Sunken float?

N170BP · Post by **N170BP** » Thu Nov 06, 2003 8:01 pm

Folks,

My '54 drips fuel out of the bottom of the airbox right after
I shut it down. It's about a one drop per second drip, and
it drips for 20 or so seconds, than quits.

I'm thinking I either have a mis-adjusted float, or the float is
sinking (?). The carb. was overhauled with the engine around
350 hours ago during the major overhaul (in mid 2000). It has
only started dripping after sitting for a few weeks (during an
annual).

Thoughts?

Bela P. Havasreti
'54 C-170B N170BP

Post by **GAHorn** » Thu Nov 06, 2003 9:03 pm

If you're leaving the fuel valve ON, and it stops after a few minutes then it's likely just a dirty seat or mechanism or maladjusted. (If the float was fuel-soaked it wouldn't have any reason to shut off. I suspect it's improperly adjusted.) Either way, you're going to have to pull it apart to find out the reason. Check it's float-level setting.
Occasionally an owner will leave his fuel selector valve OFF and when preflighting will find fuel pouring out of the cowl after turning the selector valve ON. A "rap" on the carb bowl, or sometimes just rocking the wings will "startle" the float into operation from it's sleepy position (caused by simple dryness,....but it's healthier for the system to turn it off in my opinion.) I always turn mine off if I'm leaving the airplane unattended.

N170BP · Post by **N170BP** » Thu Nov 06, 2003 10:03 pm

Thanks George,

I initially tried gently tapping on the carb body and it did indeed
quit dripping upon doing so. Must be some junk in there like
you say. Time to find a Marvel overhaul manual for the carb.
Speaking of which, is the correct carb for the C-145-2 as mounted
in a '54 C-170B supposed to be a #10-3237 / MA-3SPA ?

One reference I found on the web says #10-3237 was superceded
by #10-4895-1 (this is from the Swift list, so I'm not sure if the same
applies to our 170s....?)

Bela P. Havasreti
'54 C-170B N170BP

Post by **GAHorn** » Thu Nov 06, 2003 10:29 pm

According to the TCM Overhaul Manual X30013 it's supposed to be a Marvel Schebler PN 10-4439 (TCM PN 628945) for all models C-145/O-300 regardless of aircraft. (Who knows what the Swift folks are doing, they're notorious for mods.) The float height (from the body split at the bowl flat) is 7/32".

N170BP · Post by **N170BP** » Thu Nov 06, 2003 10:56 pm

Thanks again George.

According to:

http://www.dgsupply.com/carbeligibility.html

the 10-4439 was also superceded by the 10-4895, which
was subsequently superceded by the 10-4895-1. I'll look
tonight to see what's bolted onto my engine (I've heard horror
stories along those lines before!). One of the C-145 powered
Swift guys found he had a C-90 carb. bolted on his engine, and
was "giving away" 10% - 20% flow/power.

I figure if I'm going to pull my carb and take it apart, I might
as well overhaul it, so I want to get the right rebuild kit.

Bela P. Havasreti
'54 C-170B N170BP

Post by **GAHorn** » Fri Nov 07, 2003 12:12 am

There are a lot of variations of the MA3 carburetor. The PN variations noted are usually the result of minor changes, but the important thing to note is that the part number you FIND may be different than that listed. You should determine that your PN either had original approval by type certificate or by other approval. (In the case of superceded PN's, you've already noted the changes are minor indeed....a simply renumbering system due to Facet purchasing Marvel. There are also -1's and -1R's, ....only notations that designate which facility rebuilt them. Depending upon which PN you search, this part can cost as much as $3800, or $970. How's THAT for sleight of hand?
The Swifts were originally typed with 85 Continentals. Some owners later installed 90's, and 125's and even 145's but saw the carb MODEL as MA3 and kept their previous carbs. Needless to say, it doesn't work that way.
I've had reports from owners that have had Precision rebuilds, and Consododated rebuilds. The best comments come from those rebuilt by Consolodated Fuel Systems. Good luck.

