weber: fuel return line and tank vent

[ant720]

Hey all,

 

I'm trying to wrap my head around the fuel system after replacing a newer fuel pump a PO installed.

 

Should I run a fuel return line with a weber 32/36 on a z24? I've seen mixed opinions. 

 

Second question(s), the fuel tank is not venting properly. When I remove the gas cap the tank is very pressurized. Why is this happening? I removed the check valve and was able to blow through both ways with a bit of effort, but nothing crazy. Should I replace the check valve? Did this pressure cause the fuel pump to fail prematurely/lock up? I also have the canister removed so the only thing b/n the tank and atmosphere is the check valve.

[G-Duax]

I run a return line on my 32/36 just to prevent vapor lock.

Buy another Weber inlet barb fitting, solder the end shut, and drill a very small hole through the solder.

I used a 1/16" drill.

Any vapor, or air in the incoming line passes through the small hole quickly, but fuel not so much.

 

And I run a vented cap on my 620.

Depending on big brother laws, you may not be able to do so.

(or run a standard cap when you get it inspected, then switch to a vented when you have passed.

[datzenmike]

Always run a return line. It constantly circulates cooler gas from the tank past the carburetor. This prevents vapor lock, which is the boiling gas in the lines or carb on very hot days making restarts easier. Constant circulation also filters the gas over and over keeping the tank clean. There is no down side to having a return line. Just use the 720 fuel delivery system changing only the weber carb. The return line is already there.

 

Pressure in the tank is unlikely. Where is the pump that would cause this???? Likely the sound you hear is air rushing in to replace the gas that was removed while driving. The tank vent line is plugged. It should go to the charcoal canister up by the rad. Hard line may be crushed somewhere on the frame or hose kinked or connected to wrong nipple on the canister. The check valve is only to prevent gas being expelled from the tank in a roll over. 

[ant720]

I'm having trouble adding pictures. But the current set up is the fuel line runs into the left barb of the 3 possible ports on the front of the carb. The bottom and right are capped off. So I should get another fuel inlet barb, install it on the right port and run a fuel line from that to the stock fuel return line?

 

I will also get a vented gas cap.

 

 

 

[Charlie69]

21 hours ago, G-Duax said:

I run a return line on my 32/36 just to prevent vapor lock.

Buy another Weber inlet barb fitting, solder the end shut, and drill a very small hole through the solder.

I used a 1/16" drill.

Any vapor, or air in the incoming line passes through the small hole quickly, but fuel not so much.

 

And I run a vented cap on my 620.

Depending on big brother laws, you may not be able to do so.

(or run a standard cap when you get it inspected, then switch to a vented when you have passed.

Hook the Weber to the factory fuel line connection that connected to the stock carb.  This is a "Y" pipe with a metered orifice in the return line that helps to maintain 3LBS fuel pressure the Weber requires. I always run stock 720 fuel pumps.  Use the throttle linkage bracket off of the factory carb on the Weber to connect the stock throttle cable.

 

 

 

This is not Rocket Science!

Edited September 2, 2018 by Charlie69