Model A speedster to start. Two gas tanks.
Gas tank A in rear of car, bottom hose.
Gas tank B in front of car, top hose.
Third hose through firewall goes to carb.
Both tanks at about the same height.
Flow test: Flow measured at end of the carb line. Both tanks have gas caps on tight.
Pinch off bottom hose. Checking flow of front tank. Good flow.
Pinch off top hose. Checking flow of rear tank. Good flow
Open both lines to check both tanks flow together. Flow starts out good but continues at a glub glub of starving for air and a weak stream. Can hear the starving for air in front tank.
With both tanks flowing together there is a venting issue that I don't get if I run one tank at a time.
Any ideas to solve this fuel system venting issue? I want to run both tanks at the same time rather then having a tank sellector switch.
Are the caps vented? If so, are the vents clear? Some bugs like to plug small holes with mud.
Are the vent holes in the gas caps blocked ? Need to be open.
Did you verify the venting issue by removing both tank caps and the retesting? And then as the others said is the vents in the caps clear.
The rear cap is vented for sure. Not totally sure of front. However, when both tanks checked seperately, with caps on, each flow was satifactory. The venting issue only occures when both tanks are checked together.
Tyrone, try what Chad suggested. That will tell you one way or another if it is a venting problem. Dave
Is the level of the two tanks equal? If it is not, the fuel is too busy trying to equalize the tanks, to supply the carburetor. It just flows right on by.
OK, I believe I figured it out. Thanks to your help. I believe Ed's theory is valid and could be a very possible possibility. I can curtainly see that happening if the two tanks did not have time to equilize. However, I believe this is a case of a cap vent issue. Upon further investigation, I find the cap that I got with the tank is a radiator cap and thus is not vented.
I feel stupid for posting today. But for the knownledge of others, what I found. I did not notice the cap i got with the tank (bought at swap) was not a gas cap but a radiator cap one I do not know from what type car. Being a rad cap, there is no vent holes.
Two, the rear tank cap. I installed a new rubber gasket I got from the hardware store. The new gasket covered by half the vent holes inside the cap. Cutting the venting by half once screwed down.
So drilled vent holes in the one cap, and relocating new holes in the other solved the issue.
Thank you all for your help. I should pay attention to details more closely.
Tyrone, if that new gasket is indeed rubber, you may have some problems with gas softening it. If so, you could make one from heavy gasket material. Just a heads up. Dave
Thanks dave. Yes they are rubber. Will look to replace then soon.
Tyrone, Don't feel stupid, sometimes we get so wrapped up in a problem we overlook the obvious. A fresh set of eyes on the problem is always a good idea. Glad you got it figured out. Feel free to post anytime.