Rochester
4 Jet Accelerator Pump Problem

Rochester 4 Jet

Rochester 4G

Rochester 4GC Pump

This
article illustrates a problem one of our customers had with their
Rochester
4G carburetor
. Below is the question submitted following by
our answer. These type of problems are very hard to diagnose without
the carburetor being in front of us, but we do what we can.
Here
is a problem that I knew I had from tear down.  The first
slide shows the accelerator pump I removed and it was pretty severely
bent   The pump shaft and lever assembly seems also bent.
Shaft is clearly not parallel to the lever where it should be
and looks like a forced alignment to the pump stem.  Could it
be a wrong pump shaft and lever was wrongly installed?  Before
I order the one you show, I thought I’d ask about this first.
Straighten
the pump and install it into the carburetor. Don’t forget the return
spring under the pump.
Get the lever so that it pushes straight down on the pump. Adjust the
pump as per instructions in the carburetor kit. As per the instructions
the throttle plates will be closed. This gives you a starting
point.

 

When
you open the throttle, the pump should go down without any resistance
and you should be able to open the throttle wide open. If the pump is
too long, the throttle will not open all the way. Now when
you let up on the throttle, the return spring under the
accelerator pump
will push the pump up and return the throttle back to the closed
position.

 

Now,
the only way to be sure you have the correct accelerator pump is to buy
one based on the carburetor number, otherwise it is a guess at best and
you would have to try different pumps until you found one that worked.
The
diameter of accelerator pumps vary also, which makes this situation
even more difficult.