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Old 12-02-2012, 07:26 PM   #1
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If RV sits, fuel drains back into tank?

Ok, so one thing that I noticed today before I bought the motorhome was the fueling issue. He said the RV had not been started in a couple weeks, and that the fuel would "drain back" into the tank if it sat.

So he took off the cover and sure enough the fuel filter was completely dry. He poured a little fuel into the carb and it fired right up, and once running the fuel filter filled right up. It sat and idled perfect for 30 or so minutes while we looked the rig over, then we drove it down the hill put 100 bucks of gas in it and drove it back up the hill with no issues.

But what would cause this drain back in the first place? My first thought is there has to be a leak somewhere that's allowing air into he system.
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Old 12-02-2012, 07:41 PM   #2
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What make, model, year and what motor is the RV.
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Old 12-02-2012, 10:07 PM   #3
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Well now that you have bought the motorhome, you will have some time to diagnose the problem. I believe you must have a mechanical fuel pump as an electric one, would fill the filter etc when you turn on the ignition. Air can of course get into the system and cause the problem. one often overlooked contributor to air being introduced (especially when the vehicle sits) is fuel evaporation in the carburetor bowl. As the fuel level goes down due to evaporation the needle valve will open and admit air into the fuel lines. Normally the fuel pump would prevent fuel draining back into the tank as there are check valves built into it. It may be as simple as replacing the fuel pump. Hope this helps.
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Old 12-02-2012, 11:16 PM   #4
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If it really becomes an issue, replace the mechanical fuel pump with an electric one. Having to remove the engine hump and pour gas could get old.
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Old 12-02-2012, 11:28 PM   #5
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There is a check valve on GM carbs between the inlet fuel line and the carb. That may be bad. Easy fix.
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Old 12-02-2012, 11:49 PM   #6
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easy fix is to install an electric fuel pump back at the tank pushing the fuel to the mechanical pump.
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Old 12-02-2012, 11:55 PM   #7
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I have found with just about everything I own with a carburetor that today's fuel seems to evaporate really fast. My Jeeps do it, the RV does it, my motorcycles do it.
I have an electric pump on the frame rail near the tank, and a mechanical on the engine. Since the electric pump is controlled by an oil pressure switch it doesn't run when you are trying to start the motor. To avoid the long cranking required to get fuel in the carb I wired in a spring loaded toggle switch so I can turn the key on, hold the switch that will then run the electric pump, and then start. Now it will start with a couple seconds cranking instead of what seemed forever. And as soon as I let go of the switch the pump gets controlled by the oil pressure switch again for safety.
Today's fuel just doesn't play so nice with carbs....
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Old 12-03-2012, 10:36 AM   #8
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If the filter is empty there is something very WRONG

Most likely a check valve in the fuel pump.

But if a leak instead will be bad idea to add electric pump at tank, what was operating at vacuum is now under pressure and a pinhole is now a fire risk.

Fix what is broken first
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Old 12-03-2012, 11:02 AM   #9
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My Southwind came with the electric pump as original equipment along with the mechanical. It also has 1/2 inch fuel lines. Apparently it is supposed to help with vapor lock.
So having an electric pump isn't anything strange. I have multiple vehicles with carbs that if they sit for a couple weeks will all do the same thing. So they "All" have bad check valves, pumps, or leaks? I doubt it....
My vote is still for today's fuel just evaporating quickly.
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Old 12-03-2012, 05:19 PM   #10
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Quote:
Originally Posted by TQ60 View Post
If the filter is empty there is something very WRONG

Most likely a check valve in the fuel pump.

But if a leak instead will be bad idea to add electric pump at tank, what was operating at vacuum is now under pressure and a pinhole is now a fire risk.

Fix what is broken first

Agree, This morning I went to pick it up, so it had sat overnight, It took about 4 minutes of pumping to fire off the RV. After that, the starter would not even spin the engine once and it was running.
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