Gas Pouring from exhaust

[UberGoober]

Picked up a 1448 alweld with a 1997 3cyl 40hp Yamaha. Motor came from family member who let it sit for a while but said it had low hours and ran fine when parked. It cranks and idles fine but very sluggish rev. I noticed it's dumping gas from exhaust. The carbs were severely gummed up and I'm assuming the float/s were sticking. After cleaning the carbs thoroughly, replacing plugs, and cleaning fuel lines/filter, I was convinced it would fix the issue but no change. It'll plane off and run ~ 18mph but that's it. Took it about 1 mile down the river and back and it used every bit of 2 gallons of fuel. Also, I checked compression today, and it's running 120,105,105 psi which kinda concerns me, that's a 12.5% difference. Any suggestions?

[panasonic]

Picked up a 1448 alweld with a 1997 3cyl 40hp Yamaha. Motor came from family member who let it sit for a while but said it had low hours and ran fine when parked. It cranks and idles fine but very sluggish rev. I noticed it's dumping gas from exhaust. The carbs were severely gummed up and I'm assuming the float/s were sticking. After cleaning the carbs thoroughly, replacing plugs, and cleaning fuel lines/filter, I was convinced it would fix the issue but no change. It'll plane off and run ~ 18mph but that's it. Took it about 1 mile down the river and back and it used every bit of 2 gallons of fuel. Also, I checked compression today, and it's running 120,105,105 psi which kinda concerns me, that's a 12.5% difference. Any suggestions?

My guess is you still have trouble with all or one of your carbs. Sounds like it one of your floats is sticking and that carb is pouring fuel through that cylinder big time. It must be only running on two cylinders, thus the low speed. What are the plugs looking like?
I don't think the difference in compression between cylinders is your trouble and you may find that after you get the engine working right they will be much closer to each other.

[Sequoiha]

Sounds like the block mounted fuel pump might have a busted diaphragm . Leaking fuel into the cylinder.

[UberGoober]

Thanks for advice fellas. Ima pull the carbs again and check the floats again, everyone here at home has suggested the same.

Sequoiha, I never suspected the fuel pump being the issue. Can you elaborate on that? How would a broken diaphragm continuously dump fuel and wouldn't the floats have to be stuck open for it to dump the excess fuel into the cylinder? Excuse my lack of knowledge, this is my first marine motor.

As far as compression, after reading more I realized it should be done with a warmed motor and open throttle. Am I right? I'll probably start there again.

[DennisG01]

You are correct with the thought on compression testing. It can provide more accurate results that way. But regardless, those first numbers you posted are really nothing to worry about. The compression is definitely NOT your problem - that's a good thing! In other words, don't go chasing a problem that doesn't exist. Stick on the fuel path of "problem finding".

Does this engine use a portable gas tank? Although this wouldn't explain the fuel dumping issue, if you're pulling fuel off a built-in tank then the fuel would be old and it loses it's "energy" as it gets old. I would "assume" if you're using a portable tank that there would be fresh fuel in there.

I have never really messed with cleaning carbs, but just from what I've read on here, I often see mention of making sure to be able to physically see through the jets.

[UberGoober]

Thanks for the reply. Yeah I realize those compression numbers are within spec, just concerned with the difference between cylinder 1(120) and 2,3 (105). I guess that was a tangent and should've been a topic of it's on.

It is a portable tank. At first I cleaned the one it came with and refilled it. Then I used the one from my dads new boat just to make sure. Both jets in each carb were clogged, but I pulled them and cleaned them until light was visible and carb cleaner could pass through. I think it's getting plenty of fuel, way too much in fact, hence the fuel pouring from exhaust.

[DennisG01]

So it's not uncommon to see the compression numbers "normalize" once cylinders/pistons/rings are warmed up. And you may or may not still see a difference once you do it again. All I would say on this is to just write things down and monitor it over time. Even if the numbers don't come closer together, I wouldn't really worry about it - it may just be a "it is what it is" thing.

I agree - fuel supply doesn't explain the extra fuel out of the exhaust. I only meant to try and help eliminate variables as there's always a possibility that there's more than one thing going on here. That said, there's some extremely knowledgeable people on this forum that can help much more than I can with this issue. The less "variables" they have to work with, the better they can help you.

How do the spark plugs look from each cylinder?

[rodbolt17]

sounds like a busted fuel pump or a needle leaking.
I usually wont do carbs without replacing the pump.

[99yam40]

fuel pump is operated by the pulse from #3 crankcase.
If that diaphragm gets a hole or tear it will suck fuel into #3.
unbolt it without taking the lines off of it, pump the primer bulb, and see if fuel comes out of the pulse port on the pump.

also If you take the plastic silencer off of the front of carbs you will be able to see if there is raw fuel being dumped thru any of the carbs when you pump the primer up good and tight or when running

[TownsendsFJR1300]

Sounds like the block mounted fuel pump might have a busted diaphragm . Leaking fuel into the cylinder.

+1 ^^..

If the carb float was stuck open, fuel would also come out from the carb throat (visible end of the carb).

I'd check that (as noted above) before yanking any carbs..

Fuel is being dumped into the crankcase, thus, the visible fuel and with the higher RPM's, its sucking MORE FUEL into the crankcase..

[UberGoober]

Thanks for the replies guys. I've been at work and haven't had a chance to check it out, but this fuel pump diaphragm is starting to give me a glimpse of hope. Will report back with findings.

[99yam40]

do not forget to look into the carb throats , before ripping them off again

[TownsendsFJR1300]

Thanks for the replies guys. I've been at work and haven't had a chance to check it out, but this fuel pump diaphragm is starting to give me a glimpse of hope. Will report back with findings.

And fortunately, it's a pretty cheap/easy to test and replace the diaphragm...

[UberGoober]

Well, unbolted the fuel pump from block and pumped the bulb, and its gushing fuel from the hole that leads to the block. Guessing the diaphragm is indeed busted. Pulled the silencer and No fuel coming out of throats. Also pulled the bottom plug wire while running and no change in idle.

As far as the compression, I warmed it and opened the throttle and got 110psi on all three cylinders.

Thanks for the info guys. Never would've discovered the diaphragm. Didn't realize fuel pump was ran on pulse.

[TownsendsFJR1300]

Well, unbolted the fuel pump from block and pumped the bulb, and its gushing fuel from the hole that leads to the block. Guessing the diaphragm is indeed busted. Pulled the silencer and No fuel coming out of throats. Also pulled the bottom plug wire while running and no change in idle.

As far as the compression, I warmed it and opened the throttle and got 110psi on all three cylinders.

Thanks for the info guys. Never would've discovered the diaphragm. Didn't realize fuel pump was ran on pulse.

That plug is likely fouled from the excess fuel..

I'd replace all 3 plugs (cheap enough) when you do the diaphragm..

Sounds like the carbs are fine..

The fuel likely evaporated out but you may want to spin it over with the plugs out (safety cord pulled to kill the ignition) just to make sure... You don't want to foul another plug.

Plz post back once it's going again!