pinholes in both CV diaphragms

Cousin brought her '79 KZ400 to me after ten years in the barn. I found two pinholes in each diaphragm (and one of the holes on the right actually has a star shape).

Slides/diaphrams appear to cost $320 for the pair. These carbs are labelled "1209 RK13", engine is K4E142628 (I think it was swapped, so it's possible they don't match years). Are there any good options? This KZ already has pod filters and gravity petcock, so anything that bolts-up to the engine is an option.

It looks as though beat-up carbs on eBay in Fair/Poor condition cost $100 or so, but it's anybody's guess if they would have good slides.

Single-carb manifold (11th hour) + MK34 carb looks like about $250.

I have seen a KZR member glued the pinholes with an small thin piece of a rubber glove. I would give it a try.

A google search produced an old, old suggestion to use Plastic-Dip to mend a tear in the diaphragm on a BMW650:
www.650central.com/frepairing_a_tear_in_the_carb_dia.htm

I have some "liquid electrical tape" that might work, but the plastic-dip aeresol spray might give a thinner coat. But since that was the only "hit" in the search, it seemed a bit "out there". On the bright side, it doesn't cost much ($10).

Some liquid rubber products won't be fuel resistant.

Gorilla glue has been mentioned on another forum for repairing diaphragms. I don't recall exactly which product was used, but it was a polyurethane adhesives w isocyanate. Elmer's Pro Bond is another one.

Also, JBM Industries might have replacement diaphragm rubbers for your bike & the pricing is reasonable. They have them for the 440 & various other models, but not sure about the 400.
....

Thanks, Martin_CSR. JBM Industries' product looks like what I need. In fact, I may order a membrane for my late-'80s scoot too, "just in case."

I'm dealing with the diaphragm pinhole issue on some older (1977) CV32 Kz400 carbs. Basically JBM industries is the only source I could find, but they don't make diaphragms for the earlier CV32. I think they might have ones for your carbs though.

I tried some diaphragms from a Taiwanese seller, but they didn't quite fit. They were too loose on the slide and also the "dish" was too shallow, which inhibited the slide from dropping all the way. I think they were listed for Honda CB350 carbs.

I'm hoping to email JBM to see if they think I can use diaphragms for a different Keihin that they make.

Maybe I should make a new thread, but the throttle linkage doesn't look right to me:

This was before disassembly.


It looks like the spring (putting tension between left and right throttle positions) rests on the arm from the left carb (shown on right), but passes up THROUGH the yoke from the right carb (shown on left), and only presses against the washer and locknut. That seems pretty useless. I'm guessing that the yoke from right carb needs to go between lock-nut and washer, so that the spring is keeping tension between left and right carbs. Or maybe there should be two washers. Or maybe the spring is just upside down.

I'm used to carbs like these, which have a spring trying to push the two apart, and a tension screw + lock-nut keeping them together:
gs500resurrection.files.wordpress.com/2010/05/dsc00867.jpg

I could be wrong, but I don't really trust anything on these KZ400 carbs anymore (for example, the slides were put in at the wrong rotation, so the notch/ cutouts in the bottom of the slides did not even face the choke plates, and the "keys" in the top edge of the diaphragms were not placed in the indentations, and got pinched/smashed). Somebody even dumber than me has been working on these.

SpecialGreen wrote:
Maybe I should make a new thread, but the throttle linkage doesn't look right to me:

You are right about the throttle linkage.

Thanks, Scirocco. I moved the "yoke" above that washer, and was able to bench-sync. Got the carbs in, and it starts and runs (more or less) with no airbox/filters. It responds well to the idle screw.

Good to hear it solves one of your Problems. I have to fix the same issue on a professional rebuild 4 cyl. carb set.