White residue in carburetor

[Golfdad75]

After three years of trouble free running today the motor would not run unless the choked. I assumed something in the carburetor, took it off and brought it home. Now I see this white powdery substance in the float bowl, any ideas.

[CajunSpike]

Generally powder in the bottom of a carb bowl means the left over fuel in the bowl dried out totally. It left behind chemicals that were in the fuel that appear as a powder.

Another side effect is that that powder can clog up the main jet in the bowl, preventing the fuel from flowing right, and causing engine running problems.

Have to remove the jets from the bowl carefully.
Clean all the small openings of the jet and the bowl itself.
Reassemble and try again.

[JOHN COOKSON]

Generally powder in the bottom of a carb bowl means the left over fuel in the bowl dried out totally. It left behind chemicals that were in the fuel that appear as a powder.
Another side effect is that that powder can clog up the main jet in the bowl, preventing the fuel from flowing right, and causing engine running problems.
Have to remove the jets from the bowl carefully.
Clean all the small openings of the jet and the bowl itself.
Reassemble and try again.

In conjunction with cleaning the the carb catch some fuel in clear glass jar and let it evaporate and see if there is indeed residues in the fuel.
Putting the cleaned carb back on the engine before you have the source of contamination known and dealt with will most likely be an exercise in futility.

TRUE GRIT

[Golfdad75]

I had a mechanic once tell me to always shut off the gas and run the carb dry. Would this solve the problem

[joe_db]

This is exactly how I have run my A4, two outboard boats, and all piston engine airplanes since forever and it seems to work well. I shut my fuel pump off when done for the day and let the engine run all the gas out. Outboards get the fuel line removed and run out and airplanes get the mixture pulled full lean and run out.
IMHO there are two sources for this dreaded white powder:
1. Something in the gas. You could evaporate some gas and see if it leaves white residue.
2. The gas is corroding the carb. I have found the long term solution to this was a new carb. Once the metal started corroding it seemed to get much more prone to it from then on. I have posted before about this issue where ethanol laced gasoline can be quite corrosive to aluminum/zinc carbs. Some fuel additives fight this and SeaFoam is the cheapest one that does a good job. Water in the fuel makes the issue much worse. I would clean the carb out, use SeaFoam, and see if it comes back. Also make SURE water isn't getting into the fuel.

[tenders]

I had a mechanic once tell me to always shut off the gas and run the carb dry. Would this solve the problem

I don't think so, except possibly at the end of the season before layup (if you live in a clime where that is necessary). Even that is going to have minimal effect.

I'm pretty sure the carb isn't even empty when the engine dies. There may still be a few teaspoons of fuel in the bottom of the float chamber that can't get sputtered up through the needle valve orifice. (My understanding is that this is the design of "updraft" carbs, which are different than the outboard carbs to which Joe_db may be referring.) The problem of contaminants left behind once that evaporates still exists. And you'd spend a lot more time hassling running the carb "dry" than you would periodically cleaning out the carb every 3-5 years as a preventative measure...or maybe never.

Installing a small "polishing filter" between the fuel pump and the carb, and run a healthy dose of StaBil in the fuel (I do that all the time), will ensure you've got the cleanest fuel in there in the first place.

[Mo]

I always put "stabil" in my gas regardless of time of year. If I purchase 5 gallons to put in the boat the stabil is added to the gas can prior to pouring it into the boat. Ethanol is not good either...here in Canada the high test gas has no ethanol, so that's what you buy if you can get it. Stabil and no ethanol, filter changes yearly. It's been a good number of years since I've had a fuel related issue.

[Golfdad75]

Gotta love the A4, took the carb off cleaned it and put it back on, runs like a champ. You don’t have to be an expert to work on these engines.