KZ305 Air Box Boot Alternative (3D Print/Rubber Coupling)

Hello,

Thought I'd share an idea I am working on to fix my KZ305 air leak issues through the air box. Would appreciate any feedback or input to improve the design.

The original boots that came with the bike are very stiff and have shrunk over time causing them to be too short to properly grab the carb opening when clamped. After searching for quite a bit and not being able to find good replacements I tried using a PVC flex coupling since the dimension were close enough to make it work. The coupling has two recessed sections (blue arrow) for clamps which match the opening on the box snugly. After trimming the excess I was able to clamp it down to the carb to make it work for a while. Over the course of a few months the boot started to bulge (red arrow) due to the compression between the box and the carb. It also got a bit stiff and started to deform on both the clamped end and the free end on the box. I suspected I had air leaks since I couldn't get the bike to run properly and the idle was all over the place.


After thinking for a bit I though I could try making an adapter that I could secure to the air box opening, with a section coming out where I could mount the free end of the hose and clamp it. For the first test I'll use the PVC hose again but the plan would be to use 2in/55mm fuel filler hose since the PVC doesn't play well with fuel.

The adapter itself printed in a bit less than 6 hours and it consists of two pieces.


Piece A goes inside the box and has a taper to simulate the shape of the original rubber boot curved intake. This is easier to print but I might try a round shape later. The flange on the inside sits flush against the flat face of the box. The part that comes out of the box has two channels for Piece B to slide into. The channels are 180 degrees apart to provide good support and are angled with a slight taper to end in a snug fit.



Piece B also sits flush against the (outer) flat surface of the box. It acts like a nut as it clamps to the air box face while it is turned. Time will tell if vibrations will knocked it loose, but right now it is a pretty tight/friction fit (finished parts still required some finishing with some files to get the right fit).Once assembled I ended up with a 3/8"-1/2" between the end of the adapter and the edge of the carb opening. I missed the chance to take photos of the assembly during the first mock up but the trimmed section of hose fit perfectly over the adapter and the carb. Should now be able to use two band clamps to secure it.





PLA plastic can supposedly handle fuel but this will also be tested once the bike is back on the road (prob. next summer, 41degF right now). I also plan on putting some pieces in gasoline during the winter to see what happens.

I just use radiator hose. Doesn't shrink.
Steve

Great idea! As long as the ID of your flange is the same or larger than that of the carburetor, it shouldn't have a negative impact on air flow, which may-may not matter much anyway.

IMO, SWest's solution is way too practical.

:whistle:

how did your invention work out? These things are freaking impossible PIAs on a 305. I bought the last pair on the continent years ago and they turned to rock in no time.

I've had my 305 for about a week and figured out a short-term solution - I bought some 2" filler hose (actual ID was over 2", so i cut and duct taped it to size; waiting on 1.75" in the mail to try) and then cut down the remnants of the original airbox boots. Carbs go on, hose goes on, cut-down boots press in from inside the airbox.

It seems to work okay for now, and I think that with intact properly sized hose and some custom (3d printed?) flanges for the airbox it's a viable option.

My skills of an artist are lacking but here's my idea. I'll update if I make it a reality.
 

I would love to get my hands on some 3d printed flanges, because the shop I'm taking my bike for the head gasket has heat shrink plastic they have used to replace boots in the past and they say it works great. But I would think you gotta have something for it to grip on the airbox side, and the flange would be perfect.

Thinking about it I suppose I could make  a pvc flange with some pipe and a slightly bigger pipe for a collar. Not sure how that would react with gas though. OK Doctor Google says that might not work so well

Had a eureka moment and found  this.  I think it's long enough - I just need about an inch past the airbox opening, since the hose going onto the carbs will have a 10mm gap once mounted (any longer and airbox needs to come out - done it twice, never again). 

Might be able to find something similar at an Ace or similar. I swear they should be sponsoring me at this point. 

It may be something you already thought of.
But could you run a long velocity stack into the airbox.
Put a small silicone coupler at the carb.
Silicone a rubber grommet around the stack to seal at the airbox so you could pull the velocity stack away for carb removal.

grommets
www.grainger.com/search/raw-materials/ru...ue&suggestConfigId=6
velocity stacks
www.efihardware.com/products/c166/Ram-Tu...ks-No-Base-air-horns
 

ghostdive post=846327Had a eureka moment and found  this.  I think it's long enough - I just need about an inch past the airbox opening, since the hose going onto the carbs will have a 10mm gap once mounted (any longer and airbox needs to come out - done it twice, never again). 

Might be able to find something similar at an Ace or similar. I swear they should be sponsoring me at this point. 

I like it.

wrote:

It may be something you already thought of.
But could you run a long velocity stack into the airbox.
Put a small silicone coupler at the carb.
Silicone a rubber grommet around the stack to seal at the airbox so you could pull the velocity stack away for carb removal.

grommets
www.grainger.com/search/raw-materials/ru...ue&suggestConfigId=6
velocity stacks
www.efihardware.com/products/c166/Ram-Tu...ks-No-Base-air-horns

 

I'm not familiar with stacks but it looks possible.