Chris,
Without having disassembled one, I can't be sure, but as I understand them,
the Toronado w/A/C fuel pumps' return lines are merely another output port
with a small orifice to pass only a little fuel (but a lot of vapor if
present). If that's true,
a ruptured diaphragm would still allow fuel into the crankcase.
Another note: Early in my GMC ownership, headed west over the Rockies and
to Alaska, I was concerned about vapor lock, so installed a Carter 4070 as
a booster pump. Approaching the E. entrance to Yellowstone NP, I turned on
the booster. At the service station just inside the park, I noticed fuel
pouring from beneath the right front of the coach. Not wanting to burn
down the whole place, nor work on the coach there, I drove to the nearest
wide shoulder of the road and checked the problem.
Fearing the ruptured diaphragm problem, I'd run hard lines to a tee just
before the carburetor. Expecting the mechanical pump's output valve to be
a sufficient check valve, I included no other.
The top dome of the mechanical pump was where the leak occurred.
Surprisingly, my spare parts box contained a suitable plug to put in the
mechanical side of the tee. Disconnecting and plugging the input line to
the mechanical pump left that now piece of junk trying to pump air for the
next 9,000 miles of the trip.
Back home, I went to my current electric pump per tank with no selector
switch and have used that ever since. Unfortunately, I used one of the red
Holley's and it later "melted down" -- literally. I've had no problem with
the replacement 4070. Partially because of the Yellowstone problem, I do
have the 4070's tee'd together with inline check valves. If I have to
replace one on the road with "just anything", I don't want to have to worry
about whether that replacement will backfeed.
HTH someone.
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI & EBL,
Manny Brakes & 1-Ton, etc., etc., etc.
www.gmcwipersetc.com
On Tue, Dec 27, 2016 at 3:17 PM, Chris Tyler
wrote:
> To clarify: The mechanical pump, a booster pump, or replacing with
> electric?
>
> There is a prior thread about a replacement mech pump that has a return
> line that is supposed to help with vapor lock
> ...
> My .02 on electrical pumps: THe carter low pressure pumps seem to work out
> better on RV applications. Whn I was a tech, many OEMS were using Holly
> red or blue pumps, and had to change many out
> ...