Engine Sputter is back

[Kma4444]

Sounds like vapor lock to me. Getting more and more common. Fuel used to be formulated to resist that as cars with fuel pumps that pulled fuel from the tank, around hot things, over hot asphalt, would boil the fuel and not be able to pump the vapors. Runs the float bowls low an fuel and you get the lean condition you describe. Today's cars, with pumps in the tank and high pressure fuel systems will not suffer that malady. It's frustrating that we are having to relearn how to cure vapor lock as it had become almost extinct. The new alcohol fortified fuels are even more prone to boiling under heat and vacuum.

You need a pump as close to the tank as you can get it. If it's vapor lock you will fix it. Just buy a cheap electric pump and wire it through the ignition switch. An extra plus is, it makes starting after sitting long enough to evaporate the fuel out of the carb really quick. When you turn on the ignition, it fills the float bowls. No having to crank and crank to get the mechanical pump primed and fuel up to the carb.

[SquamInboards]

Do you have a check valve inline on your vent hose? The length shouldn't really matter, so long as it's able to pull air through.

I really think running the boat on an external tank the next time you have the issue would go a long way toward diagnosing the problem, or at least pointing you in the right direction (supply-side or delivery-side).

I agree that probably opening your gas cap was the thing that made the difference that time, not the additive. I suppose you could also try just opening the cap next time it happens.

[wotan2525]

Is there a loop or slack in your vent anywhere? Running it all the way to the front of the boat makes me think there is a low spot that could pool gas and not allow it to vent properly.

[trayson]

Do you have a check valve inline on your vent hose? The length shouldn't really matter, so long as it's able to pull air through.

I really think running the boat on an external tank the next time you have the issue would go a long way toward diagnosing the problem, or at least pointing you in the right direction (supply-side or delivery-side).

I agree that probably opening your gas cap was the thing that made the difference that time, not the additive. I suppose you could also try just opening the cap next time it happens.

No check valve

So what are you thinking? Disconnect the fuel line that goes out of the fuel filter from the fuel pump and put that into a gas can?

Is there a loop or slack in your vent anywhere? Running it all the way to the front of the boat makes me think there is a low spot that could pool gas and not allow it to vent properly.

There is some slack in the vent line. It's a run that goes from the gas tank up to by the windshield so it's be hard to get a perfect slope on it...

[trayson]

Sounds like vapor lock to me. Getting more and more common. Fuel used to be formulated to resist that as cars with fuel pumps that pulled fuel from the tank, around hot things, over hot asphalt, would boil the fuel and not be able to pump the vapors. Runs the float bowls low an fuel and you get the lean condition you describe. Today's cars, with pumps in the tank and high pressure fuel systems will not suffer that malady. It's frustrating that we are having to relearn how to cure vapor lock as it had become almost extinct. The new alcohol fortified fuels are even more prone to boiling under heat and vacuum.

You need a pump as close to the tank as you can get it. If it's vapor lock you will fix it. Just buy a cheap electric pump and wire it through the ignition switch. An extra plus is, it makes starting after sitting long enough to evaporate the fuel out of the carb really quick. When you turn on the ignition, it fills the float bowls. No having to crank and crank to get the mechanical pump primed and fuel up to the carb.

I bought a cheap electric pump for $40 that I've been using to drain the gas tank (when I had to remove the tank to install my transom lights and also my Surf system). Is that all I'd need? I'd just put it inline then near the tank and wire the positive to the ignition circuit. seems easy enough.

[whammond]

So what are you thinking? Disconnect the fuel line that goes out of the fuel filter from the fuel pump and put that into a gas can?

Yep, you want a line straight from the external gas can into the mechanical fuel pump. That existing line from the fuel filter housing to the fuel pump is pretty short, but it may be long enough.

You may have to get some extra fuel line anyways to do this test. I'd just go ahead and replace your fuel lines. It really isn't that difficult, just a little annoying because mine had all these plastic clips w/ screws that held the fuel line close to the side of the bilge. Assuming you haven't replaced them since you got the boat, i'd just do it and have peace of mind and be done with your lines.

