that's
> it.

That little brass tube IS the "straw" with the starter jet in it.
>
> Another thing I'm interested in is the pilot screw setting... but I'd
> be happy just to have a bike that idles.

As previously stated, the number of turns on the pilot screw is VERY
dependant upon the area of the idle jet orifice, and anybody who tries
to tell you an exact beginning setting is thinking of the old slide
valve carbs where 1.0 to 1.25 turns out was a typical setting.

But slide valve carbs had AIR screws, not gas screws.


From: tylernt on 18 Mar 2007 12:28
> > I also foundhttp://i19.tinypic.com/3324bci.gif which was helpful in identifying
> > some of the other passages, but the mystery hole doesn't seem to be
> > called out in it.
>
> Nice diagram of a SUZUKI carburetor, it shows the cross-drilled holes
> in the pilot jet and the rubber plug under the idle jet that a Mikuni
> BS34SS would have.
>
> Did you find rubber plugs concealing the idle jets?

Yes, I did.

> Maybe what you have are actually HITACHI carburetors.

They are stamped 'MIC" on the side... dunno if that means anything.

I'm pretty sure I got all the other jets clean with B12 and compressed
air... it's just these last two "pilot air jet" holes up on top.
Unfortunately there are some rubber seals on the "choke" (cold
enrichment device) rod so I can't dump the whole thing in a bucket of
cleaner overnight, so I'm relegated to spraying a puddle in there and
going at it with toothpick, I guess. But, I should be able to get
cleaner in there better once I remove the pilot/idle mixture screws
(after counting how many turns they're up from the bottom).

Thanks a million for the info! This is all information that should
have been in the book, if you ask me... so I'm grateful for the help.

From: John Johnson on 18 Mar 2007 13:02
In article <1174232231.356326.86240(a)p15g2000hsd.googlegroups.com>,
tylernt(a)gmail.com wrote:

> > Suggest you do some searching on the Mikuni USA website. There's
> > a .pdf manual there for their normal carbs, may also be one for CVs.
>
> I did find http://www.mikuni.com/fs-manuals.html, but I don't know
> enough about carbs to tell which kinds are CV or what. I also found
> http://i19.tinypic.com/3324bci.gif which was helpful in identifying
> some of the other passages, but the mystery hole doesn't seem to be
> called out in it. At first I thought it might be part of the starter
> jet system, but when I blow compressed air in the little tube (not the
> main jet, the other one with a hole in the side) that sticks down in
> the flow bowl, air comes out the choke opening so I don't think that's
> it.
>
> Another thing I'm interested in is the pilot screw setting... but I'd
> be happy just to have a bike that idles.

http://www.factorypro.com/tech/carbtun.html

How to set your carburetors, from people who know what they're doing. HTH

--
Later,
John

johajohn(a)indianahoosiers.edu

'indiana' is a 'nolnn' and 'hoosier' is a 'solkk'. Indiana doesn't solkk.
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