National Aeronca Association Bulletin Board

1946 7AC, with A75 engine. N7125
Slow drip, (leak), underneath carburetor whenever fuel valve is ON. Been going on for a while. Idles and flies OK. One opinion I got was, "they all leak". My first guess is float is in need of adjusting. Perhaps dirty needle valve. I will appreciate suggestions. Thanks.
Jim Heidere

No......they don't all leak. I had a Stromberg on my A65 Champ and it never leaked. Neither does the one on my 0200. I've never had to shut the fuel valve off. The needle valve should be shutting the fuel off and not letting it seep through or the float level is off or sinking. I suspect you probably need a new needle and seat. You will get some fuel that leaks back from the manifold after the engine is shut down but it should be a minimum amount and dry up fairly quickly.

I've had good luck with Bolduc in the Twin Cities with our carburetor overhauls. Not cheap but they work when you get them back.

Mike

I met an elderly gentleman at Oshkosh who specialize in rebuilding the Stromberg carbs. He told me you had to lap the needle valve and seat on a Stromberg or, odds on, it would drip. He also said to not use lapping compound. I vaguely recall asking him if toothpaste was OK. I don't remember his answer. MikeB i wonder if that was Bolduc?

Dennis

There is also a service bulletin no 73 for drilling the idle air bleed hole higher in the carb to prevent this. I lapped the new steel needle into the new seat I bought and I did the rework in this service bulletin. I have no leaks in mine. Unfortunately my a65 was on my friends Chief instead of my Champ! OH the HORROR of it all........
The carb on his A65 leaked just as you described but we have not done anything about his yet.

Oh I can send a copy of the manual to you if you would like a copy. just pm me a good email address if you can't find it.

Jim, my carb leaked too after shutdown so I always shut the fuel off everytime when done flying. I tried the lapping tricks, lapping compound and toothpaste, and it didn't work, maybe I didn't do them properly.
There is a guy in the Chicago area who rebuilds these carbs, his name is Bob Kachergius.

Often, one hears the complaint that his Stromberg carb. leaks and drips after engine shut-down. The fact is that most Strombergs DO leak and drip. The remedy is “shut the fuel selector off” and the drip stops.

This is a “Band-Aid” way of curing a leak and not really the right way to go (plus not really legal)…

Here is a real simple and quick test you can do yourself to see if the needle and seat in the carburetor are the culprits.

Remove the carburetor from the engine, turn it up side down and drain all of the fuel out of it. (Be sure you get all of it).

Next, turn the carburetor right side up, place the fuel inlet fitting up to your mouth and apply suction. Of course with the carb in the upright position, the float is at the bottom of the float bowl and the needle is wide open. You will not be able to hold suction by mouth.

Next, turn the carb. UP SIDE DOWN, and re-apply the same suction by mouth to the fuel inlet fitting again. With the carburetor up side down, the float will now have the needle in the fully seated position. After applying suction, you should be able to hold vacuum with the tip of your tongue in the opening of the fuel inlet fitting “IF THE NEEDLE & SEAT ARE WORKING PROPERLY”.

IF, you “can not” hold a steady vacuum at this point, and the fitting leaks air, the needle is definitely not seating and this is the reason your carburetor is dripping fuel.

Time to call Bob at Uni-Tech and get your carburetor overhauled properly…

This test is super simple and fast to do which makes it easy for you to make an important decision “To do---or not to do---that is the question”…

I can be reached at 708-267-7111 or emailed at uni-tech@earthlink.net to further discuss your situation.


Jim I would be interested in talking to you about your A-75 in your Champ and how you went about getting it approved and your performance numbers.
I believe you can Pm, private message me by clicking on my name and sending me a message, or here on the forum,
Jim

Jim,
These little carbs are pretty specific on float levels. You need to make sure that it's correct, but a leaky needle will cause an increase in fuel level.
One problem is that there are about three different needle styles and two different seats, some compatable and some not.
I set the float level at the aircraft it is installed on. I have a little adjustable work bench and swing the carb over to it, turn on the fuel and check the level. Then go get a few cups of coffee, smoke a lung rocket or two and check it again. Make sure it doesn't rise. Safety it all up and go fly.
Paul

I have never had much problem - some of the neoprene needles appear to not like auto fuel.

I did have one steel needle with a very rough slot. It would catch on the brass pole on the float, and cause a fuel leak. Some filing and polishing fixed that one.

Valve lapping compound is way too coarse - try polishing compound, then toothpaste.

I do Paul's test ten times. It has to stop flow at the proper level all ten times, or it is no- go.

Thanks (so far),to all of you helpful gentlemen. Very useful data.
Jim Heidere

If they're set up right they do not leak. Here is some good info on needles and seats http://thestrombergspecialist.com/index ... rb-problem and dripping http://thestrombergspecialist.com/index ... ing-letter. I went through this after mine started leaking recently (never did before). Spoke with Bob at UniTech and learned that simply rejetting for my 85 conversion wasn't technically legit (he was VERY adamant about that!). I had also moved to a field elevation of 5600' and wanted to have a mixture control. I ended up sending my carb to Aircraft Systems (http://www.acs-rfd.com/) and swapping it for the correct carb w/ mixture that they had overhauled (along with $900 plus dollars, yow!,). Engine definitely runs better since installing the new carb, and despite what many say my mixture does work!! They tore my carburetor apart to find a mismatched needle and seat. It's a wonder it went all these years without leaking sooner!

Thanks much. Bob has my carburetor as we speak.
Jim Heidere

This is a follow-up post from my previous ones regarding my leaking carburetor.
Bob Kachergius at Uni Tech Management Systems produced a beautifully overhauled carburetor for me. Installed it a month ago and several test flights have been flawless. You may reach him at 708 – 267 – 7111.

I wish I would have had this information a couple years ago when I had the carb off my Champ. Apparently, I was fed some improper information.

Larry,

Are there any airports in Sigourney? There used to be two a few years ago, but I haven't noticed any recently. I fly off my farm near Iowa City.

Jim

All the Sigourney area grass strips are back in crop now. Closest grass is Montezuma, Wellman and Blakesburg. Sully and Keosauqua aren't too far either. Couple of private ones but they don't share. With liability issues anymore I can't blame them.