Diaphragm Slide Orieintation

[79special]

Hi All...

New to the Forum, Great Site... Lot's of good info.!

During a recent winter project to rebuild the carbs on my 79 Special, I noticed an interesting scenerio with the slides.

The small angled vent hole in the bottom of each slide is positioned at a differnet angle in relation to the airflow... Each carb is slightly different.

After doing a bit of close inspection and light cleaning of the slides and diaphragms, I noticed that each one of the slides can turn inside the rubber diaphragm. Since the orintation of the slide is not "locked" into, the slide would be able to turn inside the carburator bore.

In pondering that fact a bit... it seams that there could be slight variations in pressure/vacuum caused by airflow passing over the vent.... which could cause each carb to run rich or lean...

Here is my question to all the gurus...

What is the correct orientation of the angled vent hole in relation to airflow through the carb?


Thanks...

79Special

[randy]

Man, that's a great question!

IMHO, it wouldn't matter, because the vacuum in the general area of the needle wouldn't differ that greatly no matter where the hole was oriented.
Why don't you just orient them all the same. Once you get them in place, I doubt they will spin out of place, there's no spinning force exerted on them.

[skids]

Well, I have a set of carbs from an 80SG (I think) that had three of the holes directly down wind, and those lock rings were so tight that it must have been factory. The 4th carb was movable and the hole was to the side.

[AlanB]

Hi Guys,

I have spent a couple of days stripping a few seta of carbs in order to build one totally "good" set. All of the slides were fixed tight in the diaphragms.

AlanB

[TADracer]

Not sure which direction the holes are on my 79 special but I do know that the slides definitely do not turn in the diaphragms. And each diaphragm has a tab that orients it properly in the carb body.

[red bandit]

The slides shouldn't turn in the diaphragm and the hole goes toward the engine. This is how everyone is that I've seen that hasn't been turnable.

[79special]

Could it be that there are 100's maybe 1000's of prefectly good XS1100's out there with this fairly simple, yet frustrating condition caused by approximately 30 years of use, vibration, cleaning and tinkering that could be fixed (or at least made more consistant) with a relatively simple twist, careful alignment and bead of epoxy?

Hmmm... Straight downwind and non-rotateable is sounding right...

I love it when a plan comes together.


Thanks everyone!

[somesuch]

There is seller on Ebay selling replacement diaphragms. I asked him for the procedure for replacement, and he sent me his instructions. Seems that it would work to fix the rotating diaphragm syndrome......

Here is what he said:

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SLIDE DIAPHRAGM REPLACEMENT


The instructions below should be read through a couple of times before attempting to replace the diaphragm/s. If you have access to a press as well as a lathe you can make up a tool to take the place of the engineers hammer and simplify the operation.


1) Before removing the diaphragm take note of where the locator tab is on the outside of the old diaphragm. Use a marker pen to mark the slide adjacent to the locator tab. The easiest way is to push the diaphragm against the side of the slide.

2) Place the slide in the lathe chuck (use a strip of cardboard wrapt around the slide to protect the slide from the chuck jaws). Tighten the chuck. (diagram 1)

3) With good sharp lathe tool (B) start removing the pressed shoulder (A) in small cuts from the top of the slide, cutting it parallel to the slide body so the overall length of the slide including the flare is not reduced. Keep removing material until you can just ease the upper plastic retainer (C) off the top of the slide (you can carefully prise it off with a sharp flat bladed screw driver or similar)

4) Remove the slide from the lathe chuck, remove the old diaphragm, file or machine a very slight bevel on the outer edge of the machined area to assist refitting the plastic retainer. Fit the new diaphragm and align the locator tab with the slide, refit the plastic retainer.

5) Place the slide sitting upright on a solid surface (if the surface is metal place thin cardboard under it to protect the slide). Place the ball end of an engineers hammer in the upper end of the slide to act as a flaring tool, strike the normal end of the hammer with a soft faced hammer e.g. copper. If you only have another steel hammer, use duct tape wrapt around the striking face of the hammer and use eye protection as hammers heads can chip. Do not fully press home the flare until you check the locator tab is in the correct place and the diaphragm is seated correctly in its locating groove, To locate it in the groove gently pull the diaphragm away from the side (pull radially) working right around the slide. If it is out of alignment rotate the diaphragm to align. Finish the flare, by placing the hammer flat face on the flare and striking the ball end of the hammer. If the hammer face is too large use an appropriate sized socket or similar. When finished you should not be able to rotate the diaphragm on the slide. (diagram 2) © A.L. Saunders 2007

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There are a couple of diagrams that he included, but I am not sure how to insert them here.


--Nick

[79special]

Thanks for the diaphragm replacement steps there somesuch, I've noticed those as well... Do those also come with New Plastic retainer rings?

I was actually thinking that sinse, all of the rubber on mine stills looks like there in pretty good shape so I cound just put a carefully placed bead of epoxy around the top of the slide between the plastic ring and the crimped alluminum cylinder after making sure vents are lined up.

That should be just enough to keep the slides from moving around.

[somesuch]

No, they do not. just the diaphragms.
--Nick