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1983 Johnson 70 full throttle bog

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MTorre001

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I have a 1983 Johnson 70hp that is bogging down at full throttle starts right up and idles fine noticed that if I press in my key ingintion primer every sec the motor will run better but as soon as I stop pushing key primer motor will slow drastically! I have replaced fuel pump, all fuel lines and primer ball, rebuilt all 3 carbs but did not remove jets just soaked each carb in Berryman soak and blew out with compressed air. Have new fuel tank on order. Any suggestions would be greatly appreciated !!
 
Pull the suction tube out of the fuel tank and see if the strainer is dirty? Did you loosen or remove the cap on the fuel tank? Did you replace the pulse tube for the fuel pump also?
 
kimcrwbr1 said:
Pull the suction tube out of the fuel tank and see if the strainer is dirty? Did you loosen or remove the cap on the fuel tank? Did you replace the pulse tube for the fuel pump also?
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I will be replacing fuel tank today as my old metal tank has seized screws and I am unable to remove strainer to check. I have loosened fuel cap with no improvement, and I am not familiar with the pulse tube for fuel pump or its location
 
Did you use the same size for the pulse tube I believe it goes to the nipple on the bottom of the intake manifold? The pulse tube is smaller than the fuel lines and you may have a small leak is all it takes.
 
kimcrwbr1 said:
A smaller tube and as short as possible will give it a better pulse. What is the part number of your new pump?
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The current tube looks like 1/4 inch same as output also noticed the pulse tube has a spring in it. Is this spring necessary? The fuel pump is 0438559. I am going to get more fuel line today but want to get correct sizes
 
Did you figure out the problem mine is the exact thing


MTorre001 said:
I have a 1983 Johnson 70hp that is bogging down at full throttle starts right up and idles fine noticed that if I press in my key ingintion primer every sec the motor will run better but as soon as I stop pushing key primer motor will slow drastically! I have replaced fuel pump, all fuel lines and primer ball, rebuilt all 3 carbs but did not remove jets just soaked each carb in Berryman soak and blew out with compressed air. Have new fuel tank on order. Any suggestions would be greatly appreciated !!
Click to expand...
 
Pressing in the key to energize the Fuel Primer Solenoid and having the engine respond to run normal temporarily indicates that you have fuel being supplied to the fuel primer solenoid and the carburetors.

It also proves that fuel IS NOT flowing thru the carburetors as it should be. Engaging the Fuel Primer Solenoid is simply allowing fuel to BYPASS the carburetors... indicating that your cleaning of the carburetors was somewhat flawed.

Remove, if possible, and clean the high speed jets which are located horizontally in the bottom center portion of the float chambers... clean them carefully with a piece of single strand steel wire as solvent just doesn't do that job properly.

Fuel must flow freely thru this jet before it has access to any other fuel passageway... and being somewhat clogged, fouled, gummed, it will not allow the proper amount of fuel to flow at the higher rpms... the result being that the engine will seem to run properly at a low rpm but when you apply the throttle, the engine will fall on its face so to speak and die out.
 
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I agree 100% with Joe. These jets have to be PHYSICALLY cleaned to the exact original orface size. Otherwise you will destroy the motor by running it too lean. I have seen this happen an almost countless number of times and ethanol fuel certainly promotes this condition. If you took a poll on how many techs here use ethanol in their own marine, seasonal, and small engine equipment, it would probably be less than 10 percent. Ethanol is illegal to use in airplanes, I wonder why?
 
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