Cv carb diaphragm cap question

[thebrandonbeezy]

This is the cap off of one of my bst38ss carbs, it has that vacuum nipple.. what is it for and where does it go. On my fzr one of the caps was missing for who knows why.. well these caps bolt on but the fzr has the vacuum routed into the chamber of the cap instead of to a nipple. Just wondering what the difference is and the purpose of this is

[Steve]

Might have to ask that on an FZR forum, because none of the GSes have a cap like that.

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[thebrandonbeezy]

Im still waiting to have access to the fzronline forum but i think its dead haha. Anyways the cap pictured is off a suzuki i believe early 90s not sure what though. Im missing one fzr cap and the suzuki cap bolts on but i needed to know how those vacuums were ran.

[thebrandonbeezy]

Was gonna just run all four zuk caps since i have them

[Steve]

Anyways the cap pictured is off a suzuki i believe early 90s not sure what though.

You might have to spend some time browsing parts fiche to see if you can find one like that, then look up a service manual for that bike.

That is the kind of challenge I enjoy, but my employer has other plans for my next 6 hours or so.

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[Joe Garfield]

Nessism might now...

[thebrandonbeezy]

Ive done a little Googleing and it appears theyre off of a 93 94 ish gixxer 750 and the vacuum nipple gets capped off on them. Looks like its tapped right into the throat of the carb behind the throttle butterfly on the gixxer. Now since the fzr is routed back into the chamber of the cap would that be for better throttle responce? I may try the gixxer caps with the tubes capped off on the fzr since i cant find any fzr caps on ebay unless i but an entire rack of carbs (not anywhere close to being in my budget)

[thebrandonbeezy]

I dont mean to put yamaha stuff on our gs forum, but theres a lot of knowledge here soo yeah

[Steve]

Can you tell if the port simply vents above the diaphragm? If it does, and you connect to engine vacuum (between the throttle plates and the engine), that would simply hold the slides up all the time. Might be good on a race bike, but destroys the basic operating principle of a CV-type carb. The slide is supposed to move in relation to the airflow, to allow higher velocity at lower speeds to maintain crisp throttle response. If you hold the slides open and crack the throttle open, the engine will fall flat on its face.

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[thebrandonbeezy]

Ill take pictures after work, it goes to a port in the carb body

[thebrandonbeezy]

Ok so here's the bst38ss set up, will be going to my shop to open up the fzr carbs to compair

[thebrandonbeezy]

the brass nub protruding through the aluminum body is where the cap nipple is located. But rerouted to the cap chamber on fzr
you can see the tube runs down to the throat of the carb and meets with another tube

[thebrandonbeezy]

it joins in with this and this.
And then joined to the bowl aswell. now i ran the one cap on the fzr open just to hear the bike run, and it ran good but i couldn't ride it cause it was stuck between gears. Now im thinking of just running all four zuki caps and capping off the nipples like it would be on the zuk? Idk

[thebrandonbeezy]

A few more..

[thebrandonbeezy]

fzr cap
top of fzr carb