2009 mercury 20hp 4 stroke not running right

today while out on the river motor ran fine, was getting 20mph loaded with two people lots of gear. fished for awhile started back up river suddenly lost power. all i could get out of it was 6.5 mph. sounded like it was over loaded. cutt throttle back nothing, choked out. fuel line bulb wouldnt get tight....... took the pickup tube out of the tank, primer working properly just wont get tight. no fuel leaking out anywhere. i came home pulled plugs out they were slightly yellow. fuel filter clean, bulb tight after a squeeze or two. how do you check the fuel pump? i pulled it off but wasnt sure if it was like an old V8 fuel pump. i can blow throw it the way fuel flows, but cant blow through backwards. makes a whistling sound when you blow through it. you can also free rev with the throttle only but as soon as u put a load on it, it becomes very sluggish. not many hours on this motor either.

Check for water in the fuel.

That's on the list along with checking for air leaks at quick connects. Don't think it is as its not sputtering. How do u check the fuel pump? I have pulled it off but can't dissasemble it.

Pull the fuel line off of the carburetor and crank the engine. Should squirt fuel out. If not, either something is plugged up, there is an air leak on the suction side, or the pump is not functioning. I like to use a glass jar for fuel samples. It'll be obvious if the fuel pump is working. It'll also be obvious if there's moisture in the fuel.

Is it EFI or carb

Carb. I drained the fuel last night. No water. I did use the bulb to start the siphon, but it stopped a couple times, squeezed it and it was pushing air back into the tank, then it would also not do anything, so I believe the valve inside the bulb is the culprit. It was a new bulb the day it started acting up. I rapped it on the floor and it started functioning again...... So I will refueling with new fuel and try a new bulb. I really hope that is all it is. I was also going to hook a psi gauge on the fuel line to see how much pressure the pump is putting out. But not sure what it should he putting out. I was thinking around 6-10 psi?

Make sure your inline fuel filter is not on backwards!!!

Jeff

Lol, its not I took it out hoping it was clogged.

Make sure your bulb is not on backwards

New bulb and filter. Pray that's all it is. Don't want to buy a fuel pump.

truly irritated now. new bulb, filter, fuel line connector, ran great for about 15 minutes, then lost power again! i believe it is the fuel pump. i popped the line off yesterday and cranked it, i got fuel pulsing out. didnt seem to be under much pressure. i also realized i have warranty left, anyone ever do a warranty claim with mercury?

Must be done at authorized mercury/mercruiser repair shop

well it dawned on me I have warranty left, took it to a mercury dealer, they went through it. Ran in a tank, ran it on the water NOTHING........ So I went to their shop put the boat in ran it wide open for half an hour wide open. They claim they didn't find anything, mysteriously my motor runs smoother, starts easier and I am now getting 26 mph! Now someone explain that! The most I have ever gotten with just me in the boat was 22mph. And I got slammed with a $200 bill since they didn't find anthing........

Does the 20 HP Mercury have overheat limit? If it does...it "could" be in the pump (low volume).

I know on the smaller Yamaha's (all I've dealt with in any detail-haven't messed with Merc, Mariner, OMC much), they have overheat limit built in. If engine temp exceeds I believe 196 degrees, the CDI limits engine speed to about 2000 RPM. Just barely above an idle. Typically the complaint I get is "runs great for 10-15 minutes, then falls on it's face...shut it off, let it cool, does it all over again".

Not saying yours is "that" problem...but could be. But if it's running good now, I reckon it's good to just leave it as it is until it breaks.

Not sure if they do or not. Seems fine now. So we will see......

my 20 merc wont indle

Possible that something was clogging the fuel flow and worked its way out. Freak things do happen on ocassion !!

paul hall said:

my 20 merc wont indle

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Are you using fresh high octane fuel? Anything but HO will plug up the jets in the carb and cause an idle issue.

Stand Up said:

Are you using fresh high octane fuel? Anything but HO will plug up the jets in the carb and cause an idle issue.

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Mercury calls for 86 octane on there smaller outboards, why would that cause plugging up jets??

airshot said:

Mercury calls for 86 octane on there smaller outboards, why would that cause plugging up jets??

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Lower octane fuel has other junk in it, like corn oil so to speak that gums up after the fuel has sat for just a few days. Highest octane has way less of a chance for that. I use 92 octane.