I'm building my first airplane with a cowl (Goldberg Cub). Up until now it's been .40-size 2-stroke engines out in the open-nose breeze, but this time I'm trying to stuff an OS 4-stroke inside the kit's vacuum-molded PVC cowl.

The engine/mount seems to fit on the firewall OK, and when I work up the nerve I'll start cutting away the plastic to clear the cylinder head. But the 4-stroke's needle valve will be buried deep inside the cowl, facing down.

How do you guys get at the needle valve on these cowled engines? Do you shut it down and pull the cowl off every time you want to change the mixture? Do you figure you'll get it set right on the test stand, and then just leave it?

Norm from New England

Hi Norm,

What I, and most people that I know do in a situation like yours is to attach an "L" shaped extension to the needle valve.
The extension shoud just stick out of the cowl, and by virtue of it's shape, you can easily tell how many turns you've made on the needle.

This extension can be made from excess push rod wire, and attaches to the top of the needle by means of the embedded set screw in the side of the needle.

I do not have any pictures on hand, but I am sure someone here would.

Good Luck

The two most common approaches are either the use of a wire extension thru the cowl or my preference is to adapt a socket head capscrew to the end ot the needle valve and then use a ball driver wrench to adjust the needle thru an access hole in the bottom of the cowl. The last method allows the cowling to be removed without having to remove the needle valve and wire extension.
Also four strokes as a class require very little adjustment once they are broken in. Only extreme temperature or nitro content variations will cause the need for adjustment.

And if you can flip your engine over so that the needle is on the top instead of the bottom it'll make life a lot easier for you.

Dave

Some O.S. 4 stroke engines will allow the carborator to be reversed so the needle valve sticks up, instead of down (side mount) or out the left or the right (upright/inverted). Make the hole in the cowl big enough so the needle and extension can be inserted after the cowl is mounted. More difficult, is the choke control. This exact topic is being descussed in the beginners forum, as we speak!

I do the 4-40 screw in the needel like Gremlin said but take it one step more. I use A fired 22 case and drill A hole in that too and screw it down with the 4-40 screw. Then when the engine is running it just makes it easy to get the ball wrench into the screw head and stays there.
Once my four strokes are broken in and set I never have to touch them unless I go to A different size prop. If it's cold enough to have to adjust them then I'm not flying that day!!!

I use the Allen wrench that comes with my engines.

Hi Norm,
Here is a pic of what Ejiro was referring to about the "L" shaped extension in a two stroke engine mounted on it's side.

Do like Mode One said. Just take out the two screws that hold the carb on and flip the carb over. They are designed to do that

Thanks guys!

I'm not sure exactly how you are attaching allen-head bolts to your needles, but I'll have to go home and check the engine. More than one suggested it, so there must be some way to do it short of spot welding...

The choke plate has a hex head milled on to the end of it's handle, so I guess they intend you to stick a nut wrench through the cowl. (Insert "nut-wrench" jokes here.)

RC Universe is amazing: tons of modeling experience, and great people happy to share it. Thanks guys!

Norm

Here's how: