Airbox Z1

So my 76 Z900 came without an airbox fitted and 28 mm carbs. Taking the advise to fit a Z1 air box to heart I ordered one, and received it today. In three parts.
So I've got a rubber part , a plastic box with a lid and a steel U shaped part with some holes in it. So the plastic bit and the rubber part is easy.

But where does the metal part go?

Any help and or pictures would be greatly appreciated

Thanks in advance!

Without any pic of the U shaped part i would say it belongs into bottom of the air box between carb air intake tube# 2 and 3.

Sirocco is right. Here is a photo looking from back to front. You can see the hole in the plate sits over top of the hole in the bottom of the airbox. The rest of the metal extends upwards.

I'm not sure what the metal is intended to do. Maybe stiffen up the intake? It seems to block intake to #2 & 3 carbs. Thinking back to the '70's I don't remember ever seeing this on my bike, but I've forgotten a heck of a lot of things since then so maybe it was there and I just don't remember. I don't have it on either of my Z1's but I have a spare with the metal piece inside. I also put a Z1 airbox on my 1980 KZ1000 and didn't use the metal piece.

We've never seen an unmolested OEM Z1 airbox that didn't have the metal stiffener inside. We do see lots of loose brackets sans airboxes at swap meets for some reason. It can be a PITA to finagle one back inside the airbox plenum once removed. It helps if the airbox is heated to make it more pliable. Immersing the airbox in hot water while inserting the bracket works well. The yellow arrows in the second pic below shows how the bracket partially intrudes into the #2 and #3 carb boots in the plenum. We've wondered if that was intentional, in an a crude attempt at balancing intake pulses across all four carbs from the plenum, not unlike the much more sophisticated unequal-length intakes from the plenum on modern sportbikes. Or maybe it was just cheaper to not trim the bracket for clearance, which is more likely.




Good Ridin'
slmjim & Z1BEBE

Thanks guys, thats cleared it up. The rubber part is still so plyable i can slip in de inner parts without any trouble.
It's almost too soft.

So how do I secure it once I've mounted it to the carbs? Just tiewrap it into place ?

It should stay in place by itself.

Did you have the plastic air filter insert put into the rubber part of the air box???



Air inlet cover on top of the air box

hvdm wrote: ... So how do I secure it once I've mounted it to the carbs? Just tiewrap it into place ?

On Z1's there's a forked bracket bolted to the bottom of the battery box that supports the weight of the airbox assy. at the rear. The forked end of the bracket straddles the filter cavity drain, which is the short, hard nipple directly below the air filter, not the nipple for the rubber elbow at the bottom of the plenum.
Left unsupported, the weight of the rack of carbs, airbox & filter assys. bouncing when the bike is in motion stresses the carb boots, mostly downward, hastening splits developing across the top of the carb boots as everything rearward tends to sag.
We're unfamiliar with the chassis/battery box configuration of KZ900's in the airbox area. If existing bracketry does not lend itself to supporting the weight at the rear of a Z1 airbox when installed in a KZ900 frame, we'd suggest tie wraps or other means of support.

Good Ridin'
slmjim & Z1BEBE

Thanks guys, that's clear.
Is it worth it to use a bit of hot glue to secure the metal insert in place? to secure i t? It seems to met it can slide out of place quite easily and block te drain holes and intake both? Or maybe use a hollow bolt to secure it through the rubber nipple?

Scirocco wrote: Did you have the plastic air filter insert put into the rubber part of the air box???

Air inlet cover on top of the air box

Yes it was complete . Luckily I double checked because the top was stuffed in with a piece of paper which i'd trow away otherwise.

hvdm wrote: ... Is it worth it to use a bit of hot glue to secure the metal insert in place?...

Unless the metal brace is seriously misshapen, it should be pretty firmly held in place by the surrounding plenum rubber.
Note that the hard plastic filter housing is separate from the rubber plenum, and the metal bracket lives in the plenum itself.
The hard plastic filter housing extends from the screened opening all the way down to include the filter cavity drain nipple, so that the filter is surrounded by hard plastic, with a large opening into the plenum. The filter housing is simply pressed into place, surrounded by rubber with only the top 2" or so of the neck exposed.. Examine your airbox closely & you should see what we're describing. The plastic filter housing will just pull out of the surrounding plenum rubber. The metal bracket cannot be easily inserted into the plenum with the filter housing installed. Immersing the entire airbox assy. into hot water long enough to heat & soften the rubber will ease removing & installing the filter housing significantly.

Good Ridin'
slmjim & Z1BEBE

Thank you . With you're explanation it makes sense.