Topic: 1974 15hp Johnson wont idle – