Signs of a bad fuel pump (Johnson)

rktman · Mar 23, 2016

I took my Johnson 3 cyl jet (25hp) out the other day to test a new impeller and it would not open up for the first 2-3 minutes of operation.
It idled fine but would not develop full power.
Is that common with a fuel pump going out?
Once it opened up it ran great.
It might have been water in the bottom of the tank but it was just odd that it idled so smooth.
Thanks.

GYPSY400 · Mar 23, 2016

If you pump the bulb while its running and it runs fine, then its the fuel pump ( because you are the fuel pump )

If it idles fine, but doesn't open up its either the fuel hose collapsed inside or the float adjustment on the carb too low (starving for fuel)

If it ran crappy for a bit, but now it runs fine. . Then its water in the gas

GYPSY400

rktman · Mar 23, 2016

Thanks

It ran the same while pumping the bulb. Probably water in the gas...

rktman · Mar 28, 2016

My motor did the same thing this weekend (not the fuel)
I'm thinking its running on 2 cylinders and then after warming up for 5-10 minutes, the 3rd cylinder kicks in.
I'll check the obvious (spark plugs, etc).
Would a coil pack do this?

wmk0002 · Mar 28, 2016

rktman said:
My motor did the same thing this weekend (not the fuel)
I'm thinking its running on 2 cylinders and then after warming up for 5-10 minutes, the 3rd cylinder kicks in.
I'll check the obvious (spark plugs, etc).
Would a coil pack do this?

Typically a bad ignition component like a coil or switchbox will work for the first few minutes of operation and then fail after it gets hot. But I'm sure it's possible that it warming up could have the reverse affect.

lovedr79 · Mar 29, 2016

my motor always did this when i would get it out in the spring. i discovered the float was sticking. you can try tapping on the float bowl with the handle of a screw driver. my boat would idle all day long, touch the gas and it would die. sometimes i would get just enough fule to go about 4 mph. then tap the float bowl and it would take off.

Ringo Steele · Mar 30, 2016

A little gum in the carb can also cause this effect. Mine will do that if it sits a few weeks, and then open up and run fine until it sits again for several weeks. Seafoam and fuel stabilizer helps.

Signs of a bad fuel pump (Johnson)

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