This isolator is installed in the pressure line between
the carb or fuel pump (where you normally pick up fuel pressure) and the
fuel pressure gauge. It has a diaphragm that prevents fuel from reaching
the gauge (inside the driver's compartment). The driver's side of the
isolator and the line to the gauge are filled with a fluid that transfers
the pressure to the gauge.
To install this isolator follow the steps here. It must be mounted in
the engine compartment at approximately the same height from the ground
as the gauge. A bracket is included. Make note of the normal fuel pressure
at idle. This will be used at the end to confirm that everything is working
- The rounded end of the isolator faces the gauge. Plan where you will
mount the isolator. It must be at the same height as the gauge. Drill
a hole in the firewall for the line from the isolator to the gage. Make
it just large enough to get the line nut thru. We strongly recommend
AN style SS braided steel lines and fittings. Use the correct length
line. Extra line coiled up will make it difficult to fill the system.
See the Longacre catalog for a selection of lengths. Use a grommet to
protect the line.
- Install the line from the isolator to the gauge. Run it thru the
firewall and install it onto the rounded side of the isolator with appropriate
- You will now fill the system from isolator to gauge with fluid. Use
a 50/50 mix of anti-freeze and water (don't use oil as it will not flow
properly and slow gauge response). The isolator came with a small plastic
bottle and a length of thin plastic tubing. Fill the bottle with the
- Disassemble the isolator and hold it so the gasket surface is level.
Insert the small tube into the hole and thru the line to the gauge as
far as it will go.
- Gently squeeze the bottle. Fluid will be forced into the line at or
near the gauge and force out trapped air. As soon as fluid comes out
around the small tube continue to gently squeeze the bottle and slowly
pull the tube out of the line. As you do this the line will fill completely
with virtually no air pockets.
- When you have pulled all of the tube out hold the isolator level and
fill the cavity to the top. Keeping it level place the orange diaphragm
on top with the raised rib facing down. Align the holes and place the
other half of the isolator in place. Put the bracket where it needs
to be and install the screws. Tighten firmly. Mount the bracket as planned
and connect to the carb.
- Start the motor and CHECK FOR FUEL LEAKS FIRST! Let the motor run
for several minutes to be sure there are none. If there are any leaks
repeat step 6 above and recheck for leaks.
- Check the pressure reading. If it is lower than before you may still
have air in the system. If installed and filled properly it will have
no affect on the pressure. Repeat the above procedure starting at step
4. When OK mount the isolator as planned. Check again for fuel and fluid
Spilled fuel on a motor is extremely
dangerous. It can cause fire which may result in injury or death.