Carb. leak help

KMac · Post by **KMac** » Tue Mar 14, 2006 4:49 am

I need a little help/advice. Its a long story but......

While doing an annual on my old c-170A this year I decided to have my carburator rebuilt because the accelerator pump wasn't working. It supposedly was overhauled in 1995 according to the yellow tag. Well I took it in to the only shop in the area who rebuilds Marvel Sheibler (sp?) carburators. This shop was reccomended by my mechanics and the cessna dealer. This guy has been rebuilding carbs and mags for over 50 years. Ok, nothing is as easy as it seems. The shop said my carburator was not rebuildable because it had been modified. The screws that hold the float assembly to the top half of the carb had been stripped out, filled, redrilled and retapped. The shop had an other top half of a carb that they rebuilt with the bottom half of my carb. New jets, valves etc. and a new yellow tag. I installed the "new" carb on my C-145 and ran it tested it - all working great - but - it seemed to be seeping a little around the back half of the carburator at the gasket between the top and bottom half. I left the fuel on for a day and came back to find fuel in my drip pan. Feeling that a rebuilt carb shouldn't leak (especially because my old carb didn't leak) I took the carb back to the shop. They looked at it and took it apart and couldn't find any debris in the float valve or any reason it should leak other than maybe because its a tail dragger the float was adjusted too high. They "fixed" it and I reinstalled it on the plane today. I turned the gas on and fuel was flowing out the carb like a waterfall. I had read on the forum that sometimes the fuel/float valve sticks and tapping on the carb will seat it. I tapped. The leak stopped. I flew the plane and when I got back to the fuel island and shut it off - fuel flowing out the carb again. I tapped it, it stopped. I taxied to my hanger and shut down - yep, fuel flowing all over the place again. What the heck? My plane is hangered, has no sediment in the gascolator when drained and only runs av gas. It has NEVER leaked fuel from the carb until I had it rebuilt. I know this is a long story but if any of you have had this experience or know what could be wrong please let me know. Thanks.
Kevin

Post by **Bruce Fenstermacher** » Tue Mar 14, 2006 6:04 am

Sounds like your float is hanging up and not closing the needle valve. I'd take it back to the shop ASAP.

KMac · Post by **KMac** » Tue Mar 14, 2006 4:12 pm

Thanks Bruce. Just to add a little, after I installed the carb. it leaked like I said but after I tapped on it and it stopped I ran the engine and looked for leaks before I went flying. It didn't seem to be leaking until I got back to the fuel island. My flying consisted of flying circuits around the airport -just in case I had carb. trouble. Just didn't want to give the impression I was flying with a carb. I knew might be leaking. I'll take it back again. Should it be this difficult to get it right?

Kevin

Post by **Bruce Fenstermacher** » Tue Mar 14, 2006 5:28 pm

Didn't think anything of you test flying the plane. I'd probably have done the same thing.

What I'm thinking is happening is the the float is being held down by some interference like a gasket that is getting squeezed into the way. When the float can't rise it can't close the needle in it's seat. They probably replace your needle and seat with a new one. Perhaps there is a burr catching the needle. Could be a lot of things. In either case once the bowl fills up the gas has to go somewhere and it overflows out the venturi.

When you tap on the carb the needle is seated an the leaking stops. This should not be repeatable. In other words perhaps after a rebuild where the carb is turned and tossed the needle may get momentarily stuck and the first little tap sets it free. Any sticking after that is a problem.

BTW in smaller NAS 3 carbs commonly found on 4 cylinder Continentals in Cubs and the like, it is not unusually for the needle to seep. I'm talking a drop every hour or more. In most cases the owner simply removes the head pressure by shutting off the fuel and the seeping stops. We aren't talking about the same thing here.

And to answer your question sometimes the simplest things are the hardest to fix. I would think that by this time the rebuild shop would be looking very close at your carb and not letting it out of their sight till they are sure they've fixed the problem.

KMac · Post by **KMac** » Tue Mar 14, 2006 6:04 pm

Thanks again Bruce. I'll let you know what happens.

Kevin

Jr.CubBuilder · Post by **Jr.CubBuilder** » Wed Mar 15, 2006 12:12 am

N9149A wrote:And to answer your question sometimes the simplest things are the hardest to fix.

Hey that sounds like my house plumbing, it's the simple problems that have had me crawling around under the house for the better part of two days.

I'm curious to hear what you find out about your carb KMac, hope it's an easy fix.

blueldr · Post by **blueldr** » Wed Mar 15, 2006 4:04 am

Does the shop that repaired your carburetor have a flow bench where they can hook it up to a fuel source or are they just sending it back after a dry check?

Joe Moilanen · Post by **Joe Moilanen** » Wed Mar 15, 2006 4:04 am

Hi Kmac,

If you look on your yellow tag I think you'll see that your carb rebuild date was 12-28-95. OK, how am I doing so far??? Didn't know I was a 170 pshycic did you?

I remember the day. I was doing an annual on my plane and took the carb down to Flightcraft in Portland to have an updated nozzle installed. After the one-piece venturi thing came out, some people were having rich running conditions and they offered a free updated nozzle as a cure. Mine didn't run rough but I jumped on the ban wagon and got the new one anyway. I talked Jim into taking his off and doing the same. It wasn't really a rebuild, as I remember we just dropped them off, went and had a couple of cocktails, and went back and picked them up. Sure is a small world, historical information at your fingertips...

Joe
4518C
9222A memories

KMac · Post by **KMac** » Wed Mar 15, 2006 4:49 am

Hey Joe, you're right on. It sure is cool to be in touch with someone who has some history with my 170. Being a "rookie" I thought the yellow tag indicated it was overhauled. It sounds unlikely that when they did that work in 1995 they messed the top half of the carb up if they just changed the nozzle? BL - they had a fuel source they plumbed to the carb with about a 6' gravity feed and left it over night (supposedly) with no leaks. I knew I should have been worried when the mechanic had to keep going back to his plumbing truck to get the right tools!

Actually, I did call the manager of the shop today and he was very concerned and told me to bring it back. He appologized for all the work putting it on and taking it off and ordered a new float valve for it. Thanks for all your input. I'll let you all know how it goes.
Kevin

KMac · Post by **KMac** » Sun Mar 19, 2006 7:08 pm

Carb. update.
I got the carb. back yesterday. The mechanic said he ended up taking it apart and putting it back together 4 more times. Trying to make this short - he could not get it to hold fuel under pressure. He put in new float, new float valve and finally figured that it may have something to do with the matching of the top half of the carb to the bottom half of my old carb. He put it back together with the same bottom half that matched the top, only installed one shim (washer) under the float valve and adjusted the float level and it held under 6 pounds pressure. I'll put it back on tomorrow and let you know what happens. Thanks for all your support.

Kevin