Subject: Re: Fuel Flow 101
Author: Bruce Giller
Date: Apr 11, 2003, 6:00 PM
Post ID: 1712589790
Keith,
I've got inline fuel filters on both petcock fuel lines before the
crossover. When I turn on a petcock (fuel filter empty), you can see
the fuel flow by and then fill the filter (there might be a tiny bubble
in there depending on the orientation of the filter) as the float bowl
fills up.
Have you tried hooking up all the fuel lines, turn on a petcock, and
then bleed gas out of the float bowl (just unscrew the 'cap' on the
bottom of VHB29's float bowl)? Gas should flow thru the line to fill
the emptying float bowl. This is just a test to see if gas is flowing
as gas is being removed from the bowl.
I think that your carb's vent holes are clear (is the level in the fuel
lines equal to the level of the gas inside the float bowl?) but somehow
the air remaining in the fuel lines is not going back up thru the
petcocks into the gas tank. No idea how this can happen since fuel is
coming down.
Have you inspected the petcocks by removing them from the tank and
seeing if anything is blocked?
Bruce
'72 Eldo
Keith Ruff wrote:
I need an education on how the fuel flow works from tank to carb. On all of the BMW's I had owned in the past, a fuel line from each petcock connected to a crossover, which then had fuel lines running from the crossover to each carb. This is the exact same set up on my 71 Ambo. I used to also run in line filters on my Beemers but have not done so on the Ambo. When I opened the petcocks on the Beemers, fuel would flow through the lines, down to the carbs, and fill all the way up back up to the petcock. There was fuel throughout the entire line, either when running or not running. The Ambo has got me confused. When I open the petcocks, nothing flows. I can see fuel in the lower lines just below the crossover, but the fuel will not fill the remainder of the lines. I just checked the petcocks, removed the hose from one side and put a test fuel hose on it and ran it to a container. Opened the petcock and fuel was a flowin'. Closed the petcock, let the line drain, then put my thumb on the end of the hose. Opened the petcock and NO FLOW. So it appears any air in the line stops the flow. I then tested the right side petcock while the left side was disconnected so air could escape and it flowed perfect, but gas would not flow when I put my thumb over the open end of the left side fuel hose. Can I deduce that the petcocks are not functioning correctly? Should the petcocks allow air pockets in the lines to escape up into the tank, or is that the job of the carbs? I squirted some carb cleaner into the carb vent holes but that did not change the situation, still no flow out of the petcocks when the lines were reconnected. Does this sytem not want fuel all the way up the lines to the petcocks, but rather just enough in the lower lines to feed the carbs? Does it let air escape through the carb vent holes when the carbs need fuel, thus letting fuel flow out of the petcocks? I am confused at the operation. I am not sure if I am worried about nothing or if I have a fuel flow problem. Please educate me. |