Fuel feed problem?

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ktoelke54

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1998 25hp 2 stroke Mercury motor cuts out at full throttle. The cut-out happens every minute or two and lasts just a fraction of a second. It does not cut out if I drop the throttle back to 3/4. My thinking was a fuel flow issue? I’m using an old OMC 6 gal gas tank. I’m not sure if the cap on this tank needs to be loose when the motor is running? But I’ve tried it both ways and it doesn’t seem to make any difference. Also I’ve extended the fuel line to about 10’ to move the tank forward, but I’ve done this in other boats and didn’t have problems. Ive ordered new female connectors for both the motor and the tank. The connectors were old and a bit leaky so thought they might be a problem? I’m interested in feedback from anyone that has trouble-shooting experience with a similar problem, thanks.


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Rule out the connectors by replacing them,
then see if if runs properly by constantly squeezing the primer bulb.. this will tell you that the fuel pump is no good.... I'm assuming that when you went with a hose extension you replaced the entire hose.

After that I would check the float level in the carb, if that's ok i would start leaning toward an ignition issue.

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GYPSY400 said:
Rule out the connectors by replacing them,
then see if if runs properly by constantly squeezing the primer bulb.. this will tell you that the fuel pump is no good.... I'm assuming that when you went with a hose extension you replaced the entire hose.

After that I would check the float level in the carb, if that's ok i would start leaning toward an ignition issue.

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I did replace all the hose, used the old fittings though, new ones on the way. I’m hoping it’s not the ignition ( I think those cdi units are a bit pricey) but I’m a little suspicious though. It’s the way it cuts out, it doesn’t just bog down, spit and sputter, but cuts out completely then fires back up just as quick.


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CedarRiverScooter said:
Could also be a weak fuel pump. Check the simple & obvious things 1st!

Definitely going to try the bulb squeeze trick to r/o the fuel pump.


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Temporarily ‘plumb’ the fuel tank to be next to the OB motor and see if she cuts out at full throttle, if she does ... then you can’t pull that amount of fuel that far as you were.
 
I will go with Todd on this one.
Trim your engine to the lowest possible trim position and move some weight forward or take an extra passenger and seat him forward and run the boat again.
If it does not happen then move the adjustments back to original and verify the issue comes back. We can solve from there.
 
turbotodd said:
Almost sounds as if it's running up against the ignition rev limiter.

Maybe so, the motor was running at 5700 rpm according to the tach. The speed was 26, full load 14’ boat, 13 pitch prop.

The motor is new to me, either a 20 or 25hp Mercury (haven’t been able to sort that out yet, just assuming a 25). Would that make any difference as far as where the rev limiter is set? Maybe I’ll just back off the gas a tad, enough to drop a 100 rpm or so and see what happens? Wouldn’t that tell me if I’m on the rev limiter? Thanks


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Update: I replaced the female connectors on both ends of the fuel line, problem solved.


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ktoelke54 said:
Update: I replaced the female connectors on both ends of the fuel line, problem solved.


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Thanks for coming back and letting us know.

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ktoelke54 said:
Update: I replaced the female connectors on both ends of the fuel line, problem solved.


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I had the exact problem on my 86 Johnson 25hp and had the exact solution!
 

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