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Thread: Vapor Locking?

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    Moderator WillWagner's Avatar
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    Default Vapor Locking?

    A guy I know has an AM General made A2. He took it out to the desert last weekend and after 3 or so hours of trail riding, it started to hesitate and eventually stopped running. He removed the plug on the bottom of the carb and some chunks came out, re started it, drove a bit and it started doing the same thing. When he removed the inline fuel filter that was installed before the inlet to the carb, fuel shot out of the line, it re started and did the issue again and this time when he removed the plug in the bottom of the carb, nothing, then fuel came out under pressure.

    I looked at it after he got it home....it was driven to me, so I don't think it is a carb issue and the oil was not over full or didn't smell of gas. It is an A2 with some of the emission hoses removed, well, the two from the air filter and the 5/16 one coming out of the fire wall to the filter. I have not really worked on one of these, but if the line coming thru the firewall is a vent that goes to the the air filter from the tank and it is plugged, could this cause an issue that seems like vapor locking? Pressure and sucking a vacuum in the tank?
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    I had a similar thing happen on my 151 and my grandfather on his m3 half track. All of my 151s don’t have return lines or anything besides the feed line and some sort of tank vent. Both times we wrapped the metal feed line with tin foil and it quit vapor locking, so maybe give that a shot as a temporary fix if it’s caused by heat under the hood. The fuel cap could be a vented cap or try cracking it open a little and drive to see if the issue still happens.

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    I have a M37 that did that from time to time and I put a elec. fuel pump on it and that helped a lot.
    You could cover the filter and fuel lines with some heat ref. tape.
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    The issue sounds like a delivery problem and not a carb issue, I never saw it happen. He bought a carb kit from TNJ. Maybe we'll rebuild it since crap came out the bottom and try heat tape or rubber hose around the lines under the hood. He has the stuff to hook the vapor recovery up, maybe we will do that too.

    Thanks guys
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    You might want to check the ignition coil.

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    All that is new too, last time he took it out the rotor ans pick up shorted out and burned the coil up.
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    OK, an update. The owner bought a kit from TNJ Murray. It was a great kit, had everything but the bowl and pump screws! Took the carb apart, it had old gas in it at one time, so lotsa gunk in it, cleaned it out. Checked the float level, WAY low. Set that, bolted it up, started up great. Set the idle adjustment, seemed good. Let it sit a bit and in the meantime, figured out the emission line routing. While messing with the lines, I disconnected the line that goes from the fuel inlet, the fitting is orificed, and goes back to the tank. I THINK it is because the pump is capable of more pressure than the system needs, so, it shunts fuel back to the tank thru the orificed fitting, back to the tank, but that is just a thought. When I removed the line, after sitting 10 mins, there was still a boat load of pressure in it!. Blew back into the tank, nope, plugged solid. Pulled the soft line, clear, traced the line to the tank, pulled that, a giant glob of goo lodged in the line! Blew that out, pulled the fitting, that too was plugged. Cleaned it, re assembled and it still runs good, but we will need to see what happens after a 3 hr tour in the dirt with it. I think I got it licked though.
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