87 johnson 70hp dies down at full throttle

C

clay123

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Jun 5, 2007
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I just took out and capped the oil injection side of VRO and now using premix 50:1. Today was the first day out using premix engine starts and runs fine except at full throttle. It goes for about minute wide open then it dies down revs up then dies down to idle. Runs good at 3/4 throttle. Whats happening?
 
jtexas

jtexas

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Re: 87 johnson 70hp dies down at full throttle

after it dies...is the fuel line still pressurized?
 
Big Keepers

Big Keepers

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Re: 87 johnson 70hp dies down at full throttle

Sounds like a restriction in the fuel line somewhere. Or it could be a failing VRO pump. I'd check the fuel lines first.
 
C

clay123

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Re: 87 johnson 70hp dies down at full throttle

as soon as it goes to idle I can throttle it back up, but after a minute at full throttle it dies back down to idle. The primer is a little soft when this happens but not completely. The engine did not do this before I removed oil injection from VRO. Could the premixed fuel (50:1) be causing this somehow? I am going to try putting in new fuel lines ,that seems like a good place to start.
 
jtexas

jtexas

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Re: 87 johnson 70hp dies down at full throttle

premixed fuel - no that wouldn't cause the problem...the VRO premixed the fuel before it got to the carbs so its getting the same diet, just a bit more oil at idle but same ratio at hi-speed, might smoke more than before - but try pumping the primer when the RPM's drop; if RPM's pick back up, its a sure sign the fuel pump isn't putting out enough fuel. If the bulb is getting sucked flat, means there's an obstruction upstream of the bulb.
 
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Big Keepers

Big Keepers

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Re: 87 johnson 70hp dies down at full throttle

That actually sounds about right, fuel pump. It can't hurt to swap the lines anyway too since ethanol likes to destroy them. I'd also replace the check valves in the primer bulb if they are a few years old already.
 
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