Evaporation from fuel tank

[Thirtyaughtsix]

So it turns out my gas tank is evaporating no less than a half gallon of premium here in the summer if I let the bike sit for a full day and that's my very generous guess, I honestly think it's closer to a full gallon. Ran out of gas riding around the other day and had to throw the petcocks on reserve to get home, much to my surprise as I though I had 5 gallons remaining, was luckily not even a mile from home. Gas tank is an 850T original, other than my paint job and mgcycle gas cap that's maybe a year old.

Obvious question is, what can I do to prevent this?

[Aaron D.]

Please take this in the spirit offered.
No way in hell is your tank losing that much in evaporation in a day. Check your oil level to see if it has risen, and find the leaky petcock.

[yogidozer]

What Aaron said...or, maybe you were riding further than you thought you were? 

[Tom H]

Please take this in the spirit offered.
No way in hell is your tank losing that much in evaporation in a day. Check your oil level to see if it has risen, and find the leaky petcock.

Had that happen to my Eldo. I was on a trip and stopped for lunch and left the petcock open. Then probably went about 100 miles. Decided to check my oil and it came pouring out the dip stick hole. Probably had the cleanest engine out there! I did do an oil change at the first parts store I found.

Tom

[Wayne Orwig]

Agreed.
If the petcock was on, or leaking, a leaking float was pouring gasoline past the rings into the oil. Sniff the oil. That will damge the rings quick too.

[Huzo]

Is there no overflow on the bowls anymore as in days of yore ?

[Tom H]

If the bike in question has the VHB carbs. There is an overflow hole. But it it's not leaking badly, the gas can slowly flow into the cylinder through an open intake valve and make it way into the crankcase.

Tom

[Thirtyaughtsix]

If the bike in question has the VHB carbs. There is an overflow hole. But it it's not leaking badly, the gas can slowly flow into the cylinder through an open intake valve and make it way into the crankcase.

Tom

You talking about that hole about halfway down then? Both sides are like this, lower half covered in a film of fuel. You may have to forgive my ignorance here, but I had always thought this was just a thing that was natural for all old carburetors to do lol

[yogidozer]

so, was their fuel in the oil?

[Thirtyaughtsix]

so, was their fuel in the oil?

Not that I could tell, no. She's due for a change and was a little below the 2nd line, no gas that my nose could detect

[Chuck in Indiana]

Agreed.
If the petcock was on, or leaking, a leaking float was pouring gasoline past the rings into the oil. Sniff the oil. That will damge the rings quick too.

And the main and rod bearings. Don't ask me how I know..

[RinkRat II]

       

Obvious question is, what can I do to prevent this?

    Double check that your cap has some type of pressure/vacuum relief valve . Most newer caps have vacuum and  pressure relief valves built in to prevent evaporation but still allow fuel to flow to the carbs.  Your system may be old enough when they didn't have this feature and there is little you can do to stop it.
   If it's any consolation, this time of year in Arizona  My Sport evaps out about a half gallon over a weeks period of time.  Gas ain't what she used to be!

          Paul B

[redrider90]

It is highly unlikely that it is leaking past the carb into the crankcase. The OP said he may loose as much as a gallon a day and yet the engine runs. I think an extra gallon of fluid to the crankcase would cause the engine to hydraulic and end of story.
I had that happed to a 13 HP B&S lawn mower engine. One day I go out to mow the law and got about 30 feet and it threw a rod broke a hole in motor.
I said what just happened here. I'm thinking no oil and I pulled the dipstick and it was full to the top. I smelled it and it was gas. I open the gas tank and it was empty. My float had stuck over the previous week or so since last cut. It made quite a racket when it blew while I was sitting on it. 

[yogidozer]

sure your wife isn't draining it so you'll mow the lawn? 

[Triple Jim]

Great song, Yogi!

[Thirtyaughtsix]

sure your wife isn't draining it so you'll mow the lawn? 

Positive, we rent currently so neither of us have to mow lol

[Thirtyaughtsix]

Think I found my problem lol, to think it's gone 700ish miles like this. I say this as I took it to a shop to tune it for me cause I had known the bike had always ran rich in my time with it and could never get to the bottom of it, I guess the shop couldn't either

[yogidozer]

plug on the left looks like there is no gap? could be the angle

[Thirtyaughtsix]

plug on the left looks like there is no gap? could be the angle

It's the angle I promise, it threw me for a sec too before I snapped the pic

[pehayes]

Think I found my problem lol, to think it's gone 700ish miles like this.

When people write about spark plug issues I always refer to this:

http://www.guzzipower.com/Sparkplug-pehayes.html

My Guzzis have always been happy.
EF, SPII, Convert, Eldorado, V50, V65

Patrick Hayes
Fremont CA

[Huzo]

Think I found my problem lol, to think it's gone 700ish miles like this. I say this as I took it to a shop to tune it for me cause I had known the bike had always ran rich in my time with it and could never get to the bottom of it, I guess the shop couldn't either

Are they both the same reach ?

[Thirtyaughtsix]

Are they both the same reach ?

How far off from each other would they have to be for it to concern me?

[RinkRat II]

 
  Depending on what plug is called for for your bike,  that is the plug you need to use. If one of your plugs is 3/4 reach and the other is 5/8 that is unacceptable. Plugs are designed to allow the tip or electrode to just sit inside the chamber to ignite the fuel, if it doesn't and sits up inside the threaded portion it won't ignite the fuel properly. Conversley if it's too long it may damage the piston should it hit the plug.

       Paul B

[rodekyll]

RR is pranking you.  AOf course they do.  The ngk part number tells you the thread diameter, Length, heat range, tip type, resistance, etc.  There is nothing random about them.  All B6ES are identical.

[Thirtyaughtsix]

  Depending on what plug is called for for your bike,  that is the plug you need to use. If one of your plugs is 3/4 reach and the other is 5/8 that is unacceptable. Plugs are designed to allow the tip or electrode to just sit inside the chamber to ignite the fuel, if it doesn't and sits up inside the threaded portion it won't ignite the fuel properly. Conversley if it's too long it may damage the piston should it hit the plug.

       Paul B

Oh no it's nothing like that, they're both the same plug out of the same box. Like I'm sure they're not perfectly equal as I had to gap them but I'd think only a pair of calipers would be able to tell

[RinkRat II]

   Good to know, a few thousands here and there won't matter but if someone had installed the wrong plug that would be trouble.

       Paul B