Adding fuel capacity

Portable standby generator troubleshooting and repair questions. (Gasoline, diesel, propane, natural gas)
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Bigl62
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Fri Jul 12, 2019 11:32 am

Would like to add a boat gas tank to extend running time. Does the tank need to be elevated??
Can the tank be tied into existing fuel by drilling a hole through cover, if so where is the best place to tie into fuel line??
Chris
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Fri Jul 12, 2019 11:58 am

I think I would approach this a different way... Instead of trying to add to the existing tank with another fuel source, I'd cut a tee fitting into the fuel line to the carb and add a 2nd fuel shutoff to the secondary tank.

If you try and fill the existing tank from the new tank, it will overflow through the vent and cause issues. If you install the tee and shutoff, that would allow you to remove the secondary tank if needed and also would just add to the fuel availability at the carb instead of trying to re-fill the other existing tank (if that makes sense...)

I suppose if the other tank is much higher than the existing tank, it could fill from the bottom anyways, but would be less likely I'd think...
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ChrisMills
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Sat Nov 30, 2019 10:24 am

I've seen the added tank done a few times and it doesn't seem to work well. I've even done it myself a couple of times. Once with success and once without.

There seem to be a couple of issues in play. The first thing is that the fuel tank on the portables is very close to to the carb. The fuel line is kept as short as possible. You get internal resistance with a 1/4" fuel line. It's not a problem if it's only a few inches long. It becomes a real struggle for the carb to draw in enough fuel if the line is too long. You generally get very hard starts and the motor tends to cut out under load because it is starved for fuel.

The second issue is that boat tanks draw from the top whereas gen tanks draw from the bottom. It can be a real hassle to prime the line, then you have to reprime it every time you want to start the generator.

Elevation helps, but you need to have the tank about 2 1/2 feet above the inlet of the carb for every 1 psi of pressure you want. Sizing the fuel line up to 1/2" Inside diameter solves the resistance problem.

It's a judgement call on if it's worthwhile to work through the problems involved with sizing up the tank.
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