Honda 2HP fuel tank


Bob Larkin
 

I was just doing routine maintenance on my BF2D Honda (16-years old).  I noticed that the forward side of the fuel tank was "sucked in" around a half inch.  This was early this morning and it was around 70F, and not hot, so when I opened the cap, it popped out a little bit.  I put a big screw driver in the tank and could push most of it back to be rounded out, instead of pushed in.

It sure looks like it is going in and out, like a bladder would, with changes in temperature.

Do they all do that?  Has anybody else seen that?  I'm not sure I ever looked for it before!  Bob


Jove Lachman-Curl
 

I've had this happen with plastic gas cans in my garage, if they sit for a few months mostly empty they suck in and create a vacuum.
My first thought is that the fuel is oxidizing and consuming the oxygen to create a vacuum.... We've all done the water into a glass with a match trick right?
My second thought is that it's breathing from hot to cool and creating a vacuum like a canning jar does when it cools....... heats up, forces out the gasoline vapour, cools and creates a vacuum. The cap acts like a one way flap valve.
Solutions could be leaving the tank full during storage. OR leaving the cap cracked open a little.
Maybe someone knows which answer is correct.
-Jove

On Tue, Jul 12, 2022 at 11:02 AM Bob Larkin <bob@...> wrote:
I was just doing routine maintenance on my BF2D Honda (16-years old).  I noticed that the forward side of the fuel tank was "sucked in" around a half inch.  This was early this morning and it was around 70F, and not hot, so when I opened the cap, it popped out a little bit.  I put a big screw driver in the tank and could push most of it back to be rounded out, instead of pushed in.

It sure looks like it is going in and out, like a bladder would, with changes in temperature.

Do they all do that?  Has anybody else seen that?  I'm not sure I ever looked for it before!  Bob


Case Turner
 

The off road fuel cells that I use for extended travel are plastic. The manufacturer of those recommends burping them several times a day when fuel is in them. They also recommended storing them empty, caps loosened or off for long term storage. 

Case

Sent from not here

On Jul 12, 2022, at 11:30 AM, Jove Lachman-Curl <jovelc87@...> wrote:


I've had this happen with plastic gas cans in my garage, if they sit for a few months mostly empty they suck in and create a vacuum.
My first thought is that the fuel is oxidizing and consuming the oxygen to create a vacuum.... We've all done the water into a glass with a match trick right?
My second thought is that it's breathing from hot to cool and creating a vacuum like a canning jar does when it cools....... heats up, forces out the gasoline vapour, cools and creates a vacuum. The cap acts like a one way flap valve.
Solutions could be leaving the tank full during storage. OR leaving the cap cracked open a little.
Maybe someone knows which answer is correct.
-Jove

On Tue, Jul 12, 2022 at 11:02 AM Bob Larkin <bob@...> wrote:
I was just doing routine maintenance on my BF2D Honda (16-years old).  I noticed that the forward side of the fuel tank was "sucked in" around a half inch.  This was early this morning and it was around 70F, and not hot, so when I opened the cap, it popped out a little bit.  I put a big screw driver in the tank and could push most of it back to be rounded out, instead of pushed in.

It sure looks like it is going in and out, like a bladder would, with changes in temperature.

Do they all do that?  Has anybody else seen that?  I'm not sure I ever looked for it before!  Bob


--
Dirt


Bob Larkin
 

Interesting stuff in the Honda Service Manual for the 2 HP.   According to the "Fuel Tank Inspection Procedure," you should "Check the outer fuel tank surface.  Replace the tank if a red layer or an off-white layer appears at the surface."  The picture points to that area that flexes with heat and cool.  This is all visible by taking the cover off.  I read this as, the tank is intended to flex, but too many flexes can be bad.  Mine shows no red or off-white.  Whew!!


Electri-Cal
 

Thanks Bob, a good thing to watch for.  I noticed a 2 gal. can flex while in my Dock box at home. It was new, so maybe new ones need to age at first ??  Then the plastic ages slowly till replacement time, sure don't want scaling plastic in the fuel, eh ??  One web mechanic Mentioned ethanol in gas causing plastics to shed hydrocarbons or other bad stuff with age.  He has replaced or rebuilt many carbs with ethanol damage,  We all know this by now, but maybe tanks should be replaced after years of service.  I threw out 5 six gallon tanks a while back, no visable damage, but who knows.

In changing from built in to a new 3 gallon tank and hose under the seat, I notice relaxing a few mm's instead of swelling, but the new tanks have the vent built into the tanks cap, no more ruined fuel pump diaphragms.  It feels loose even fully tight, probably a one way valve as I've seen no leaks of spray.

Later, ----  Cal