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Surging at Speed Problem

ehlien

ehlien

Regular Contributor
So I already had a problem with stalling out at idle that i have not solved yet but at least it ran good at speed. Today i went out and it ran good at speed on the way out but after sitting for a few hours when I started back it started to surge from fuel starvation at speed. The only way I could keep it from doing that was to keep pumping the fuel line bulb. It's an old fuel line and bulb but I do not see any obvious fuel leaks or cracks.The bulb does not seem to keep firm pressure and not sure if that is normal. I'm wondering if its losing vacuum. Anyway by continually pumping the bulb I was able to avoid the surging. As I pump the bulb pressure drops quickly. When I stopped pumping for a few seconds the surging returns. Anybody else experience this or have an idea what the problem might be??

Thanks much
 
Re: 1983, 50 hp 2 stroke Mariner Surging at Speed Problem

Sorry ...83 ..50 HP Mariner 4cy 2 stoke
And yes tank vent was open ....
 
The bulb does not seem to keep firm pressure and not sure if that is normal.
Click to expand...
It should only firm up when the carbs are full...then go soft but not flat.
Anyway by continually pumping the bulb I was able to avoid the surging.
Click to expand...
Check the fuel pump diaphragm and fuel lines for holes.
 
I replaced the bulb and it did not make a difference. I'm pretty sure I replaced the fuel pump diaphragms when I rebuilt the carbs last fall. I have 2 steel 5 gallon tanks. Today, with the tank I was using yesterday when this problem started, at about 1/4 full I could not get the engine to run up to speed at all. At full throttle it would hardly move and I assumed it was not getting much fuel. I switched to the second tank that was full. Right away it ran ok but after about 10 minutes it also started surging near full throttle but ran ok when I backed off to say 3/4. On the way back with about 1/2 tank left it again started surging. I had to keep pumping the bulb to make it back without surging. When i would stop pumping the bulb it would start to surge again. Now I'm wondering if there are issues with the fuel tanks?
Any thoughts out there??
 
Fastjeff asked about the tank vents...check them. If you leave the gas cap slightly loose and it runs then the vents are plugged. Does each tank have a vent?
 
It's an 83 model; did you ever check/change fuel lines? Internal degradation from ethanol fuel causes swelling and delamination. Squeezing the primer forces fuel through a damaged hose.
 
First thing I would do is replace the fuel hose from the engine to the tank. It probably needs to be replaced regardless if it's your problem or not.

If that doesn't fix the problem, check pressure from the fuel pump. If you have good pressure from the fuel pump, rebuild the carbs. Just because you rebuilt them once, doesn't mean they didn't get clogged up again from that old fuel line breaking down.

Good luck, and let us know what ends up fixing the problem!
 
some of the newer fuel tanks have a vent problem...they are trying to let air into the tank and let no gas fumes escape...try cracking the fill cap....i have one new tank that i have to run like that...i agree that if that is not the problem that the first thing i would do is change the hoses...if it hasnt been done its time anyway...and use 3/8 inch hose..not 1/4....another thing is to make sure you hose from tank does not have a dip in it....you want no gravity feed whatsoever in your gas supply...follow that rule and if the check valve is working you will not get air in the line...
 
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