Throttle Body Injector Installation

IMPORTANT: Now is a good time to either run the carburetors dry or pull the drain plugs and drain the float bowls. Failure to drain the bowls will cause extreme flooding at start up as fuel will be supplied by both the injectors and the unrestricted jets. Once running as a fuel injected engine, the carb’s fuel passages are no longer used and float bowls do not contain any fuel.

One (1) TBI Adapters per Carb ZS 175 CD model shown

Installation of of a GM Throttle Body Injector (TBI) into the conversion insert is straight forward. This page shows the compact injector but the same principles apply to the larger bodied GM injectors. The injector pictured is the very common GM #5235277 used in 88 and 89 Chevrolet trucks.

The red arrows indicate where o-rings seal against the injector. Use a little automatic transmission fluid to lubricate the o-rings. It is nearly impossible to insert the injector without lubrication.

An o-ring resides in this groove and is installed onto the injector with lubrication. No sealant is used on the o-rings.

Looking down into the injector pocket you can see that the black small lower o-ring is in place. Be sure it is down into it’s pocket before attempting to insert the injector.

Once the o-rings are in place and lubricated, insert the injector with a twisting motion. It should stop with the top edge just proud of the aluminum pocket. Slip the half moon shaped retainer in place (it doesn’t matter which way it faces) and tighten the two button head screws with a 1/8″ Allen wrench. Before final tightening, align the injector in whatever direction you desire.

The insert is held in place in the Zenith Stromberg carbs by four stainless steel Philips head screws. No gasket between the insert and the carb body is required. BE SURE THE INJECTOR NOZZLE POINTS TOWARD THE ENGINE! The hose barb accepts a 5/16″ hose and you should try to use fuel injection type hose clamps. Typical fuel pressure is 12psi but some have experimented with these injectors near thirty psi. Needless to say keep an eye on the new installation for possible fuel leaks.

NOTE: Atop the insert is a 1/8″ brass pipe plug that is used to cap off a drill passage used during machining of the insert. The internal passages within the insert are large and it is doubtful they would ever become blocked but if need be, the brass plug can be removed with a 3/16″ allen wrench.

Although not required for operation, a modified dome can be installed to hide the TBI installation. On the bottom, the tube that is used to guide the piston needs to be completely cut away making the dome unsuitable for future use as a carb part. Around the bottom edge of the dome is a lip that should also be removed. It can be cut away with a Dremel tool, hand file, or by sanding it away on a flat surface. Additionally the top may need to be trimmed another half inch or so and the old plunger tube cap glued in place if under hood clearance is tight. Be sure to check the clearance before slamming the hood! Email me if you have questions about the domes.