Now i'm going to start spitballing: Concerning the potential vapor lock issue, (essentially your gasoline boiling somewhere along the way, typically inside the fuel pump). What degree thermostat are you running, 143 or 160? And following that, what's your typ. operating temperature? I have the 143 in mine. You could always try running your engine cooler, and see if that helps the issue. Having tried both degree thermostats (and one time putting a thermostat in upside down), the engine temp is obviously related to the temp inside the dog house. If you keep the engine cooler, the fuel pump, etc. stays cooler. As a test, you could just take the thermostat out and run it around for a while and see if the problems resurface. I wouldn't suggest doing this all the time as your engine isn't meant to continue running that cold.

It also could just be the fact that your fuel pump is beginning to give way and just isn't creating the amount of pressure required at higher rpms. I replaced mine, and I took apart my old one and the seals and gaskets on it were in bad shape. I'm guessing from gas w/ ethanol in it. You could always pull your fuel pump and open it up and see what it looks like.

Diagnose and replace the cheap things first....rinse and repeat.

[SquamInboards]

So what are you thinking? Disconnect the fuel line that goes out of the fuel filter from the fuel pump and put that into a gas can?

If you have any friends with small 4-stroke outboards you could ask to borrow their fuel tank (assuming it's removable). Then you could probably use the line right from that tank, take off the outboard connector and put the hose right onto the fuel pump and hose clamp it for your testing purposes. It is a little depressing to see how fast an outboard tank gets drained by one of these engines, actually.

As you have been wisely trying to eliminate things without throwing expensive parts at it, this is a good way to narrow down your focus. I wouldn't touch the distributor until I was certain the problem would occur with the boat running on a completely different fuel source. Same goes for the fuel pump, and for the added electric fuel pump. There are a lot of good ideas being suggested here, I'm just suggesting a way to narrow down which one might be right.

[trayson]

Yep, you want a line straight from the external gas can into the mechanical fuel pump. That existing line from the fuel filter housing to the fuel pump is pretty short, but it may be long enough.

You may have to get some extra fuel line anyways to do this test. I'd just go ahead and replace your fuel lines. It really isn't that difficult, just a little annoying because mine had all these plastic clips w/ screws that held the fuel line close to the side of the bilge. Assuming you haven't replaced them since you got the boat, i'd just do it and have peace of mind and be done with your lines.

Now i'm going to start spitballing: Concerning the potential vapor lock issue, (essentially your gasoline boiling somewhere along the way, typically inside the fuel pump). What degree thermostat are you running, 143 or 160? And following that, what's your typ. operating temperature? I have the 143 in mine. You could always try running your engine cooler, and see if that helps the issue. Having tried both degree thermostats (and one time putting a thermostat in upside down), the engine temp is obviously related to the temp inside the dog house. If you keep the engine cooler, the fuel pump, etc. stays cooler. As a test, you could just take the thermostat out and run it around for a while and see if the problems resurface. I wouldn't suggest doing this all the time as your engine isn't meant to continue running that cold.

It also could just be the fact that your fuel pump is beginning to give way and just isn't creating the amount of pressure required at higher rpms. I replaced mine, and I took apart my old one and the seals and gaskets on it were in bad shape. I'm guessing from gas w/ ethanol in it. You could always pull your fuel pump and open it up and see what it looks like.

Diagnose and replace the cheap things first....rinse and repeat.

Undoubtedly original fuel lines.

That said, my engine rarely seems to run hot. Not that I'm really that good about mentally logging what the temps are. But I know that whenever I look, I think it's below the halfway mark on the temp gauge.

I'm thinking that the fact it ran well after opening the gas cap might be of interest...

[SquamInboards]

I'm thinking that the fact it ran well after opening the gas cap might be of interest...

... yeah that. I forgot to add: since you "solved" the issue last time when you opened the gas cap, try that next time it happens. Just a quick open, close, and fire it back up. To the lake! More research required...

[trayson]

... yeah that. I forgot to add: since you "solved" the issue last time when you opened the gas cap, try that next time it happens. Just a quick open, close, and fire it back up. To the lake! More research required...

Without a doubt I'm going to see if that makes it better. if so, that's certainly worth pursuing. I probably won't be on my boat until the weekend though. yesterday was on someone else's v-drive and tonight is the same, someone else's boat. Tues - Thurs is supposed to rain. So we'll see what happens when I get back on my boat.