Carb Drip

[Richard Boyer]

Ok, I'm getting Carb drip out of the carb air(?) tube. Also the carb seems to be wet with fuel. So....the T is grounded till we figure it out. My IA says it could be a stuck float.

One thing I'm doing differently is using more Auto gas. I'm sure this is unrelated (or maybe it isn't) but we just replaced the fuel shutoff valve with a Cub one from WagAero. The one on my plane looked nothing like what you guys have described in the past.

Richard Boyer
N95791

[Jim Herpst]

Re: Carb Drip

Richard, If you are using more mo gas lately... what is the needle valve in the carb?. If it is not stainless steel then that perhaps is the problem. There is much discussion on the use of neoprene tips on the needle valve... will not drip(less likely) when shut down but will cause big problems if used with mo gas. I would suggest removal and tear down given your circumstance....

Best of luck....
Jim

[mulwyk]

Re: Carb Drip

Does the carb drip with the fuel valve off?

Bob Gustafson

[alwaysoar]

Re: Carb Drip

Or, Assuming you have a Stromberg NA-S3A1, you can get a drip when the plane is parked tail low because the fuel level in the idle tube rises above the idle air bleed hole. The fuel drains from the tank throught the carb onto the ground. A new hole can be drilled higher up, and the old hole plugged. If that has already been done, a 1" yellow dot is painted on the side of the carb. Other possibilities are as already mentioned, sticking float, worn float fulcrum pin, improper installed float needle, improper float level, or wrong needle for fuel used.

One way to check to see if it's leaking out the idle bleed hole is to put the tail on a saw horse in a level position and see if it still leaks. Unless it's pouring out, a drip is not necessarily a big deal. When you shut it down, shut it down with the fuel shut off. If it operates ok, then you may be ok.

p.s. mine leaks on the ground but runs fine. I just turn the fuel off when it's parked.
Ed@BTV VT
TF 527

[mulwyk]

Re: Carb Drip

My carb overhaul guy put it this way: "There's two kinds of needle valves for the Stromberg. (1) the steel needle that works just fine on car gas, but doesn't seal that good, so it usually drips and (2) the plastic tip, or rubber tip needle that doesn't drip unless you use car gas. The car gas eats away at the plastic tip and then it leaks too. So either way, shut off the fuel valve when you stop the engine."

Bob Gustafson

[Dick Smith]

Re: Carb Drip

This makes interesting reading re: the needle discussion:

http://www.bowersflybaby.com/tech/stromberg%20needles1.pdf

Dick

[Forrest Barber]

Re: Carb Drip

I have not shut off my fuel valve except to check that it works about every 40 hrs.... SS needle is the only way. Have an old tractor mechanic stake it in for you and then set her up for a couple of days with 19" head pressure, that is a tube into a funnel set 19" above the float level

[N96337]

Re: Carb Drip

Quit burning car gas Richard.
John H.

[peerlesscowboy]

Re: Carb Drip

I think those ol' Stromberg carburators all drip a little when the a/c is parked, anyway mine does, always has & I've always run Avgas. I just leave a drip pan under it parked in the hanger. Drip is slow enuf so the pan evaporates faster than the drip, leaves a residue of red dye (now turning to blue) in the bottem of the pan. If you're parked tied outside on the ramp continuously it'd prob'ly be best to shut off the fuel valve.

John C. Saubak

[selje]

Re: Carb Drip

I had my carb overhauled and now have no problem with a leak. Use mainly auto gas.

[Robert Lees]

Re: Carb Drip

Mine leaks all the while...so I turn the fuel off (mostly on the ground, of course, but occasionally in the air to see if the student is paying attention).

[Jim Hartley]

Re: Carb Drip

No drip and I do a 75% car gas and 25% 100LL.

Jim

[paulnuss]

Re: Carb Drip

For those who "blame" auto gas for a leaking carb, assuming you don't have a neoprene-tip needle valve that has deteriorated due to chemical reaction with fuel or fuel additives, what specific chemical or mechanical quality do you ascribe to automobile gasoline that it would leak out of a carburetor and aviation gasoline would not?

I will state strongly that your low-compression Continental A-65, A-75, C-85 will run better and longer on unleaded 87-octane auto fuel than it will on 100LL aviation fuel, because of lead in the Avgas. The carburetor drip is usually due to the difficulty of lapping the float needle valve to the seat perfectly enough to hold without leaking over long periods of time. Or, wear, or misalignment, or dirt, or scratches on the seating surfaces from foreign debris.

In the small Continental engines, the relatively low compression ratios and resultant maximum flame temperatures, even at the highest power outputs, will not permit these little engines to scavenge the lead from the combustion chamber. Low power settings and rich mixtures add to the problems. The lead will precipitate out of the burnt mixture, onto internal combustion chamber areas, coating cylinder heads, piston tops, valve stems and spark plugs with lead deposits. In other higher-compression engines with higher flame temperatures in the combustion chamber, the lead remains in suspension and is expelled out the exhaust without precipitating out. The most common early symptoms of the problem are fouled spark plugs; sometimes when you remove them you'll find thick deposits of lead surrounding the plug electrode recess, building up thickly until the electrode gap is bridged completely and the plug won't fire. Meanwhile, thick lead deposits build up on valve stems, and another common problem is sticking valves. A teardown will often show lead deposits in ring grooves, hampering the rings' normal movement and impairing their sealing function.

There are some issues that complicate things a little. The valve seats and faces of the older engines require some coating thickness of lead to assist in resisting wear. And there may be alcohol and other additives that make for a variance in the auto fuels we purchase. I use auto fuel routinely, although I usually try to blend with some 100LL avgas for some lead. 100LL typically specifies 2 ml of tetraethyl lead per gallon; the old 80-octane avgas had 1/2 ml/gallon; unleaded autofuel has 0 ml/gallon. Therefore a blend of 25% 100LL with 75% auto fuel will approximate the tetraethyl lead content of the old 80 octane avgas not usually available any longer, and which mostly avoided the lead buildup problems. This blend has worked fine for me for the last 25 years and several thousands of hours operation in various aircraft with older engines.

[Richard Boyer]

Re: Carb Drip

My carb hasn't leaked in 5 years, and I have used car gas off and on. In the past couple of weeks, I have seen the fuel over the bottom of the carb and out of the carb heat down tube.

What I failed to mention is that after a shutdown, it is a real pain in the keester to get it started again (warm). And I have a starter! The last time it would start but would die almost immediately if I pushed in the throttle. I am guessing that it was really flooded.

The last time I shut it down, I pulled the fuel shutoff and waited until the engine quit.

I am going to take the carb apart and check out the needle valve. (at some point....)

Richard Boyer

[dewhitaker]

Re: Carb Drip

Hi Richard, just a thought, try checking your primer, make sure it is not leaking through. That can cause the symptoms of dying out when you advance the throttle.