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Lawn mower fuel tank mod #5431326 05/17/20 11:36 AM
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Avery4 Offline OP
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Hello everyone, I modded my Briggs powered mower's fuel tank before I mowed my lawn yesterday and I thought I'd share what I did with everyone. I had a few problems with the stock setup, so I figured I'd fix it. The number one problem I had with the stock setup was that the gas cap rattled loose from vibration. It isn't a regular threaded cap that can be tightened down good, it is one of those quarter turn non locking caps that fits quite loosely and frequently rattled loose from vibrations. The cap rattling loose and causing fuel to splash all over the hot engine clearly isn't a good thing. This is the main reason why I did this mod. Also, since the cap fits loosely, some fuel always drips out from around the cap down the tank onto the deck while its running if I fill the tank more than about 3/4 of the way. Not a whole lot, maybe a couple tablespoons of gas every time I mow.

What I did is I took the fuel tank off an old Tecrapseh mower with a blown engine and put it on my Briggs mower. This is a much better tank because it has a screw on cap that can be tightened down good and absolutely will not rattle loose. The "problem" is that it wasn't a direct swap because the mounting points are different and the fuel line connection comes out in the wrong place, so I had to get creative.

What I did is I used self tapping screws to secure a sheet metal rectangle that I cut out to the handle bars to make a shelf to put the tank on and I drilled holes in it to use zip ties to secure the tank to the shelf I made. I then removed the stock tank and ran a fuel line from the tank to the carburetor and secured it with zip ties. I angled the shelf forwards slightly so the fuel flows towards the engine.

This setup works great! The cap didn't rattle loose while I was mowing and not one drop of fuel splashed out even though I filled that tank about 1 inch from the top. The fuel also stays much cooler because it is no longer sitting 1/2 inch away from the hot engine. This means (slightly) better engine performance and significantly less evaporation of the fuel. Who knows, the EPA may start requiring mowers to be sold this way to reduce emissions from fuel vapors LOL

[Linked Image]

Last edited by Avery4; 05/17/20 11:37 AM.
Re: Lawn mower fuel tank mod [Re: Avery4] #5431338 05/17/20 11:51 AM
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CharlieJ Offline
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Looks like the same engine that’s on my lawn mower. (I increased the RPMs to 3600) You may have just needed a new gas cap.


'07 Mazda3 2.3 : Shell Rotella Gas TRUCK 5w-30
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Re: Lawn mower fuel tank mod [Re: Avery4] #5431353 05/17/20 12:08 PM
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skyactiv Offline
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Wrap a cold water soaked white towel around the fuel tank to see if that further helps the performance.


Wife: 15' Audi A4 quattro 6 speed manual
Me: 18' Elantra Sport 6 speed manual
The rude guy that points out reality


Re: Lawn mower fuel tank mod [Re: Avery4] #5431373 05/17/20 12:28 PM
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qjohn Offline
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It shows a lot of resourcefulness to make it work with what is already on hand!

However, from an engineering standpoint there looks to be a lot of things that can go wrong. I'd be concerned with the vulnerability of the fuel line, whether the tank could fall off, general fire safety.

I would recommend not modifying the fuel system, and just fixing the leak from the cap. If one feels they must change anything on the fuel system, keep the tank low and as far away from the operator as possible!

Re: Lawn mower fuel tank mod [Re: CharlieJ] #5431374 05/17/20 12:29 PM
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Avery4 Offline OP
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Originally Posted by CharlieJ
Looks like the same engine that’s on my lawn mower. (I increased the RPMs to 3600) You may have just needed a new gas cap.

Does your gas cap fit tightly or is it so loose you can take it off with 2 fingers easily? Or does it somehow lock in place?

Re: Lawn mower fuel tank mod [Re: Avery4] #5431376 05/17/20 12:38 PM
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mk378 Offline
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I did something similar on mine using a 1 gallon gas can with a barbed fitting tapped into the bottom. The vinyl fuel line does look sketchy. Use rubber fuel hose instead. A shutoff near the carb is very useful.

Re: Lawn mower fuel tank mod [Re: skyactiv] #5431377 05/17/20 12:38 PM
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Avery4 Offline OP
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Originally Posted by skyactiv
Wrap a cold water soaked white towel around the fuel tank to see if that further helps the performance.

