Choke fault on newer Top 80 models
by Had Robinson
updated February 8, 2022
Newer model Top 80's (around and after 2020) have some changes, one of which can make the engine difficult or impossible to start when it is cold and requires full choke. It involves the choke setup on the new Flex Cage frame which prevents the choke from closing fully even though the pilot pulls down on the choke control as far as it will go.
On the new Flex Cage, the choke control (white arrow) has been moved to a new middle strut (green arrow) that is joined at the top to the rear strut (red arrow). The blue arrow points to the front strut.
The original frame has the choke control (white arrow) mounted to the front strut (green arrow). The rear strut (red arrow) is joined at the top to a 4" (10cm) horizontal tube that is connected to the front strut. The length of the horizontal tube allows a greater radius in the bend of the choke control so that it will function smoothly and completely close the choke, when needed.
Because the top of the choke control was moved much closer to the carburetor on the Flex Cage, there is a very sharp bend in it as it turns from the vertical to the horizontal. This bend acts like a spring so that when the choke is fully closed, it springs back enough to open the choke as shown in the photo below.
When the choke is open even a little, it will not allow a vacuum to be created on the metering lever diaphragm which, in turn, will prevent enough fuel to enter the engine so it will start when it is cold. The white arrow points to the choke control mounting flange on the Flex Cage.
The fix requires that the pilot move the upper mount (white arrow) of the choke control down enough (green arrow) in order to relieve the sharp bend. The only way to mount the upper choke control is to use a 10" zip tie (green arrow) wrapped 3X around the rear strut. It must be wrapped multiple times or it will slip out of position. This fix lowers the choke control and holds it firmly to the rear strut. It also allows the choke to move to the fully closed position – and stay there. It is impossible for a pilot to hold the choke fully closed, then pull on the starter and regulate the throttle. This is why the choke control must hold the choke at any position.
After moving the choke control down, the choke will now hold in the fully closed position.
Once this is done, a cold Top 80 engine will start easily when it is primed and choked.