Howell 2-Jet Throttle

These are the throttle plans that are included in my V-Twin and V-Four engine plan sets. The photos and the drawings show the angled fuel inlet used on my V-Twin engine. There is also a drawing of the throttle body with the fuel inlet parallel to the throttle shaft which will suit most other engine types. Both configurations are included in the plans. It is small in physical size, very adjustable and not nearly as difficult to build as it looks. The configuration and size of mounting flange (or a spigot) at the base of the unit is easily modified to suit your engine requirements. The two threaded holes at the top are for mounting an air filter (included in the plans) if desired. Otherwise, a trumpet shape velocity stack may be used instead - or your own special treatment.

The through air passage is .250" in diameter. The throttle is large enough to operate engines up to 1" bore (25.4mm) and 1-1/4" stroke (31.75mm) with a provision for higher performance than I use on my V-Twin engine. This is the throttle recommended by Lee Hodgen for his radial engines up to and including his 9 cylinder engine and included with his plan sets under license from me. Multi cylinder engines don't need larger throttles than a single cylinder engine because the throttle only supplies one cylinder at a time and does nothing when there is no intake stroke demand on it. For larger or smaller cylinders the plans can be scaled up or down in size to suit.

The throttle has two fuel adjustment needles - one for idle fuel mixture and one for high speed fuel mixture. In photo #1 above, the fuel needle knob on the left is the idle mixture adjustment and the fuel needle knob on the right is the high speed mixture adjustment. Only one fuel inlet is needed to serve both fuel jets.

In Photo #2 the two socket head screws to the right of the high speed mixture adjustment are the idle stop and high speed throttle stop screws.

The throttle is .975" high including the mounting flange, and .925" by .765" excluding the fuel needles.

The plans set consists of 5 sheets of drawings plus a sheet of construction notes.

"The plans duly arrived by first post yesterday. What excellent service!  Thank you very much for your part." - Mike Durnford - Pembroke Dock, England