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Author Topic:   Carburetor Engine: Fuel Leak From Carburetor
quayman posted 06-19-2005 03:29 PM ET (US)   Profile for quayman   Send Email to quayman  
Today I squeezed the [primer] bulb and started my two-stroke, 225-hp outboard. I let it run only a moment, then killed engine. A minute or two later I raised the trim way up to check prop. Gas leaked out of the engine into the transom.

Is this normal with a full carb or does it sound as if there's a gasline leak or something?

I am taking the boat to a mechanic tomorrow to check-out, but was onboard just for a minute today and this happened. Expert opinion welcome. I don't want to trailer to the shop if it might blow up. Thank you.

JOHN W MAYO posted 06-19-2005 03:51 PM ET (US)     Profile for JOHN W MAYO  Send Email to JOHN W MAYO     
I had a Merc 150 hp carb 1500.
Mine would have and did do the same as yours.
If you do not raise the motor all the way up where the engine is tilted in the transom area you do not have this problem of leaking fuel do you?, if not I suspect it is probably just the fuel draining out of the carbs when tilted about 45 degrees.

You could run it again, with the cowling off and turn it off, tilt the motor and I suspect you would see it.

jimh posted 06-19-2005 04:53 PM ET (US)     Profile for jimh  Send Email to jimh     
Outboard motors that have carburetors also have float bowls in which a local reservoir of fuel is maintained for each carburetor. On a 235-HP motor you probably have six carburetors. If the engine is running and the fuel system is operating properly, the float bowls of all the carburetors will be full of gasoline.

If you tilt the engine to an extremely high angle, it is very possible that the fuel in the carburetor float bowls can escape.

If you have gasoline leaking into the transom splash well when the engine is tilted up to maximum, it is most likely coming from the carburetors. Of course, you cannot confirm this without checking for a leak, but this is a rather common occurrence on engines with carburetors.

It is also possible that there is a bad float valve in a carburetor and fuel was overflowing the float reservoir.

Gasoline evaporates rather rapidly, so the spilled gasoline should dissipate quickly. Of course, gasoline vapor is highly explosive if in the proper concentration, but a small amount of spilled gasoline in an open air environment is not going to explode spontaneously.

quayman posted 06-19-2005 05:32 PM ET (US)     Profile for quayman  Send Email to quayman     
Jim ... You are a great editor and, seemingly, an even better engine expert and, I suspect, a welcome source of knowledge in many other areas for all in these forums.

Thanks also to you, John.

As must be evident from my Continuous Wave posts in recent days, I recently acquired a Whaler Outrage with 225 hp outboard and am troubleshooting before heading for the horizon.

When all is shipshape, will submit photos for posting.

Again, thank you.

Don88outrage posted 06-20-2005 08:53 AM ET (US)     Profile for Don88outrage  Send Email to Don88outrage     
Had a similar problem on a carburated 150 Johnson, there's a possibility that fuel may be collecting in the lower engine compartment with the engine in the down position and and then draining into the well when tilted up. It took me quite a while to find that one fuel line that had a crack in it, with 3 carbs on a 150 it's near impossible to inspect all the fuel lines with the carbs installed. Ended up removing the carbs to inspect all the lines and thats when the cracked line was found. At the same time after going through that much effort installing carb kits, needle, seats, floats, etc. is a good idea.
quayman posted 06-20-2005 09:33 AM ET (US)     Profile for quayman  Send Email to quayman     
Thank you for your replies.

Two people responding to similar post on message boats say to have engine inspected ASAP, that gas leak such as this is NOT normal under any circumstances.

We'll see.

Again, thank you.

jimh posted 06-24-2005 12:31 AM ET (US)     Profile for jimh  Send Email to jimh     
I disagree--with a carburetor the fuel system is open to the air and if the carburetors are oriented in the right position they will leak fuel. The degree to which this happens depends on the particular engine, the carburetors, and the orientation. My 1976 Mercury did this all the time if tilted all the way up.

Fuel should not leak during normal operation. A small amount of fuel spilled when an engine is tilted to the full up position is fairly normal for certain engines. Usually it is caught under the cowling and diverted down the engine leg so it is not noticed.

jimh posted 06-24-2005 01:29 AM ET (US)     Profile for jimh  Send Email to jimh     
quayman posted 06-24-2005 06:58 PM ET (US)     Profile for quayman  Send Email to quayman     
Some forum readers may see the posting I made recently on Continuous Wave noting that my 225 hp outboard had stalled at idle and then wouldn't start.

Also, that when trimming the motor to look at the prop that a little gas fell out of the engine into the boat's transom well.

I was worried, but problem solved:

Mechanic says one of the engine carbs was missing a screw and the engine was running on five cylinders. With engine trimmed up, gas in the "loose" carb leaked.

The missing screw had probably shaken loose over time, he said.

Thanks for your postings. See you in the forum.

jimh posted 06-24-2005 09:54 PM ET (US)     Profile for jimh  Send Email to jimh     
Thanks for the the follow up. Good info!

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