Tom Downey · Post by **Tom Downey** » Fri Nov 07, 2003 1:50 am

I would remove the primer line and see if that is what is leaking.

zero.one.victor · Post by **zero.one.victor** » Fri Nov 07, 2003 5:03 am

3 years ago,at major,my overhauler got me an overhauled/exchange MA-3SPA p/n 10-4895-1 carb.

Eric

Dave Clark · Post by **Dave Clark** » Fri Nov 07, 2003 2:25 pm

A number of years ago I went to sell a 180 that was running on Mogas. Parked overnight outside at the purchasers selected shop for the prebuy inspection. The inspector fired it up in the AM, taxied it to the door, shut it down and fuel ran out the airbox. This started a chain of events including pulling the carb and having a look inside all of which found no explaination. A call to a friend who had a highly respected accy overhaul shop solved the problem. He asked if I was running mogas, well yes, then proceeded to tell me it was condensing in the cold intake tubes then running down. Not usually happening on a warm engine shutdown. Also Avgas would vaporize faster with the cold intakes and never drip. Lesson learned.

N170BP · Post by **N170BP** » Fri Nov 07, 2003 4:03 pm

Thanks Eric & Dave. Couldn't make it out to the airport last night, but
I'll have a look this afternoon. I'm burning only avgas. Also, the shut-downs (where I've observed the dripping) have been after 1+ hour flights.... I'm hoping a simple cleaning of the float needle/seat assy.
and re-adjusting the float will fix the problem.

Bela P. Havasreti
'54 C-170B N170BP

zero.one.victor · Post by **zero.one.victor** » Sat Nov 08, 2003 6:32 am

A friend was having trouble with a gas drip on her C-120,and it turned out to be a bad float-needle/seat on her Stromberg carb.

Eric

scott · Post by **scott** » Sat Nov 08, 2003 12:13 pm

A stuck float will overflow the bowl till unstuck or out of fuel. This is a function of the needle seat seal. New needles have a Viton tip that helps seal. Changing the needle and seat usually solves this problem. Make sure you set the float height correctly.

I had a genuine sunk float on a MA 4-SPA. It would die on short final. I first noticed that on rollout it would die. At first I thought the idle was set too low. But I needed to crank a lot or go to ICO to get her started again.
Of course when I noticed the engine would not respond to throttle inputs on approach that got my attention.

When I took the carb apart it had a METAL float. When I shook it, you could hear just a little gas inside.
A lot of guys just bake a metal float in the oven to dry it then resolder the joints.
I got a new O/H unit from Consolidated Fuel Systems. Now my engine runs too lean. Still figuring that one out.

Dave Clark · Post by **Dave Clark** » Mon Nov 10, 2003 2:20 am

Very common problem with the Stromberg float. The book float fuel level point gets really close to where it will just leak at a three point tailwheel position so you have to sometimes set the level a little low. These are much different than our Marvelous Dribblers.

Post by **GAHorn** » Sun Nov 23, 2003 2:36 am

Dave, the earlier comment you passed along re: use of mogas and the airbox dripping fuel deserves a pat on the back. Here's a reply from John Frank, technical advisor at Cessna Pilots Assoc. to one of their members just this week:

" Gas coming from the carburetor upon shutdown is a fairly common
occurrence when operating on auto gas, especially in the fall season of
the year. It is caused by fuel vapor condensing on the intake tubes at
shutdown and running back down through the carburetor to the airbox and
out the drain.
The amount draining out can be anywhere from a teaspoon to a teacup
full. There really isn't any way to totally eliminate this condensing
of fuel, but it can be minimized by pulling on carburetor heat for 20-
30 seconds before shutting down.
This situation can occur with av-gas as well, but not to as great a
degree as with auto fuel due to the lower Reed Vapor Pressure (RVP) of
av-gas.
John Frank, CPA Tech Rep

The International Cessna 170 Association

Sunken float?

Sunken float?

Stuck float/sunk float