Johnson 6hp only runs in wide open throttle

Sea Ray 220

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Jul 10, 2015
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I got a 6r74c Johnson 6hp. So far I rebuilt the carb, new coils/points, and replaced hard gasket. Compression is at 85. The only way it will start is in wide open position. When does start I have to hold throttle wide open and it’s barely running and not smooth. At one point it did smooth out and start to rev but then went back to having to hold throttle open. Also change fuel pump and plugs with fresh gas. Both cylinders seem to get spark. I’m at a lost here, no clue to what’s going on, any help will be much appreciated.
 

racerone

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Dec 28, 2013
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Two questions.-----Does spark jump an actual gap of 5/16" , yes or no ?----And did you remove / clean the high speed jet that screws horizontally into the carburetor bowl, yes or no ?
 

Sea Ray 220

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Yes I did remove the jet and it was clear. No I didn’t check to see if the plugs spark was that long. Are you saying it should arc 5/16 of an inch?
 

Crosbyman

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how about cleaning the top slow speed chamber under the dime size plug ?? done ???

proper gasket …. some have no holes to allow gas to flow UP to the idle chamber

see picture... older carb but same basic design to the upper slow speed chamber
 

tomhath

Master Chief Petty Officer
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Dec 5, 2007
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Was it running before you did that work?

My wild guess is that it's running way too rich. Maybe flooding from a float that's set too high. I'd go through the carb again.

Try starting it, then disconnect the fuel line and see if it smooths out for a little while before it runs out of gas.
 
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Sea Ray 220

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I bought the motor of a guy on Facebook market place. He only wanted a $150 for it but he said it ran. Of course no gas tank to start it. But I figured for $150 take a chance.

i went thru the carb twice, rebuild kit with new float, pin and seat. I soak the carb in acetone and another time in degreaser. Blew air thru it and seemed to be clear.

I replaced coils oils and points but I’m going to look at them again. Order a tool to measure the arc so I will see if it’s getting a good spark.

the odd thing for a moment it did take off and ran great for about 3 seconds.
 

Crosbyman

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does your gasket have a side hole to allow gas to flow up the top slow speed chamber under the dime size plug

nothing blocking the idle passage (broken screw tip) ??
 

Sea Ray 220

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Jul 10, 2015
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Yes the gasket does have a hole to allow gas. The idle passage is clear, check it several times.
 

Sea Ray 220

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Ok a update. I received the tool to check the arc and it’s very strong. 1/4 on both cylinders. Also I bought two new plugs. When I removed them to check the arc the top was a showed black coloring and the lower look like new. Something is blocking gas to the lower cylinder. Any ideas?
 

Crosbyman

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gas is sucked in either crankcase chambers (upper and lower) on the up stroke via the reed plates behind the carb…

maybe you do not have enough vacum (at lower RPM) to pull the gas fumes across the reeds due to a lower crankcase seal leaking air

others will comment

try putting a tea spoon of gas in the lower cyl. install the plug and start it up see what happens
 
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