by Had Robinson
You are at launch and ready with glider overhead, moving in the right direction, and go to full throttle. Rather than surge ahead with power and away from the ground, the engine goes BLUB...CLUNK and everything stops DEAD. Your glider likely winds up on top of you and the motor. It is probably one of the most *annoying* and embarrassing events we motorheads experience. What happened?
These types of carburetors have (2) problems when going to WOT quickly.
- They have no fuel enrichment system that kicks in when full throttle is applied quickly as in automotive carburetors or in electronic fuel injection
systems. When the throttle plate is opened too fast, the air rushes into the engine before enough fuel can get moving through the various passageways and jets in the carburetor and then into
the engine. Consequently, the engine leans out and stalls.
- The Walbro fuel pumps were *NOT* designed to pump fuel from a tank 18"/45cm below the carburetor fuel inlet. All paramotor diaphragm carburetors were designed for obsolete chainsaws that had the fuel tank level with the carburetor.
Lack of fuel enrichment and a feeble fuel pump guarantee that sudden WOT will cause a stall. Pilots must be careful to always apply throttle slowly and deliberately when launching. Attention overload is very common when launching and pilots will jam the throttle unless they consciously tell themselves not to.
Why not install a fuel injection system on paramotor engines? It is impractical (even ridiculous) because of the of the number of things that must be monitored for it to work properly e.g. air temperature, air pressure, air mass going through the system, engine temperature, throttle position, exhaust gas content, etc. This is to say nothing of the electrical requirements (alternator and battery) etc. On top of this, the system must be programmed with a computer for each engine. I hope you get the idea....
Fortunately, Southwest Airsports is working on a fix for this called the FSM (fuel system modification) that eliminates this stall problem and dramatically increases engine power, among other things. It is simple, reliable, durable, and inexpensive. It should be ready by early 2020 for distribution through Miniplane-USA.