K&L diaphragm issue

[Bergman16]

From searching it looks like it’s common to get a diaphragm in the K&L rebuild kits for Specials that just doesn’t work—the thing just won’t seal, maybe a tiny tiny bit short on the rubber material...

I did the resurfacing and prep of the chamber and mating surfaces with my Dremel and 1200 cloth so it wasn’t that.

Also I looked at Chacal but the link didn’t seem to be there for those kits, unless I missed it.

In the end I was able to clean and dress the old one and will see if it works but is this just luck of the draw with K&L?

[motoman]

From searching it looks like it’s common to get a diaphragm in the K&L rebuild kits for Specials that just doesn’t work—the thing just won’t seal, maybe a tiny tiny bit short on the rubber material...

I did the resurfacing and prep of the chamber and mating surfaces with my Dremel and 1200 cloth so it wasn’t that.

Also I looked at Chacal but the link didn’t seem to be there for those kits, unless I missed it.

In the end I was able to clean and dress the old one and will see if it works but is this just luck of the draw with K&L?

Yup......pretty much any component related to K&L. Definitely don't wanna use any K&L related jets as their numbering crosses over to Genuine Mikuni jets, but their hole sizes are not even close to Genuine Mikuni jets, and K&L flow rating is done differently. This goes for both pilot and main jets.

[bikerphil]

What is it you are rebuilding, the octy?

[Rasputin]

I have had good luck with the K+L kits on the Specials Octy. No luck on the Standards petcocks. If you have one try it out as it does not take long to look and see if fuel is dripping from it.

[Bergman16]

Fix for K&L octy diaphragm from Len at xj4ever.com

Yeah, the octy. However, I got a very nice email from Len at XJ4ever.com about how to kludge the KL diaphragm, I'll post it below. They sell them and are aware of the issues. I ordered a replacement spring from him since mine seemed a bit weak.

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NOTE: there is an issue with some XJ700, XJ750-X, and XJ900 petcocks, and the XS/XJ1100 fuel distribution valve bodies where the o-ring seat for the diaphragm plunger was not drilled "straight" (perpendicular) to the mounting face for the diaphragm.......this is possibly why the original petcocks used a hollow o-ring, that would deform more easily to compensate for this (slight) mis-alignment situation......although this issue normally manifests itself as a drip-drip-drip type of leak, rather than a "pouring out" type of leak.

On the affected petcocks, we’ve found that it is necessary to slightly “lengthen” the plunger shaft distance, and the best way to do this is to use an appropriate sized deep-well socket, and place the plunger shaft/tip down into the well of the socket……so that the round metal disc will be sitting on the top of the socket opening, with the plunger shaft down inside the socket well.

Now, take a small hammer (or hammer-like object) and GENTLY tap on the tip of the shaft sitting above the disc, thus “dimpling” the disc in the center JUST SLIGHTLY and thus moving the plunger tip (with the o-ring) “closer” to the seat in the petcock body. This dimpling should BARELY make a concave surface out of the round. previously-flat disc.

As mentioned, some of these petcocks actually had their o-ring seat drilled slightly off-center (or cockeyed) in relation to the plunger shaft…….original plungers used a HOLLOW o-ring that could easily deform to make up for this slightly off-kilter orientation of the shaft vs. the seat. The replacement plungers use a standard, solid o-ring and this cannot deform as much as the original hollow o-rings do. By dimpling the support disc, and in effect “extending” the length of the plunger shaft, the solid o-ring can take up any tiny amount of slack caused by this non-alignment issue.

What is it you are rebuilding, the octy?

[bikerphil]

That info ^ is good to know, thanks for posting it.

[Bergman16]

Just to follow up. I tried that disk fix and it worked like a charm—at least off the bike and on the bench it seems to close up tight about a second or so after I release the vacuum (me sucking on the vacuum line).

Even though I kept the bike on the side stand and the leaked gas came thru the airbox, I’m going to change out the fairly fresh oil before I go anywhere. Can’t smell gas in there but I don’t trust my nose.

Hoping to not tear down the carbs to chase a sticky float until this winter.

[madmax-im]

Len at XJ4ever... is awesome...

[Radioguylogs]

Hmmmm, might work for other applictions

Since the beginning of time, most of us on the XS750 forum gave up on fixing the vaccuum actuated petcocks on those bikes. The K&L kit doesn't fix them most of the time. I suspect this fix could improve the success rate!

[Bergman16]

I wonder if swapping out the little o-ring would also help—assuming the old one is in good shape? If it is indeed hollow (I didn’t investigate this but I will) that seems superior for sealing as Len said.

Regardless I don’t see any reason why this wouldn’t work with vacuum petcocks. I have one and a KL rebuild kit (I’m restoring a Venturer tank) so I will test and report.