It doesn't really matter a whole lot. Last year I filled an empty 1 quart oil bottle with gas and put it in the freezer to get it as cold as possible and I didn't really notice a whole lot, but this mower didn't lack power to begin with so not a great test. I will try that experiment again one of these days now that I have a tach and see if my water pump can reach a a higher RPM wide open under load with ice cold gas. It's basically a crude dyno, I circulate water and run it wide open and see what RPM it will reach. Normally it will hit 5200 RPM, but if I make a change that causes it to gain or lose power the RPM will increase or decrease.

Re: Lawn mower fuel tank mod [Re: qjohn] #5431379 05/17/20 12:43 PM
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Avery4 Offline OP
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Originally Posted by qjohn
It shows a lot of resourcefulness to make it work with what is already on hand!

However, from an engineering standpoint there looks to be a lot of things that can go wrong. I'd be concerned with the vulnerability of the fuel line, whether the tank could fall off, general fire safety.

I would recommend not modifying the fuel system, and just fixing the leak from the cap. If one feels they must change anything on the fuel system, keep the tank low and as far away from the operator as possible!

I understand what you are saying, it is very important to always put safety first. However, I don't see the tank randomly exploding or something while the way it was easily could have caused a fire. I do agree that the fuel line could be better protected though.

Re: Lawn mower fuel tank mod [Re: Avery4] #5431382 05/17/20 12:55 PM
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eljefino Online Content
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[Linked Image from upload.wikimedia.org]

I wonder what the resonant frequency is of the tank on the handle vs on the motor. You ideally want the gas not getting vibrated and aerated.

Though the head pressure pushing down the fuel line will make it work fine by the time it gets to the motor.

Re: Lawn mower fuel tank mod [Re: mk378] #5431383 05/17/20 12:55 PM
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Avery4 Offline OP
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Originally Posted by mk378
I did something similar on mine using a 1 gallon gas can with a barbed fitting tapped into the bottom. The vinyl fuel line does look sketchy. Use rubber fuel hose instead. A shutoff near the carb is very useful.

Interesting, you must have a big yard too! The fuel line is not vinyl, it is left over PVC fuel line my motorcycle mechanic neighbor gave me. A fuel shutoff is useful, I have had to clean this mower's carb a couple times and it would be nice to not need to drain the tank if I need to service the carb again.

Re: Lawn mower fuel tank mod [Re: eljefino] #5431393 05/17/20 01:01 PM
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Avery4 Offline OP
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Originally Posted by eljefino
[Linked Image from upload.wikimedia.org]

I wonder what the resonant frequency is of the tank on the handle vs on the motor. You ideally want the gas not getting vibrated and aerated.

Though the head pressure pushing down the fuel line will make it work fine by the time it gets to the motor.

I don't know, but I can tell you that there is a lot less vibrations on the handle bars than on the motor. What I do know is that the fuel line is always full of clear fuel with no visible air bubbles. Maybe it's in my head, but I feel like the engine runs smoother with this setup. I don't know if the difference is because the carb stays full better with the extra pressure, the fuel isn't aerated if it was before, or because it stays a lot cooler.

Re: Lawn mower fuel tank mod [Re: CharlieJ] #5431427 05/17/20 01:51 PM
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Egg_Head Offline
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Originally Posted by CharlieJ
Looks like the same engine that’s on my lawn mower. (I increased the RPMs to 3600) You may have just needed a new gas cap.


How did you do that?


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Re: Lawn mower fuel tank mod [Re: Avery4] #5431440 05/17/20 02:03 PM
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Kira Offline
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An inline fuel filter would be nice.

Re: Lawn mower fuel tank mod [Re: Egg_Head] #5431441 05/17/20 02:04 PM
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Avery4 Offline OP
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Originally Posted by Egg_Head
Originally Posted by CharlieJ
Looks like the same engine that’s on my lawn mower. (I increased the RPMs to 3600) You may have just needed a new gas cap.


How did you do that?

What you do is bend the governor spring bracket back a bit to tighten the spring. The tighter the spring the higher it will rev

Re: Lawn mower fuel tank mod [Re: Kira] #5431442 05/17/20 02:05 PM
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Avery4 Offline OP
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Originally Posted by Kira
An inline fuel filter would be nice.

This tank already has a pretty fine metal screen in it over the fuel line connection to catch any large chunks, but more filtration is never a bad thing.

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