velocity stack for walbro
 

I have an SPE40 that runs like a scalded dog with the cowling off but with the cowling on, there is not enough air for the carb as it is too close to the cowling. I know I can just grind a nice hole in the cowling but it might look better with a velocity stack. I can go the home made route with brass tubing, if I can get it that big, and thread a plate on the carb so the stack can be installed after the cowling. can someone come up with a better idea?

RE: velocity stack for walbro
 

I was taught you need at least an inch clearance from air intake to cowl in order for a side-intake engine to breathe well. If you don't have the inch, then you need a breather hole in the cowl. If you get the Great Planes stack (aluminum tube with angled end), you can cut the end of the tube so it extends almost to the cowl, but still short enough for the cowl to slip right over it. (You don't really need the angled end.) That way you can still get good breathing, and you can choke with your fingertip instead of the choke plate. Nothing chokes like a fingertip, plus you can feel the wet gas so you know you're drawing fuel.

RE: velocity stack for walbro
 

I probably have 1/4 inch or less. close enough that I had to cut a hole in the cowl at the field for the choke arm screw to clear. My engine guru said to just cut the hole and not waste my money on the stack. I just think the stack would look better than a gaping hole in the cowling. thanks for the info.

RE: velocity stack for walbro
 

How about making a baffle to funnel air to the carb?

RE: velocity stack for walbro
 

If you are just a quarter inch from carb to cowl, then probably your idea of installing the stack through a hole in the cowl is a good way to go.

RE: velocity stack for walbro
 

Been there done that. Believe your engine guru as the hole in the cowl for your size carb does not have to be a huge one, say about 3/4"dia. Just make it nice and round.

Karol

RE: velocity stack for walbro
 

I think that is what I will do to start out. Later when I can get to a plumbing supply house, I'll find a piece of threaded 1" brass tube and thread it into a brass plate that fits behind the carb bolts. That is if I can find someone to tap threads in the plate. the commercial ones would be too hard to use and get the cowling on. the plane is a 105" wingspan JN4 "Jenny". I may make a fiberglass scoop to cover the hole like they use on car hoods. I could probably use a thinwall PVC pipe elbo sliced off. I think monokote will stick to pvc and I have a repair piece that came with the plane.

RE: velocity stack for walbro
 

free flow needs only 1/4 of the carb diameter for distance. so 1/4"would be enough for a 1"carb. It may get smaller than that before you run into trouble.

RE: velocity stack for walbro
 

Brillelli sells them

http://www.brillelli.com/index.html

They're listed under accessories.

RE: velocity stack for walbro
 

Or simply slice off an appropriate section of a small plastic soda bottle and there ya go.

Karol