Subject: RE: Stupid newbie question #1, petcocks
Author: Greg Bender
Date: Jan 25, 2005, 3:16 PM
Post ID: 1718272832
If you are lucky, AJ, you have either one of the two common petcocks
that Guzzi used. One type is chrome plated, and the other type is
alluminum. Both have square bodies and with a little handle/lever that
turns. Now, on to how most of them operate...
When functioning properly (that is, no leaks), the petcocks I described
above are either "on" or "off". There is no "reserve" position (more on
reserve, later). If all is right with the world, the 6 o'clock position
should have the fuel moving through either petcock. Either the 3 o'clock
or the 6 o'clock positions will close the fuel supply.
About reserve...later models (starting with the 850T, I think) used
petcocks with three handle positions "on", "off", and "reserve". Moto
Guzzi used a different technique with the loop frames. Essentially,
there is a tube that is affixed to the top of each petcock (stuck up
into the tank). The tube is perferated with holes so that the fuel can
flow. On the left petcock (in the stock configuration), the holes in the
tube did not start until part way up the tube. On the right petcock (in
the stock configuration), the holes in the tube go clear to the bottom.
The idea being that you turn the left petcock on and run the bike. Once
the fuel level goes below the perforations on the tube, you turn the
right side petcock on and beeline for the nearest petrol station.
This design requires that you have a "cross" installed between the fuel
lines so that one petcock feeds both carburetors. As Patrick mentions,
there are many aftermarket varieties that have been installed on a lot
of the loops, so you really don't know what you have until you take a
look.
To the best of my knowledge, the above information is correct. However,
the wise members on this list will certainly correct my errors. Good
luck!
Patrick Hayes wrote:
AJ Huff wrote:
Guzzi used several types of petcocks and some owners also changed to aftermarket versions. So, it is really difficult for anyone to answer this precisely for you. You'll really have to drain the tanks down to analyze what you have. Some petcocks have two internal stems. One sits higher than the other. When fuel level gets below the higher stem it stops flowing. Turning the valve opens the lower stem for an additional or reserve supply. Some petcocks only have one flow level. You drive the bike on one until it runs dry. Due to the internal shape of the tank there is always an extra supply captured on the non-opened side. Open the second valve and you use that supply as a reserve. Pull your petcocks, disassemble and learn what you have on your bike. Generally, the bikes will run just fine on only one petcock opening unless you have some other fuel flow restriction. Patrick Hayes Fremont CA |
Regards,
Greg Bender
1971 Ambassador
2000 Quota
http://www.thisoldtractor.com/gtbender