So my Marvel Schebler is drooling gas, everywhere. My A&P and I took it off today and his recommendation was swap it out for an overhauled one. This seems like a logical plan but I would love to hear of past experiences, thoughts, or ideas. O-470-r with an MA-4-5 carb.
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I’m a big fan of the carb shop at Lycon. They’ve done many carbs for me and there’s one of theirs on my airplane.

Carbs and mags are super important, don’t screw around, get it overhauled.

I used http://www.aircraftcarbs.com/ in Justin, TX for the same carburetor, 2 IA’s on my field recommended him and use him frequently. Very quick turn around and 30 years of AD compliance were caught up with, for under $1000 I believe. Call and talk to the guy if you use him first, he’s an old man running a one man show, he’ll shoot you straight on what to expect.

Where is it coming out of? The nozzle? Could be as simple as a float problem. If 8ts not an upgraded float it might be leaking and just sinks which causes them to leak.

Its leaking where the air box bolts to bottom of the carb

Mantoga wrote:Its leaking where the air box bolts to bottom of the carb

That just means it's coming from the carb throat, likely. Your A&P should have been able to discern something more detailed than that when he removed the carb and airbox?

Zzz wrote:

Mantoga wrote:Its leaking where the air box bolts to bottom of the carb

That just means it's coming from the carb throat, likely. Your A&P should have been able to discern something more detailed than that when he removed the carb and airbox?

I agree with Zane. I'd almost bet it is a float issue.

I have had a couple MA4-5 carbs apart, they are very simple and parts are readily available but for the cost of a rebuild kit you might as well send it out, the difference is only about $200 between doing it yourself and getting an exchange unit already done. If I can fix it with float/gaskets/jets I’ll do it myself but if it needs new bushings/throttle shaft or machine work I just exchange it for an overhauled carb. I have gotten the best prices from Airmark in Ft Lauterdale, they just send the carbs to Marvel Schebler but for whatever reason it’s a bit less expensive than sending them to MS directly.

Update, while cowl was off to replace alternator my mechanic noticed fuel leaking out between the bottom of the carb and top of air box, the place where the carb heat door lives. He recommendation was to replace carb with new one. Today we installed new carb, unfortunately had to reuse old paper gadget that goes between bottom of carb and top of air box. We ran up the motor with. The cowling off, and once again when we shut off the engine about a tablespoon of fuel leaked out between the bottom of the carb and the top of the airbox. This is getting really really frustrating, I have a new gasket now for that mating but that just means once I shut off the motor some gas comes down the carb and sits in the air bowl where the carb heat door resides. On all engine runs the engine ran flawlessly. Any thoughts or suggestions would be greatly appreciated, were stumped. Plane type is 66 182J with O-470-r and marvel Schebler ma-4-5

That gasket between the air box and the bottom of the carb isn’t to keep fuel from leaking, it’s an air seal only.

That leak you’re getting might be from the mixture being rigged wrong, are you shutting the engine down with the mag switch or mixture cutoff?

I’m shutting it down with the mixture cutoff

Since you replaced the carb, I would also check the O-rings in the primer and make sure the primer is locked closed too. You may be sucking in fuel through the primer while running. Then when you shut down it could be draining back down the intake tubes and out through the carb into the airbox.

I'm not sure you have a problem. The 0-470 induction is such that all the fuel is not burned and upon shut down the fuel collects on the induction tubes and runs back and drips out as you mentioned, more noticeable when cooler. If you only get a tablespoon and it stops this is what I would suspect. Since it runs good I probably wouldn't be concerned. If you are still concerned you can run it without the air box and have a mirror ready to look up carb throat. Might want to consider opening throttle wide open when you pull the mixture if you are going to do this test. As you are aware the fuel from the accelerator pump would need to be considered. I would probably do 2 runs and have throttle open on one and closed on the other.

bush master wrote:Might want to consider opening throttle wide open when you pull the mixture if you are going to do this test. As you are aware the fuel from the accelerator pump would need to be considered. I would probably do 2 runs and have throttle open on one and closed on the other.

This makes a lot of sense, I’ve noticed similar results with an R985. I’ll usually run at 1000 rpm for 90 seconds at shutdown to evacuate oil, but if I forget or am in a rush and kill it after idling, it tends to drool a little avgas after shutting down.

Shutdown at 1000 not idle. Makes for less vacuum downstream of the throttle plate to suck fuel from the carb. The carbs don't always seal perfectly inside and high vacuum can pull fuel. Disconnect primer fuel feed and cap off that line. See if the drool quits as primers can leak with bad seals. As noted not all fuel gets vaporized at low rpm/closed throttle so some may drip back at shutdown. Make sure the mixture cutoff is fully closed at shutdown. But again it's not a perfect seal or the parts wouldn't rotate to adjust the fuel flow. And accelerator pump discharge check valves can leak. A good repair shop can test or replace those parts.

All noted in above comments. That's why we put "NO SMOKING" placards on the panel.

Gary

I've had a leaky float valve on my MS on my 182...could smell it as soon as I entered the hangar after leaving the fuel system on. I replaced the seal, which fixed it, but it came back a while later. I cleared the screen and flushed the system, returning the fuel through a chamois. It never came back. The leakage didn't happen at all if I shut the fuel sector off while taxiing prior to shutdown, which was the clue.

On a different plane, I replaced the throttle shaft o rings to fix very minor leakage after shut down. The problem wasn't the leakage..it was the weird mixture behavior when running. I don't think you'd ever get enough leakage to add up what you are seeing though.

I don't think a leaky primer (mentioned previously) would be the issue, but it takes just a few minutes to replace the orings with quality fuel proof ones from the local parts store. I've watched some heroic efforts chasing down a bad loping idle cutoff problem when the only thing wrong was a shredded $0.20 O ring in the primer. Bit again, I'd be surprised if it had anything at all to do with your problem.

If a fuel supply fitting is cracked, it might also be drooling. Hard to imagine that going unnoticed on the replacement though.

Are you using car gas?
John

Yes, I was, I’ve had two different mechanics say that autogas could be the culprit. So I’m switching over to avgas. We rebuilt primer last summer and even disconnected it to be sure, plus checked for intake leaks and even did a compression check