Leaking Carb

[JackConnick]

Arrgh.

My carb seems to be leaking gas. After servicing it now 3 times and checking the float, replacing the needle valve and seat, it's still leaking.

Frustrating, as otherwise it runs perfectly.

I replaced the scavenging tube, thinking that was the source, also the needle valve, seat and gasket. All the usual seats, etc. cleaned/replaced.

I called MM and talked to Ken, he said to double check that the float was sitting perfectly level with housing when turned over. I checked it and made sure that they seemed to be square and level.

So it seems that the only solution is a $295 new carb. (?) I leave Labor Day weekend for 2 weeks and it's too dangerous to screw around with.

But it ticks me off, as it's probably just a small adjustment somewhere.

Seems like a very poor and dangerous design, IMHO. From now on, I'm turning off and running the system out of gas. I've had a couple of scary times coming down to the boat and finding pooled gas. I service the carb about every 100 or so hours.

Jack

[Dave Neptune]

Do you have any idea where the fuel is leaking from? Unless it is the needle and seat of which you changed out something should of changed. Unless there is a crack that is about all that will leak other than a plug which is an external leak.

One possibility is a hole in a float but then the fuel will usually run out as fast as the pump pumps.

Does it leak while running?

Dave Neptune

[JackConnick]

It looks to be running out the main gasket. The floats appear to be ok, didn't have any fuel in them, checked twice.

Bone dry while it is running.

Some sort of small crack might be what's going on, but nothing visible.

Jack

[JOHN COOKSON]

Feel around the carb with dry paper towel in your hand when the carb is leaking. You might be able to tell where the leak is this way.

ex TRUE GRIT

[JackConnick]

Yeah, did that, it's on all sides slightly and leaking down. There's not a single point.

Jack

[joe_db]

The carb may have become warped. Someone on here may have a method to fix that so it seals again.
I had a troublesome carb and eventually just got a new one from Moyer and it has run perfect ever since. Also I turn my fuel pump off and run the engine out of gas when done for the day.

[Dave Neptune]

If fuel is leaking out around the main gasket then the needle & seat assembly is compromised somewhere. In order for fuel to leak out of the main gasket the fuel bowl has to be to full. In normal operation the bowl's fuel level is kept at about 1/2 bowl well below the gasket. That means that fuel is getting by when the float is holding the needle in the closed position. You also state that the carb stays dry when running.

There has to be some sort of gap either in the seat, the seats gasket or the seat itself or the needle's point has a minor flaw. Once shut off if your fuel level in the tank is higher than the carb gravity will prevail and the fuel will slowly leak by and once the engine is running the "leak" is moot as the carb uses far more than the leak can leak.

Take another close look at the needle and seat assembly with a magnifying glass of some kind.


Dave Neptune

[edwardc]

Since you've replaced the float needle & seat, I'm still suspicious of the float itself, even though you've checked it. Maybe it got bent during reassembly? A new one is only $21:

https://moyermarine.com/product/carburetor-float-fcar_02_54/

A lot cheaper than a new carb if it works! And a useful spare even if it doesn't.

A float is one of the things I keep in the "critical items I can't kludge" spares kit that I keep aboard when I'm cruising.

[dvd]

New Carb

My carb was doing the same thing. I just bought a new carb from Moyer and it’s fixed. One less thing to fiddle with. DVD

[Al Schober]

Just went through the fuel leak thing with my chipper/shredder - Tecumseh H35 was leaking fuel out of the carb. Went through it twice looking for the leak - no good. Finally held the float bowl up to the light, found two pin holes in the bottom! Looked like a snake bite - metal dented in slightly with a pin hole in the bottom of each dent. Put some epoxy on it but I don't trust it - parts on order (carb itself is no longer available).

[SubtoSail]

Based on Dave's guidance that a leak from the carb main gasket can only come from fuel leaking around the needle seat/float assembly:

Could the needle seat just not be screwed in all the way? I recently had confusion on setting the float parallel by backing out the seat.

Could the needle itself be dropped in upside down? I get turned around every time I put it back together. I'm not sure if you would be able to identify this while running, as it may function well enough when fuel is being sucked through the jets. It would then not make a good seal when shutdown and gravity could cause the bowl to fill up to the main gasket (maybe).

Of course, there could be a fracture somewhere. I think it would have to be in the bowl.

Do you have an electric or mechanical fuel pump? I'm not sure what's inside the electric pumps, but if I understand the mechanical pump correctly fuel shouldn't be able to move through it while shutdown. One of the two valves is always shut, and even if is pressure released through a leak they would both be shut by a spring.

This could also be indicative of a bigger leak in the boat fuel system. Assuming you have a shut off valve immediately downstream of the fuel tank there shouldn't be any fuel leak when shutdown. I know nothing is perfect, but like plugging the top of a straw full of liquid, even removing the carb (creating a large carb leak) should not result in the entire volume of fuel lines leaking out.

-Joe

[joe_db]

My experience is that beyond a certain point, a new carb will more than pay for itself in time spent NOT screwing with it

[romantic comedy]

take the carb drain plug out.

Find out what size pipe fits in the hole. I am guessing it is 1/8 pipe. Get a pipe nipple this size. get a clear hose the will fit over this nipple. Screw the nipple in the carb and run the engine. Hold the hose up so that it will fill to the level in the carb bowl. This will show the level and if it is too high and may be running over the top.

[JackConnick]

Thanks for all the great ideas!

Don actually called early this morning and we went over it. He seemed to be sure that it was just dirty fuel through the system.

He told me to use the electric fuel pump to flush the entire system out by jumping the oil pressure safety switch with the ignition on. I have a MM drain plug on the carb that helped, as I just had to crack open the bolt a couple of turns.

Then I just wedged a cottage cheese container with a coffee filter in it, and some pads under it, and ran the fuel pump for about 5 mins at a time to drain out about 8-10 oz of fuel. A glass container would of been nice, but wouldn't fit. A small aluminum tray might actually work well.

I attached a couple of photos. I think it's a neat trick to have in your bag...

The first time it looked like a sand bar! I did 4 drains in all following Don's directions to really flush it well. Each time it got better, finally littler or no grit was spotted.

I emptied the fuel back into the tank through couple of coffee filters and caught a ton of junk.

I drained the main fuel filter and saw just a small bit of grit, not a lot.

I decided to go ahead and change the polishing filter, even though it was only 25 hrs old. When I went to the store, they looked it up and it was a 20 micron filter, not a 10 as Don sells.

I was on a cruise in July and got a tank of gas at a small resort only open in the summer. I'm pretty sure they sold me the dirty gas.

I'll get a new 10 micron filter in the morning. Give it a test run and check later for leaks. Fingers crossed that was the issue.

Hopefully I got most of the junk out of the tank and the new finer filter will catch the rest in the future.

Jack

[joe_db]

Wow - that is a lot of sand to make it through TWO fuel filters
Note your alligator clips will spark and you are creating an explosive environment. You have to take care to do nothing that makes a spark once you are draining gas and filling the boat with fumes.

I am still puzzled by one thing - if my needle valve sticks open, I can smell gas because it pools in the carb and might even drip out around the flame arrestor connection, but the only time it ever leaked down the sides of the carb from the point the top and bottom halves connect is when the carb was warped and would not seal. I MarineTex-ed it together, which worked until I got home.