Carb Overflows

[Al Schober]

This has been the season of the overflowing carb. Sometimes it does, sometimes it doesn't. Seems to have become an issue ever since my electric fuel pump died. Have cleaned the float needle and seat numerous times, and replaced them once. It's gotten to the point that when I leave the boat, I have to shut off the fuel at the tank. Yesterday things seemed fine. Engine running nicely on the new electronic pump, no sign of overflow. Left the tank valve on. Came down today and the boat smells like a gas tank, and the bottom of the carb is wet with gas.
I've checked the floats. Weighed them on a gram scale, put them in the sun for an hour, no change in weight. Adequate test?
I've checked the float chamber for leaks with water. Filled and placed on paper towel - dry after 30 min.
Thought of excess tank pressure due to blocked vent. Removed the fill cap with no sign of pressure being relieved.
I've got a 15psi pressure gauge on order & will install Tuesday evening. This will give me some more info.
So folks, what am I missing? Float valve seems like such a simple thing. If mine is working, logic says the carb shouldn't overflow.

[Mo]

Al, do you have a polishing filter. Just thinking maybe some dirt is getting by and interfering with the needle seat.

[Al Schober]

Mo,
I've got both a Racor main filter before the pump and a polishing filter after the pump. The Racor is the smaller filter (not the one Don sells) - installed that last year. Not sure of the micron rating of the polishing filter - just an aluminum can filter from NAPA for 5/16 hose. I don't think I can do more with the filtration.

[Antibes]

Did you measure the float once installed? They need to be bent to have a 9/64 gap between float and body.

Also is the tip still on the float needle?

[Al Schober]

I have not measured the height of the floats above the upper body. I'll have to put that on my list of things to do. Height looked good by eye, but I did bend the arm to give a little more height. This is NOT a run lean or run rich issue - engine seems to run fine (adjustable main jet, which I haven't touched this season).
Float needle and tip look (and are) new.

[JOHN COOKSON]

Is the tank higher than the carb? If so you might have a siphon going that is overpowering the needle valve sometimes.
Maybe the old fuel pump blocked the siphon and the new fuel pump is letting the siphon happen?

TRUE GRIT

[Al Schober]

Hi John,
That syphon idea crossed my mind, which is why I'm anxious to see the results with the pressure gauge.
What do you think about the idea of adding a solenoid valve to the inlet of the Racor? It would open only when there's voltage to the fuel pump.

[JOHN COOKSON]

Hi John,
What do you think about the idea of adding a solenoid valve to the inlet of the Racor? It would open only when there's voltage to the fuel pump.

Sounds good 2 me. I've also heard of check valves at the top of the tank outlet tube but don't know how well they work.

TRUE GRIT

[ndutton]

My 2¢

I'm a big fan of a positive shut off valve (mine is immediately ahead of the carb and easily accessible) but for a siphon to exist the float valve must be open and siphon related pressure at the carb is far less than normal pump pressure. Something is amiss with your float valve and while the additional shut off is good for safety, it's looking a bit like a work-around for the real problem.

[Mo]

Mo,
I've got both a Racor main filter before the pump and a polishing filter after the pump. The Racor is the smaller filter (not the one Don sells) - installed that last year. Not sure of the micron rating of the polishing filter - just an aluminum can filter from NAPA for 5/16 hose. I don't think I can do more with the filtration.

Should be fine...that's pretty much what I use.

[Al Schober]

Neil,
I agree that the float valve should shut things off - it always has.
Once I get the pressure gauge, I intend to water test the float system and see if I can tell what's amiss. Bad gasket on the float valve seat? Crack in the casting? I don't really want to do that kind of investigation with gasoline!!
I found what seems to be a suitable solenoid valve on eBay for $13 - 12V, 1/4" NPT. I'll just add it to my Racor inlet with a pipe nipple and wire it in parallel with the fuel pump. That should prevent the slow transfer of my fuel from the tank to the bilge.

[JOHN COOKSON]

Just A thought

What float drop measurment have you been using?
Maybe the floats aren't floating high enough to ram the needle valve fully into the seat for a complete seal.

TRUE GRIT

[BunnyPlanet169]

I found what seems to be a suitable solenoid valve on eBay for $13 - 12V, 1/4" NPT.

UL listed for marine inboard gasoline use? That would require a manual override, and it passes the 2.5 minute flame test. Just curiously cautious....

[Al Schober]

John,
The main jet seems to be at or above the level of the bowl. To overflow through the main jet, the floats would have to be completely submerged! I will check 'the Book' and set float heights correctly. But unless the floats are flooded (which they don't seem to be), I don't think that's the issue.
BP,
No, no nothing on the valve - just 12V on, 0V off. I checked a few of the valves offered and nothing seemed to say USCG or marine - perhaps I should have looked further. But for $13, a first try. Do you have a particular valve in mind? Right now I'm just trying to get rid of the gas dripping off the bottom of the carb (which I'm sure isn't USCG approved).
New pressure gauge came today - cute little thing. 1.7" diameter, 1/8" NPT out the back, 0-15psi - carb will get a short nipple to the side of an 1/8" tee, top of the tee will get the gauge, bottom of the tee will get a straight 5/16" barb. At least I'll know what the pump is putting out.

[BunnyPlanet169]

Al- Don't get me wrong - I'm hardly the poster boy for regulation, but with gas I'm a lot more cautious about engineering.... if it doesn't say UL or USCG approved, it probably isn't. I guess I'm wondering why you're not using a 1/4 turn manual shut off? No wiring. I have one at the inlet to my Racor, and it's off when I leave the boat.