YS-91AC Supercharged Four Stroke Glow to Gas Conversion

I’ve been thinking about this project for a few years. Recently, I spoke with a friend who had the same idea and it renewed my interest. The original concept was to somehow modify the existing fuel regulator to be compatible with gasoline. The YS system contains a fuel inlet “needle” which is made of silicone. Silicone swells in gasoline so this won’t do. Later, I had the idea that I could avoid the YS regulator by using Walbro metering components or a Cline Regulator. These are compatible with gasoline but not easily adjustable and I wasn’t sure what the fuel delivery would be like. Eventually, I settled on making a new regulator of the original design incorporating compatible materials and minor changes for fuel delivery. The regulator replaces the stock unit. Inside the engine silicone seals were replaced with Viton. The original check valve also uses a silicone flapper and was replaced.

The ignition system is typical with a sensor mounted on the front bearing housing and a ring with a magnet over the drive hub. A Rimfire 1/4″-32 spark plug was used. I decided to start with 16:1 fuel using SPL Avenger oil. This may or may not be enough oil and I won’t find out until I have a lot of time on the engine, or sooner. Fuel is VP Racing SEF 4-Cycle.

Finding the regulator setting to get the engine started didn’t take long. The needles were very sensitive, but this was expected. I may be able to make a change to the regulator to reduce the sensitivity. It tune well by adjusting all three settings, regulator, main needle, and idle air bleed. I shut it down and went for the camera. The engine refused run well and sometimes it wouldn’t start. It took some time, but when I needed to refuel I found the answer. Disconnecting the fuel lines I expected the typical tank pressure discharge, but there was none. The check valve stopped working, so I found another. The resulting video is a bit short because the camera was on for a long time and the battery gave up.

One Response to “YS-91AC Supercharged Four Stroke Glow to Gas Conversion”

  1. Aquaman Says:

    Nice Job.

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