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PostPosted: 18 Oct 2016, 20:00 

Joined: 31 Aug 2015, 02:36
Posts: 42
Location: North Carolina
i hadn't ran my boat in about 2 months. i took it out the other night and it was really slow to accelerate and also didn't want to plane. once i got to top speed the boat still felt slow. after running it down the river for a few minutes it started bumping or jolting. the motor would have these small spikes where it would rev up. it did that all night. i don't think its bad fuel. i use 10% ethanol but i add marine sta-bil and it normally runs fine like that. i do think its a fuel issue maybe a fuel line or connectors. the jolting reminds me of the jolting you get when you run out of gas. Am i way off or does it sound like i should replace my fuel line?


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PostPosted: 21 Oct 2016, 08:30 
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Joined: 02 Mar 2014, 19:52
Posts: 3193
Location: Central FLORIDA - The Sunshine State -
Quote:
i do think its a fuel issue maybe a fuel line or connectors?


- yes -
start from the tank and double check the clamps and fittings.
the squeeze bulb is often the culprit if it is old, hard and brittle.

Remove the hose end fitting at the motor and pump the gas
by hand into a clear plastic bottle ...... This will give you an idea of any restrictions.
if WATER and other crap goes into the bottle, time to clean the gas tank.
remove the carb bowl to check for water or gunk.
This is when a good quality clear inline fuel filter is beneficial.
check the O-rings in the quick disconnects.... if they are chipped, cut, cracked or bad,
air can be sucked in at this connection - resulting in less than favorable fuel delivery.

also, do you have the little vent screw on the gas cap ??? this must be
loose/open when running the motor.
when was the last time you had the fuel pump apart ??
it may have some issues: hard/brittle/cracked diaphragm, clogged filter screen,
sucking air through the gaskets, etc.
if you have the standard issue gray fuel line, there are reported problems
of the inside liner coming "unlaminated" causing a portion of the
plastic liner to interfere with the fuel flow. To check this, remove the clamps
and fittings - cut the hose back a couple of inches, reassemble with new hose clamps.

a couple of good videos on the old YouTube: (there are many).
https://youtu.be/8GJxpXfakP4
https://www.youtube.com/watch?v=PglRQK0at1o


check all that when you can - report back with your findings.
if I missed anything, there are many very talented and experienced motorheads here to help you.



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PostPosted: 13 Feb 2017, 23:21 

Joined: 12 Feb 2017, 21:19
Posts: 72
Location: Winfield Mo
Johnny is right, a fuel filter is a must a small piece of junk the size of a grain of sand will stop your carbs from working properly.


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PostPosted: 14 Feb 2017, 01:22 
Donor
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Joined: 15 May 2010, 00:38
Posts: 2621
Location: Central Florida
A quick way to check to see if it a carb issue (restriction) is to bump the primer at the RPM where the issue is occurring. The engine should pick up every time you bump it if that is the issue. Just a bump...do not hold it in long.
Then....go check the other stuff if you want.


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PostPosted: 15 Feb 2017, 17:33 
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Joined: 05 Feb 2016, 03:42
Posts: 399
Location: Langley, BC
Had this exact issue on my Mercury 40hp jet. It was a torn fuel pump diaphragm.


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PostPosted: 15 Feb 2017, 17:53 

Joined: 28 Sep 2014, 09:02
Posts: 255
Location: Charlottesville, VA
stinkfoot wrote:
Had this exact issue on my Mercury 40hp jet. It was a torn fuel pump diaphragm.


Yup certainly could be the issue.

Maybe try having someone pump the bulb up while running and see if it fixes the bogging issue.

Those carb rebuild kits are only $12, and a kid on ice cream cones and now and laters could rebuild it in a half hour.


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PostPosted: 19 Feb 2017, 01:00 
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Joined: 15 May 2010, 00:38
Posts: 2621
Location: Central Florida
Hint.....if you have a torn diaphragm in the fuel pump it will be a constant issue, not intermittent.
Second,if you pump the bulb and have a torn diaphragm it will flood the engine immediately.
To check for a torn diaphragm is easy. Few ways to do it. Pinch off the fuel supply line and in a few seconds the engine will clear up and run. Any longer and you will deplete the fuel in the fuel bowl. Pull the pump of the side of the engine and pump the bulb. If the diaphragm is torn it will spray fuel at the pulse line opening where it connects to the block. If it is a three line pump you need to disconnect the air line to do this. Doubt this is your issue but check if you want to.


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