Fuel Problems? 1985 40hp Johnson

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josh_scci

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OK the problem is the engine surges at WOT. No problems at idle or any other speed until I reach almost full throttle. Also it doesn't do it all the time. I have had the carbs cleaned and rebuilt gas tank fuel line and fuel filter have all been replaced. My next step is the fuel pump. It is still the VRO pump with the oil side bypassed and it is original from 1985. I have read where other problems can cause this so I would like some input.
 
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Monte1961

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Re: Fuel Problems? 1985 40hp Johnson

try squeezing the primer bulb when this happens? If it runs better then fuel pump. If it doesn't, then we need to do some more trouble shooting. Good luck Monte
 
J

josh_scci

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Re: Fuel Problems? 1985 40hp Johnson

I have tried that before with no effect either good or bad.
 
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josh_scci

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Re: Fuel Problems? 1985 40hp Johnson

Also this may be more of a bog down than a surge. It gets to WOT then drops back to nothing sometimes it surges back to WOT other times it just runs bogged down.
 
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Monte1961

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Re: Fuel Problems? 1985 40hp Johnson

How long since last tuneup?
 
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josh_scci

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Re: Fuel Problems? 1985 40hp Johnson

What specifically do you mean in "tune up"? Other than what was mentioned above nothing has been done in years except changing the lower units oil. I inherited this boat from my dad and he didn't really do much maintenance.
 
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Monte1961

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Re: Fuel Problems? 1985 40hp Johnson

Get New Carb/s Kits and overhaul them. Sounds like typical High speed circuits are in the process of plugging up. Good luck
 
J

josh_scci

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Re: Fuel Problems? 1985 40hp Johnson

Carbs where just completely cleaned and rebuilt last year by the shop and it has done this from day one out of the shop. I just couldn't afford to take it back for more service.
 
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Monte1961

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Re: Fuel Problems? 1985 40hp Johnson

well then I don't know what else to tell you! The only other thing I can suggest is, Try fogging the carb/s with a spray bottle filled with fuel/oil mix. When it acts up, spray carb/s and see if it picks up or bogs down. If it pics up, it will need carb work. If it bogs, there is another issue. Good luck
 
J

josh_scci

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Re: Fuel Problems? 1985 40hp Johnson

You don't think it could be a fuel pump that is 26 years old? I just cant afford $90/hr shop fees if its something I can handle since I already have to do some fiberglass work.
 
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Monte1961

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Re: Fuel Problems? 1985 40hp Johnson

Well you said you squeezed the primer bulb and it didn't change anything right? When you squeezed it, you override the fuel pump. But at 26 years old, who knows. Just for sh*ts and giggles, have you done a compression check by any chance? Post back results. Monte
 
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josh_scci

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Re: Fuel Problems? 1985 40hp Johnson

Not yet but it is on the agenda along with new coils, plugs, plug wires to name a few things. Ill post back as soon as I get my hands on a compression tester.
 
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Monte1961

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Re: Fuel Problems? 1985 40hp Johnson

As long as compression is within 10% of each other and 90psi, or better, it should run OK. When you do compression check, Have all plugs removed when testing. But I would try fogging the carb/s first, this way you will know if it's fuel related or electrical. Good luck and post results. NOTE: Overhauling carb/s is not all that complicated. and if you should need any assistance, chime in at any time. That's what were here for. Monte
 
emoney

emoney

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Re: Fuel Problems? 1985 40hp Johnson

As a heads up, most big box stores and especially a Harbor Freight carries basic compression test kits for around $10.00. It's a good thing to own.
 
J

josh_scci

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Re: Fuel Problems? 1985 40hp Johnson

OK i think I found a problem not sure if it would cause this issue or not but the oil input line on the VRO pump was not blocked off and would be a considerable air leak into the system. Would this cause a surge issue?
 
J

josh_scci

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Re: Fuel Problems? 1985 40hp Johnson

Anybody think that could be the problem? Also a lot of the fuel line seem to be held in place with zip ties instead of hose clamps and seem to be leaking some fuel.
 
R

Rick.

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Re: Fuel Problems? 1985 40hp Johnson

If they leak fuel, then they could also leak air into the line which could be the cause of the slow/fast rpm your having. Not sure about the vro plug but I imagine it would cause the same issue. In any case it is supposed to be plugged. Best of luck. Rick.
 
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