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1999 Mercury/Force 75HP leaking fuel from carb vent holes & throats

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dmeals

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1999 Mercury/Force 75HP leaks fuel from all carbs.Fuel leaks from small vent just above fuel bowl and from the carb throats. Haveremoved and cleaned carbs, replaced all needles and in fact bought new bottomcarb. After pressurizing bulb fuel will leak in the down or trimmed upposition. Motor starts & runs great. Bringing back to slip and fueleventually leaks from cowling all over the water. Very messy and extremelydangerous. Lots of fuel.

Again, professionally cleaned carbs, new needles (non-replaceble pressed inseats), floats properly adjusted. Checked tank vent, opened. Why do these carbsleak? Should not be allowing fuel past needle & seat! I am stumpted!! Anysuggestions appreciated.
 
In general these carbs do leak (old Tillotson's), but yours sounds to be leaking excessively.

They will leak when tilted up (or in the "trailer" position if you like) but should not leak with the motor in the normal running position and not if you pump up the primer bulb with the motor down in the normal position.

Can only assume that your "properly adjusted" floats are not "properly adjusted" - I would bend the tabs a little on each float until you no longer get a leak by pumping the bulb in the running position. These are crappy old carbs, but they shouldn't constantly flood on you...
 
galamb said:
in general these carbs do leak (old tillotson's), but yours sounds to be leaking excessively.

They will leak when tilted up (or in the "trailer" position if you like) but should not leak with the motor in the normal running position and not if you pump up the primer bulb with the motor down in the normal position.
leaks with motor down in "normal" position

can only assume that your "properly adjusted" floats are not "properly adjusted" - i would bend the tabs a little on each float until you no longer get a leak by pumping the bulb in the running position. These are crappy old carbs, but they shouldn't constantly flood on you...
Click to expand...
floats are adjusted correctly
 
Since the motor is not in front of me I can only tell what would cause the leak.

If the floats are adjusted correctly then the gas has to be getting by the needle valves or their seats - there just isn't any other way the fuel could get from the bowl up to the throats after pumping up the bulb on the fuel line.

And as I stated, and I have seen quite a few Force motors over the years, they are a little leaky, but not to the extent you make it sound - and definitely should not leak, in the normal running position, simply by pumping up the fuel line.

If that's the case then there is an issue with the float, needle or seat, whether or not the were professionally serviced...
 
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galamb said:
Since the motor is not in front of me I can only tell what would cause the leak.

If the floats are adjusted correctly then the gas has to be getting by the needle valves or their seats - there just isn't any other way the fuel could get from the bowl up to the throats after pumping up the bulb on the fuel line.

And as I stated, and I have seen quite a few Force motors over the years, they are a little leaky, but not to the extent you make it sound - and definitely should not leak, in the normal running position, simply by pumping up the fuel line.

If that's the case then there is an issue with the float, needle or seat, whether or not the were professionally serviced...
Click to expand...

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!!
 
When the carbs were mounted on that board (I use a vise to adjust each carb separately), you didn't have any leaks. However, the bulb you were using apparently did not make as much pressure as the one in the boat. You need to redue that test, using the pump from the boat and REALLY pump them up. If--when--they leak, drop the float level 1/16 " at a time until it stops.

Jeff
 
fastjeff said:
When the carbs were mounted on that board (I use a vise to adjust each carb separately), you didn't have any leaks. However, the bulb you were using apparently did not make as much pressure as the one in the boat. You need to redue that test, using the pump from the boat and REALLY pump them up. If--when--they leak, drop the float level 1/16 " at a time until it stops.

Jeff
Click to expand...

Thanks for the response Jeff. Why would I drop the float level? Dropping the float would cause the needle to shut the fuel supply off later than sooner...right??
 
Then you'll need another needle and seat. Just because they're new doesn't mean they are okay.

I've had to go back to used ones to get 'em to seal! Ditto for check valves in a fuel pump.

Jeff
 
dmeals said:
1999 Mercury/Force 75HP leaks fuel from all carbs.Fuel leaks from small vent just above fuel bowl and from the carb throats. Haveremoved and cleaned carbs, replaced all needles and in fact bought new bottomcarb. After pressurizing bulb fuel will leak in the down or trimmed upposition. Motor starts & runs great. Bringing back to slip and fueleventually leaks from cowling all over the water. Very messy and extremelydangerous. Lots of fuel.

Again, professionally cleaned carbs, new needles (non-replaceble pressed inseats), floats properly adjusted. Checked tank vent, opened. Why do these carbsleak? Should not be allowing fuel past needle & seat! I am stumpted!! Anysuggestions appreciated.
Click to expand...




I have the same problem with my 1998 120 hp merc Force engine fuel leaking from the bottom carb bowl vent. Ive cleaned both carbs, Ive changed the fuel pump, Ive removed the reed valves and checked for daylight, OK, checked the coils for a miss using a timing light on each coil I had someone else drive while I checked. Ive switched the bottom and top carb and the problem still remained at the bottom location. Ive also rebent the carb floats and yet nothing. It idles fine, 1/4 throttle fine, 1/2 and 3/4 when the rpm's get around 3900 and up the bottom carb starts leaking. and when I pump the squeeze bulb when not running they both overflow. just thought some of my ideas might help you diagnose your problem. If you have any luck figuring it out I would like to know as well.
 
Wow; that's really weird.

Glad I didn't use those carbs for my project motor!

Jeff

PS: Are you sure the fuel pump diaphragm isn't leaking gas into the motor from a pin hole?
 
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