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Poor Man's Air Restrictors

E

EmmCee

Forum Apprentice
Hey all. Thought I'd share a quick and easy mod I did on my '82 GS650E yesterday.

I run pods and as we all know the BS series carbs, being CV carbs are finicky, at best, with pods. I know one of the members sells an official version of this, but money being tight and I ever being one to tinker thought I'd give this a try. I also have a 3D printer, so I had nozles laying around.

What I did was take some of these 3D printer nozles:

https://a.co/d/07SwnidP

Put them in my drill, threads facing out and spun them up against a diamond file until they were cut down to just a hair over 4.5mm, slightly tapered, then tapped them into my carb like shown in the image below. I used 0.8mm nozles and they seem to have worked beautifully. Ill be experimenting going both up and down a size to see what my bike really likes and I will report back.

20260412_000942.jpg

Once I find that goldilocks size ill be tapping that port on my carb so I can thread them in with a little teflon tape on the threads.

Essentially, a poor man's air corrector.
 
Cool idea. I have a bunch of old mk8 nozzles lying around, but I already bought a set from zed. You could ask him what ID he uses for the BS to try to get a baseline!

Link to his big thread about them

IDK for certain, but I feel like the nozzle shape could really mess with the airflow but I'm excited to hear the results
 
I've always held the believe that the CV carbs are sensitive to turbulence, which the pods create aplenty.

Not to get too technical about the aerodynamics but basically the turbulence will create lower pressure on the outside perimeter of the carburettor ID vs the inside (core) of the airflow. Also the actually pressure anywhere is continuously fluctuating. The vacuüm (lower relative pressure) port to the diaphragm is on the outside perimeter of the ID of the carburettor...do you see where this is going? It is not receiving the same pressure as the bulk of what is going through the carburettor.

By installing an extender piper to the carbs first and then adding the pods to the ends of said pipes you'll calm the air (Reynolds number) a bit and help the CV carbs do its thing. Bonus points if the extender pipe is slightly trumpet shaped like a velocity stack. A straight pipe introduces turbulence by default because of the sharp edges.

The stock airbox and filter Create loads of turbulence as well, but the volume of the airbox and the velocity stack shaped intake rubbers allow the air to calm down and the pressure profile to equalize before arriving at the carburettor entrance, hence allowing the CV carbs to function properly.

The problem does not lie in the pods, but in the distance between the pods and the carbs.

Anyway...my 2 cents dealing with pod filters.
 
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