1999 Force (Merc/Force) 75HP leaking fuel from carb vent holes & throats

dmeals

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1999 Force 75HP leaks fuel from all carbs. Fuel leaks from small vent just above fuel bowl and from the carb throats. Have removed and cleaned carbs, replaced all needles and in fact bought new bottom carb. After pressurizing bulb fuel will leak in the down or trimmed up position. Motor starts & runs great. Bringing back to slip and fuel eventually leaks from cowling all over the water. Very messy and extremely dangerous. Lots of fuel.

Again, professionally cleaned carbs, new needles (non-replaceble pressed in seats), floats properly adjusted. Checked tank vent, opened. Why do these carbs leak? Should not be allowing fuel past needle & seat! I am stumpted!! Any suggestions appreciated.
 

foodfisher

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Re: 1999 Force (Merc/Force) 75HP leaking fuel from carb vent holes & throats

If all you posted is true, the problem has to be seats, ( I believe they are replaceable, pressed in or not) or saturated floats. When inverted, did you try blowing through the carb. passage?
 

dmeals

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Re: 1999 Force (Merc/Force) 75HP leaking fuel from carb vent holes & throats

If all you posted is true, the problem has to be seats, ( I believe they are replaceable, pressed in or not) or saturated floats. When inverted, did you try blowing through the carb. passage?

According to Tolliston, non-replaceable. That is why I intially bought center carb. It is new and still leaks past seat. Have checked floats, all good with correct levels. Blowing through inverted carb, yes, needles are closing off air flow. Very strange isn't it!! Thanks for the reply.

Dan.
 

pnwboat

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Re: 1999 Force (Merc/Force) 75HP leaking fuel from carb vent holes & throats

Take a very close look at the seats. If they look OK then either the floats are adjusted too high, or there is debris getting trapped between the seat and tip of the needle valve.

I've run into situations where an there was excessive crud in a gas tank and no fuel filter installed. You could clean the carbs out all you want. Everything tested fine right after you cleaned the carbs. Take it out and the carbs leaked. More crud in the carbs.

The other scenario was due to whatever reason, the factory settings on the float adjustment would not prevent the carbs from flooding. Had to set the floats about a 32nd of an inch lower, then they worked just fine. Probably like foodfisher mentioned, floats were saturated and were not as buoyant as they were when new, or due to replacement part tolerances, factory settings had to be "tweaked".

Also make sure the "fuel enrichment" solenoid is not leaking (If you have one. I'm pretty sure you do). This replaces the butterfly choke on the earlier motors. To test, crimp off the small 1/4" supply line to the solenoid from the bowl of the top carburetor.
 

Jiggz

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Re: 1999 Force (Merc/Force) 75HP leaking fuel from carb vent holes & throats

Let me clarify one thing before chiming in. Did you say it only leaks when the engine is trimmed up all the way? or tilted all the way? The former is NOT normal but for the latter yes, it is normal for the carbs to leak fuel when tilted all the way in fact, even before reaching the full tilt position. So the secret is not to tilt all the way up unless you need to.
 

dmeals

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Re: 1999 Force (Merc/Force) 75HP leaking fuel from carb vent holes & throats

let me clarify one thing before chiming in. Did you say it only leaks when the engine is trimmed up all the way? Or tilted all the way? The former is not normal but for the latter yes, it is normal for the carbs to leak fuel when tilted all the way in fact, even before reaching the full tilt position. So the secret is not to tilt all the way up unless you need to.

carbs leak in the run position.
 

sustanetti

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Re: 1999 Force (Merc/Force) 75HP leaking fuel from carb vent holes & throats

I got the same mess going on. I'm going to rebuild fuel pump. If you figure it out, post it.
 

shurt

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Aug 27, 2007
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Re: 1999 Force (Merc/Force) 75HP leaking fuel from carb vent holes & throats

I went thru same issue with my 99 90 hp Force. Ended up taking carbs apart 3 separate times. Rebuilt fuel pump because it was a cheap possible solution and had not been done in 12 yrs. This solved my leaking fuel issues. Not sure how, but carbs don't leak no more.
 

dmeals

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Re: 1999 Force (Merc/Force) 75HP leaking fuel from carb vent holes & throats

I went thru same issue with my 99 90 hp Force. Ended up taking carbs apart 3 separate times. Rebuilt fuel pump because it was a cheap possible solution and had not been done in 12 yrs. This solved my leaking fuel issues. Not sure how, but carbs don't leak no more.

UPDATE ON THE LEAKING CARBS!

On and off several times, adjust floats, check floats, needles, seats, etc. No change. With motor in level down position carb #2 leaks in 10-15 mins from side vent hole and out throat. Felt very comfotable with carbs assembled correctly, adjusted correctly and clean. Decided to eleminate possibilities that tank, bulb, fuel pump, etc., may be cause of problem and pulled all three as an assembly. Jigged them up connected in same position they would be on motor mounted vertically on a piece of plywood and mounted in vise. Hooked up test tank with hose and primer bulb, pressurized and let sit now for 2.5 hrs. No leaks!! Re-pressurized again with bulb, no leaks!!

Forgot to mention in previous posts, after orignially cleaning carbs, adjusting, new needles, etc., test ran motor and lake tested on test tank with another fuel line and primer bulb...no leaks when returned and motor tilted up. Problem appears to have began when re-connected to boat tank and lines.

Anybody have a suggestion as to why it leaks when re-assembled on motor? This motor is on a pintoon boat, tank mounted slightly higher than motor. Tank flushed, tank vent cleaned and appears to operate correctly, lines replaced, fairly new bulb. Removed and inspected fuel pump, diaphragms ok, check valves ok.

Any ideas appreciated!!
 
Last edited:

pnwboat

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Re: 1999 Force (Merc/Force) 75HP leaking fuel from carb vent holes & throats

Only other possibility that I can think of is some debris in the fuel getting under the needle valve and seat. Make sure the small lengths of hose that inter connect between the carburetors is not starting to break down and contaminating the fuel with debris each time you hook them up. Doesn't take much. Just a small piece of crud barely visible is all it takes. Do you have an inline fuel filter between the fuel pump and carburetors? This will eliminate any debris from getting to the carbs.
 

dmeals

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Re: 1999 Force (Merc/Force) 75HP leaking fuel from carb vent holes & throats

Only other possibility that I can think of is some debris in the fuel getting under the needle valve and seat. Make sure the small lengths of hose that inter connect between the carburetors is not starting to break down and contaminating the fuel with debris each time you hook them up. Doesn't take much. Just a small piece of crud barely visible is all it takes. Do you have an inline fuel filter between the fuel pump and carburetors? This will eliminate any debris from getting to the carbs.

I run a boat shop and we see the delamination of the non-ethanol lines all the time...agreed! Thanks. We have replaced all fuel lines with EPA Compliant/Ethanol Resistant Line. Yes, new filter just before the fuel pump. Have flushed tank as well, fresh fuel. This one is strange no doubt!!!!!
 

pnwboat

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Re: 1999 Force (Merc/Force) 75HP leaking fuel from carb vent holes & throats

The in-line fuel filter should be placed just "after" the fuel pump. Between the fuel pump and carburetors. That way, even if the any of the rubber components in the fuel pump start to deteriorate, the filter will take care of it.
 
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