engine cuts in and out

rnyer

Cadet
Joined
Nov 7, 2003
Messages
9
70 hp 2002 Johnson 4 stroke (J70PL4SN) will run fine for awhile and then starts to slow and then picks up again. Doesn't do it all the time. Have replaced fuel line and fittings from tank to motor. Didn't help. Any ideas of what to check next? I live in upstate NY and would like to have motor ready by spring. (Which up here is may-june!)
 

ezeke

Supreme Mariner
Joined
Sep 19, 2003
Messages
12,532
Re: engine cuts in and out

Surging is frequently caused by air leaks in the fuel system. Put a little steady pressure on the primer bulb and inspect for fuel leaks; if fuel can get out, air can and will get in.
 

PhilfromOhio

Petty Officer 3rd Class
Joined
Feb 7, 2010
Messages
82
Re: engine cuts in and out

Do you have a service manual? I know this may and probably isnt the problem, however I read in one of my old manuals than engine cut outs can also be related to worn drive gears. just a thought, however water in the fuel, or a cracked line is most likely the cause... good luck.
 

tashasdaddy

Honorary Moderator Emeritus
Joined
Nov 11, 2005
Messages
51,019
Re: engine cuts in and out

does you fuel line primer bulb go flat?
 

teded72

Recruit
Joined
Jan 18, 2010
Messages
4
Re: engine cuts in and out

Mine did that for a while. The ball valve in the primer bulb broke and the ball would get sucked up against the fuel line. Took me a few frustrating trips to the lake to figure it out! Check the fuel pump?
 

ezeke

Supreme Mariner
Joined
Sep 19, 2003
Messages
12,532
Re: engine cuts in and out

When the primer bulb collapses, the problem is the bulb or between the bulb and the gasoline unless the tank vent is clogged.

Check the fuel pickup screen in the tank and the anti-siphon valve. The anti-siphon valve is generally inside the outgoing fuel line connection at the top of the built-in tanks.

Most anti-siphon valves consist of a spring loaded steel ball; they are easily clogged. Some older ones don't function well with ethanol.

If you have a water-separating fuel filter, you may need to check that as well.
 
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