Where is my diaphragm?

[Spootinay]

picture 9 of thirteen.

im starting to think this carb is off of an fj1100...

My wife has an FJ11, and a while ago she had the carbs out. I happen to have a spare set of XS carbs, so I compared them. I butted the carbs up to each other, at the engine side, and it was a perfect match. The spacing was exactly the same. There are a few minor differences however. The FJ carbs do not have a vacuum port on the #2 carb body for the vacuum advance, so you would have to use a vacuum port off one of the intake boots, and add a restriction, so the advance mechanism isn't bouncing about wildly, and the FJ carbs use two throttle cables, but a clever man can find a way around this problem. Another issue is the size of the fuel line. The FJ uses 5/16" and the XS uses 1/4'' line.

[BA80]

AFAIK, the XS11 is the only bike to use a vacuum advance so your Zuki carbs won't have a port.

True dat!

The bike should run ok without the vac advance.

Dat I ain't so sure about. My bike ran like crap when the advance diaphragm went out.

[BA80]

picture 9 of thirteen.

im starting to think this carb is off of an fj1100...

Not sure what those hoses are but they're not vacuum.

[cywelchjr]

The bike may run ok without the vacuum advance hooked up, but gas mileage will suffer, as the timing curve is designed with the vacuum advance in mind, and to get enough advance without it you need too much advance at low RPM. That said, at least one type of carb it's been figured out how to modify to provide the proper vacuum for the advance, so I expect it can be done for the others since they are the same carbs, they just don't have the ports drilled on the ones not setup for the 11. (at least on the bs34's, but the port exists in the casting, it's the same casting for all of them (at least for a given series such as the series III, but the difference is how the passages are drilled and the jet sizes.

[Spootinay]

so could i drill a hole in the existing casting and insert a tube to attach a vacuum advance line to? I can see where it is supposed to be drilled. from comparing pictures of other carbs.

[mack]

79 carbs

I've got an extra set of 78/79 carbs. PM me if you need them to get riding.

[crazy steve]

You could, but it's a bit trickier than that. The vacuum nipple on the stock carb has a tiny hole into the carb throat, it's not the full 3/16" diameter. And where it is is important too; the stock hole is located so that it's blocked when the throttle plate is closed, and as soon as the plate moves the hole is subjected to 'manifold' vacuum.

Do a forum search; somewhere on here is a post about doing just this, and it details where and how big the hole is...

[Gyrogearloose]

Where's your diaphram?

Oh, man, lighten up. It's not that technical (Heh.), your diaphram is between your stomach and your lungs. Geez! don't put a hole IT!! ....had to do this.

[BA80]

so could i drill a hole in the existing casting and insert a tube to attach a vacuum advance line to? I can see where it is supposed to be drilled. from comparing pictures of other carbs.

It has to be in exactly the right spot and exactly the right size.

IMHO............get the right carbs for the bike.