Bypass Block Off Plates

For fuel injection operation it is best to disable the bypass circuit of the carbs. The bypasses have long been a ZS carb trouble area especially while idling. Sticking and leaking valves allow too much air to bypass the throttle plate causing a lean condition. Fuel injected engines are especially sensitive to extra air causing a high idle. Installation of block off plates is easy and can usually be done in about half an hour. It can be done without removing the carbs using a stubby flat blade screwdriver.

The bypass valves are located on the forward side of each carburetor. There are three slotted screws that hold the bypass assembly in place. The Phillips screws need not be disturbed. A stubby screwdriver and patience is needed to do the rear carb.

With the bypass assembly removed you can see the gasket. Notice the cut in the gasket between holes? Even with the valve functioning properly air leaks through that cut.

Remove all traces of the gasket from the carburetor body.

Looking at the bypass valve with a gasket in place. No gasket is required when using the block off plate but it doesn’t hurt to leave it in place.

Block off plate in place ready to be reinstalled. No gasket is required but if it makes you feel better, a light wipe of Hylomar will ensure a good seal. IMPORTANT- the block off plate goes flat against the carb body without a gasket.