John Deere 720 Gas

pinman_87

New User
Been toying with the carb on a 720 gas. On top of the carb is a inlet vent that feeds back into the tank. Is this necessary? The rest of the carb is clean, but this area is collecting rust and i believe causing my problems. I didnt know if it was there for the auto shut off?(which i removed and put a manual one on). Thanks for your help.
 
That has to do with preventing a vapor lock. Somebody else may have more details. I played with one earlier this summer.
 
Without this tube and using the automatic shutoff, fuel would be trapped in the fuel line with the tractor shut down. Heat from the engine would expand this trapped fuel and the pressure would unseat the needle from its seat and flood the carburetor making for a hard hot restart. The extra tube gives the expanding fuel a place to go. Without an automatic shutoff fuel can expand back into the tank by the ordinary fuel line.
 
If i still ran the vent line on top of the carb, with a manual fuel shut off would it cause problems when operating?
 
The tube is not a vent line as the tank has a separate external vent line. The function of the tube is to prevent hot start flooding as described in my post below. A manual shut off valve would not cause any problems. However, be sure the separate vent line is open as the cap is not vented.
 

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