Carb diaphragm replacement

[.Chris.]

Do these have to be replaced as a set, or can they be replaced individually?

As mentioned in my Z400F project thread, I've found some small holes in two of the four carb diaphragms. New diaphragms are available from NRP but are almost £40 each so replacing all four would be quite expensive. Would it be feasible to replace just the two holed diaphragms?

I'm concerned that the new diaphragms might be more or less supple than the old ones, which might make a difference to how the piston rises/falls and therefore the fuelling. If two of the diaphragms are different to the other two, this might result in two of the cylinders having a different fuelling 'curve' compared to the others.

Or am I talking twaddle? The reason I ask rather than just try it out is if I need to replace all 4 as a set, I'm minded to buy a secondhand set of GPZ550 carbs and use the diaphragms from those instead.
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Chris
1985 Kawasaki Z550F

[A100man]

[Paddy Blake]

I would change the four of them.
If two have holes the others will likely not last long before they have holes too.

BTW I think the springs in the middle carbs are different to the outer two so put the springs back in the carb it came out of.

[stinkwheel]

I would suggest that if the carbs are old enough to have suffered from diaphragm failure, the flexability or otherwise of the diaphragms is going to be negligeable compared to the semi-randomised ovalling on the jets, needle wear, corrosion and throttle valve slack.

What I would also say though, is if two have already gone, how long are you expecting the other two to last?
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[chris-red]

Try repairing them with a inner-tube repair kit.
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[.Chris.]

I'm not sure if at least one of the diaphragms has been repaired before:

https://i31.photobucket.com/albums/c390/chrisd87/Z400F/DSC08332_zpsvsa6pwzj.jpg

https://i31.photobucket.com/albums/c390/chrisd87/Z400F/DSC08333_zpsbtq2ajnh.jpg

To me, this looks like someone has already tried to repair splits in the diaphragm. When held up to the light you can see through the middle of the areas that have been repaired, so I'm presuming they're not air tight. I don't know how feasible it would be to try to repair it again.

The other one isn't as bad:

https://i31.photobucket.com/albums/c390/chrisd87/Z400F/DSC08336_zpsoki3bini.jpg

I may have a go at repairing this one.
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Chris
1985 Kawasaki Z550F

[Paddy Blake]

There is no repair that works that I know of.
Also you are repairing one part of a overall part that will fail.

[Paddy Blake]

It's like if you got an old bike and a chain link broke
then you change that link.?

Would you not think the chain should be replaced.

[temeluchus]

plastidip is good for repairing carb diaphragms.
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[Pete.]

What Stinkwheel says makes sense. Having a stiffer/more flexible diaphragm isn't going to affect you so much, it's the spring that determines the slide movement. The diaphragm is just a seal. It might change the throttle response but I doubt you'd notice it.

Most stick-on repairs are doomed to early failure because of the repetitive action of the slide. Either find some cheaper alternative diaphrams or pony-up for new ones. Replacing two now and the other two later is perfectly fine.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[Vincent]

I agree with above and wouldn't repair one either.
I may have some spare ones .....got a good pic and slide dimensions?
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Space Is Deep

[Shaft]

I haven't tried it, but superglue and bits of condoms are said to be (could be apocryphal) at least a temporary fix.

But as others have said, if two of them are shot, the other two are going.

Personally, unless you can find absolute proof that another set of carbs from another model/capacity are a plug and play swap, I would go with the replacement diaphragms, for all four.

Swapping a bank of carbs seems like an easy fix, but it can also lead to a whole world of sht.
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[Pete.]

One other thing - if you are struggling to re-fit your diaphragms because they have swollen up and are too large to stay in the groove - boil them gently in water, or just leave them in a warm place for a good long while. This is especially true if you have used carb cleaner on them to clean them - it makes them swell right up. You have to drive the solvent out of the rubber to make them shrink again.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[.Chris.]

Thanks for the replies everyone.

I think I'll replace the two dodgy diaphragms and leave the other two for now, but bank on replacing them sooner rather than later. There looks to be enough clearance to get at the carb top retaining screws when the carbs are fitted to the bike, so there shouldn't be too much dismantling necessary to replace the other diaphragms at a later date.

Vincent - that's very kind of you, I'll send a PM.

Shaft, you're no doubt right about the pitfalls of trying to swap carbs. I've got the Haynes manual for the Kawasaki 400/500/550 4-cylinder family, and it seems that there were a variety of carbs fitted to different ages/capacities of machines. The carbs on my bike are the TK26V, which seem to have been fitted to quite a few bikes in the range in the mid-80s, albeit with different needle settings and jetting. My thoughts regarding buying a secondhand set of carbs would have been to only use the diaphragms, and nothing else.

The problem I face is that the Z400F (or more accurately ZR400B1, in the case of my bike) is an incredibly rare model in this country so it's very unlikely that I'd be able to find a secondhand set of this particular model. Sod's law, of course, but there was a set on ebay a few months ago but they went for quite a bit, and I didn't know I had carb trouble at the time so let them go.
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Chris
1985 Kawasaki Z550F