QuestionI'm having a problem with my petcock. It only lets fuel flow from one of the outlets and sucks through the other outlet. I have the tank off and I put some clear hose on the outlets to watch the flow and there is a lot of air in the lines as well. Its does this same thing if the cap is open or shut so I don't think its the vent hole. Also if you plug the line that is letting fuel flow, it pulls fuel back up that line and then starts letting fuel flow through the other line. Its like a siphon from one outlet to the other. I have cleaned and blew out all the holes on the petcock twice now and its still doing this. Any help would be great, Thanks Doug
AnswerDoug, I always use a small drill bit and turn it by hand down each of the passageways, so that can see the end of the bit when I look down one of the other passageways. Scale and varnish can build up in there causing restrictions. So, be absolutely sure that the passages are all cleared to normal sizes. Be sure that the same applies for the tube and the hole at the base of the petcock for the inside of the fuel tank. Do check the vent hole in the cap for blockages, so you don't experience fuel starvation when running.
Once that is all done and you are sure that those parts are all good, check the carbs. Float level is 21mm, measured at the furthest distance from the carb body to the float edge, with the float tang just resting in the float valve's spring-loaded needle end, NOT collapsing the tip. There is also a bowl vent for each of the carb bodies. High up on the carb body, there is a small protruding part which vents the float bowls. That fitting must be open to allow equalization of the fuel inside the bowls, when the engine is running. The passage to the vent is from the roof of the carb body in the bowl chamber. You could also have some debris backed up behind the float valve seats, causing imbalances in the fuel flow through the system. Everything has to be clean from gas cap to float bowl.
A few air bubbles in the lines is somewhat normal. When the float valves are open, a bit of air can go up the line, until the bowl fills and the valve shuts off again.
Hook up everything, once it is cleaned and pull the float bowls once the fuel has refilled them. There should be equal amounts of fuel in each bowl after a minute or so. If so, then don't worry about the air bubbles in the lines.
This is not uncommon with dual carbs and twin fuel lines coming from these kinds of petcocks. Be sure that the float levels are set, all jets and passageways in the carbs are clear, ignition timing is correct (affects fuel metering because of the vacuum signal produced at various timing settings) and that the engine has good compression on both sides.
Bill Silver
