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Motor Being Starved Of Fuel At Low Speeds

6/29/20 @ 11:16 AM
MEMBER since 6/22/01

For about two years now I've had an issue with my motor when I go from high speeds to back down to low speeds like when I go into a slow no wake area. The motor would either die or I needed to pump the bulb to give it more fuel.  I eliminated the possibility of it being the fuel pump because people I talked to, including a mechanic and Googling it said if it was a fuel pump issue I'd run out of fuel at high speeds as well. Anyone else have an issue like this?

TODAY @ 10:21 AM
MEMBER since 6/22/01

Yes, my new tank has that new pressure valve on it. Finally the bulb has been staying hard. I've run it for as much as 10 minutes at a time at slow no wake speeds and motor is running great. Before with the original tank I didn't lake 2 minutes at slow speeds and the bulb was soft and motor would die. It was a pain in the ass continuing to pump the bulb while moving. My problem has been I'm too cheap to take it in to have a mechanic look at it, but I think I fixed it with getting the new fuel tank, so if this permanently works then I saved myself a few hundred dollars for not having to have a mechanic look at it!

BTW, I did open the motor cover and pumped gas thru the line to check for any leaks at all before I bought the tank and I couldn't find any what so ever.

TODAY @ 8:41 AM
User since 10/7/18

My new Suzuki does it at wot but only on occasion, boat comes to a stop and pump the ball and it fires riteback up what the hell would cause that? Thinking the water seperator filter..

TODAY @ 8:24 AM
User since 1/7/02

Fishloveme, I repowered my Jon boat with a 2020 25 hp Mercury 4 stroke. It came with a fuel tank equipped with a pressure sensitive valve that will only allow 5 psi of fuel pressure to the motor. New EPA regulations require that the fuel tank can’t vent like the normal ones did. The fill cap still has a vent that you can open and it will release the pressure if it gets too great to prevent tank rupture. The tank also came with the grey gas line that is stiff as a broomstick, that gas line is considered non permeable, that is it doesn’t allow gas vapor to be emitted through the line itself. I asked about using my old, 1999 fuel tank. Dealer mechanic who walked me through the motor operation said the new motors would run poorly if at all on the older style tanks that didn’t build pressure. With your motor being a 2000 it must be a carbureted 2 stroke. I wonder how that will react with a pressurized fuel supply. 

TODAY @ 5:48 AM
MEMBER since 6/22/01

My motor is a 2000 Mercury 50 HP tiller.

So far so good after I replaced the fuel tank. I've been running the motor at slow speeds all week while fishing on my vacation. It seemed to me that the problem had gotten worse recently, to the point where I had issues even getting the bulb hard. Twice I replaced the fuel line and bulb and it seemed to help a little for a while, but this last time it didn't help at all. But replacing the gas tank has done the trick so far.

Now, question for everyone. I spent the extra money and bought a Mercury brand fuel tank. It has a special stop valve on it so that fuel won't back into the motor (or so they claim). At the dealership they claimed the ones you can get at Walmart or Fleet Farm are useless because they blow up like a balloon (I've seen this with a tank I had for my 10 horse Evinrude).  Do you think there's any truth to this about those cheap tanks not working well with these motors, or could I have probably been fine with it?

6/30/20 @ 7:48 AM
Deer Puncher
User since 1/20/17

Check the fuel line they get hard around the hose barbs and suck air

6/29/20 @ 11:02 PM
User since 12/26/10

Need more info,like year/make.Could be also those crappy fuel lines that EPA mandated.

6/29/20 @ 9:54 PM
Tim Zwieg
User since 1/10/12

Easy to check the firmness of the bulb at low speeds

6/29/20 @ 12:31 PM
Brent Hess
MEMBER since 12/18/07

I think the two most likely suspects are a small air leak in your fuel system, or a plugged low speed jet in your carburetor.

While your motor is not running, take the motor cover off, and pump the bulb until it gets really firm, then, while you’re looking at the fuel lines and carburetor, pump the bulb again, and look for any gasoline dripping from your fuel lines, or carburetor.

If your bulb stays firm, and you don’t have any leaks, your issue is very likely to be the low speed jet in your carburetor.  

You can likely fix that by running a couple of tanks of fuel, with a heavy dose of seafoam, or worst-case scenario, you may have to rebuild the carburetor.  

Those little orifices can be a real bugger to unclog. On my 15 horse Johnson, I physically pulled the carburetor out, and soaked it in a Tupperware container full of seafoam overnight, that did the trick.

Let us know how it turns out

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