loss of power , running rough '99 Suzuki/Evinrude 40hp 4 stroke

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MadTom

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Aug 23, 2011
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Was cruising at 4700 rpm when I noticed a quick loss of rpm and power. I slowed throttle down to a slow cruise to make it home and although the motor appeared to be running rough, I made it home. Restarted and problem stayed. Installed new plugs, add fuel stabilizer(sea foam) in the case it was water in the fuel(same brand same station I use Shell V-power). Went out for a test drive - seemed smooth running at 4700 rpm for a few minutes until I throttled down to retrieve a cushion that flew out of the boat, and immediately it started running rough again. Restarted and problem stayed. It's a portable gas tank, fuel line seems to be OK. Any suggestions please?
 
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MadTom

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Any suggestions please? I know there are two fuel pumps on these engines. Not sure if the symptoms I see reflect on which of the two may be malfunctioning. Today I replaced the portable fuel tank and hose, different gas - problem remained.
 
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racerone

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Water pump impeller replaced ?-----What did the old plugs look like ?-----Oil level OK ? Replaced fuel filters ( 3 of them I think ) on this motor.-----Valve clearance checked ?----Did you hit something with the motor?
 
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MadTom

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racerone said:
Water pump impeller replaced ?-----What did the old plugs look like ?-----Oil level OK ? Replaced fuel filters ( 3 of them I think ) on this motor.-----Valve clearance checked ?----Did you hit something with the motor?
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Impellor has not been replaced but it is working. Old plugs did not look fouled. I did not replace the fuel filter this season. - I know of one of them so perhaps that is an issue, however I do not know where the other filters are. As far as having a marine mechanic look at it, this is the beginning of boating season and I've been told maybe late june or early July, according to the places I've spoken to. I did not hit anything with the motor. Thank you
 
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racerone

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I find at least 2 filters on these.-------I would look into the vapor separator.----Clean the tank and check float and float valve in there.-----Check IAC valve.
 
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MadTom

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racerone said:
I find at least 2 filters on these.-------I would look into the vapor separator.----Clean the tank and check float and float valve in there.-----Check IAC valve.
Click to expand...
Thank you for your time. I did swap out my tank, fuel and fuel line for another, no luck. You may have been correct about 3 filters:, the low pressure fuel filter which I have replaced before and that's next on what I can do myself, there is a fuel pump filter which I think is more internal, and then I think there is a high pressure fuel filter which I'm hoping you could confirm is pictured in the attached pic, which again I think I can replace myself but I am having a difficult time confirming part #. The black round filter housing in the pic has 8V27 printed on it but that does not relate to much. I do not know where the high pressure fuel pump, but I think it's internal, behind the manifold cover.......I've looked up how to check the IAC valve and if you could pint me in the right direction I would appreciate that as well.
 

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MadTom

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racerone , thank you again. Is there a link to a forum post here on how to check the IAC valve you could please forward me?
 
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MadTom

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racerone said:
High pressure pump is inside the vapor separator tank.
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I drained the VST , ended up with about 5 ounces of liquid of which over 50% was water, and a piece of debris was in there too. Replaced the low pressure fuel filter and the high pressure fuel filter. Used my neighbours gas tank and line and the issue seems to be fixed, however I could only go for a few minutes of a ride. My tank was filthy, so that is getting cleaned and dried and will be filled with marine grade fuel from the local marina rather than the high octane Shell V-Power. Fingers crossed and thank you again racerone.
 
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Crosbyman

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¸that is a lot of water.....if it came from bad fuel.... good.... just use clean fuel but VST's on modern ETEC anyway.... are also used to cool the fuel. On ETECs the fuel is used to cool injectors and it in turn gets cooled by the VST coil .

so make certain your VST water cooling coil if any... is not leaking from a small pin hole or corroded joints.
 
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MadTom

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Crosbyman said:
¸that is a lot of water.....if it came from bad fuel.... good.... just use clean fuel but VST's on modern ETEC anyway.... are also used to cool the fuel. On ETECs the fuel is used to cool injectors and it in turn gets cooled by the VST coil .

so make certain your VST water cooling coil if any... is not leaking from a small pin hole or corroded joints.
Click to expand...
Thank you. Not sure how to check if my VST water cooling coil is leaking. This is a 1999 Evinrude EL40 (suzuki engine DF40)
 
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Crosbyman

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plug one side (OUT) pump some air ... few PSI IN side....
spray soapy water all over look for bubbles. if you see bubbles it is leaking
 
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