Intake volume

[Danappger]

Like to collect some thoughts on air intake volume. I'm the guy who put a KX100 engine in a powered paraglider (I'm still refining the design but the motor's working out quite well). Anyway, when I first set it up, I put a K&N conical air filter on the carburetor, sizing it according to engine displacement and rpm's per K&N's instructions. It ran like crap, bogged down around 8000 rpm's. With the filter off, it ran fine, right up to 12,000. Figuring it was too much restriction, and not needing much filtration in an aircraft application, I stretched a piece of nylon stocking over the carb inlet... and it still ran like crap. Surprising, since the nylon has very little restriction.

I then attached a piece of automotive radiator hose, about 8" long, to the carb, and put the same nylon stocking over the other end. Surprise... it ran fine that way. I haven't yet tried the K&N filter on the end of the tube. I'm guessing that having the volume downstream of any restriction is critical to getting it to run right... prehaps a pressure wave (similar to the tuned exhaust) is bouncing off even the flimsiest filter if it's too close? I'd go with an air box (intake silencer) like the kart guys run (and lots of paramotors have too), but I don't have the room.

Any thoughts on what's happening here?

-Dana

If aliens are smart enough to travel through space, why do they keep abducting the dumbest people on earth?

 

[QKENUF4U]

ya must be getting alot of turbulance without the tub there to help straighten the air coming into the carb body. try the k&n on the tube and if it works leave it that way.

 

[Danappger]

I don't think it's turbulence, since it works without the tube as long as there's no filter of any kind... I suspect it's some kind of volume or wave reflection thing.

I do intend to try it with the K&N on the tube when I get the time, though.

-Dana

We wonder why the dogs always drink out of our toilets, but look at it from their point of view: why do humans keep peeing into their water bowls?