# Johnson 70 surging at wot



## Mack17 (Sep 8, 2013)

Hey guys just thought I'd ask if anyone experienced their motor surging at wot.I have a 1980 Johnson 70 and when I first got the boat and ran it the first time it was surging right around 3/4-full throttle.So I found out that the fuel hose had a liner inside that was collapsing.So replaced it and still had same results.Next the check valve in primer bulb was sticking and allowed fuel to back flow to tank so replaced that as well.Next did the fuel filter and quick connects.Also cleaned out tank and pickup tube and gave it fresh fuel it's a vented tank as well.The next time I took boat out it ran perfect we ran about 15miles that day without a hickup.Anyways the boat sat for the last 3 weeks with stabil treatment added.Well took boat out today and after about two hours with no issue it started surging at full wot.3/4 throttle it ran fine I checked tank vent and it was open and had fuel in filter so was holding prime.I had my buddy pump the bulb and it seemed to help but not really.Motor also has new plugs so not really sure why it's starting again.I'm thinking I either need to clean carbs or have a vaccuum leak or a fuel pump going bad.Any of yall ever have this issue ? I appreciate any help at all.Thanks,Ron


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## earl60446 (Sep 9, 2013)

Gonna keep an eye on this one, my 48hp johnson started surging at WOT too end of last season. I have changed fuel, plugs but no help.
Tim


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## PSG-1 (Sep 9, 2013)

Sounds to me like a fuel pump issue. Also, check your anti-siphon valve between the engine and fuel tank (if so equipped) These 2 things can cause erratic performance, particularly surging at high speed.


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## Clam (Sep 9, 2013)

Was the tank full of fuel when it was running good? I had a 48 SPL run good with a full tank but surged when the fuel got to a certain level in the tank. After throwing numerous parts at it I finally replaced the fuel tank and it cured my issue. I would top off the fuel tank again and run it to see what happens. If it continues to surge start squeezing the primer ball at wot to see if that cures it, if so your fuel pump may be bad.


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## Pappy (Sep 10, 2013)

From the statement he is claiming using the primer bulb had an effect but not really............okay?....................
Would definitely go through the carbs as the surge may be indicative of a lean condition/surge which can severely damage the engine. If you are competent at this and do it properly it will eliminate that as a cause.


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## Mack17 (Sep 10, 2013)

Appreciate the help guys.Yea the tank was pretty much full when it started surging. I thought I fixed it when I replaced the line,filter and quick connects.And the last time I had it out it ran fine all day so who knows.I'm going to replace the fuel pump and go thru each carb and check all fuel lines and for vaccuum leaks.It may be sucking air somewhere.Boat is out of commission for right now as I am recarpeting the deck and going to repaint the hull,motor and trailer.Also have to fix the power tilt/trim and swivel bracket so I have plenty of time to go thru everything properly.


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## Mack17 (Sep 12, 2013)

Well I think I may have found the issue.I pulled the motor cap off and pulled the fuel pump cap off that houses the inlet screen and noticed the lines that were running from the pump to carb is that old grey attwood fuel line.As soon as I saw it I had a good idea what the issue was I pulled off the inlet line going to fuel pump and looked into the inlet tube on cap and pulled out a 1/2" piece of rolled up liner :shock: .I was holding it in my hand trying to figure out how my motor even ran lol.So I then turned it over and removed the screen and there was more ! I cleaned it out so I may have fixed the reason why it was surging [-o< .I'm going to pull all them grey lines and replace with the blue fuel line.Won't know exactly if that was the problem until I get lines replaced but I'll post back when I do.If yall have them grey lines change them out and check you fuel pump inlet and cap screen for pieces of liner.


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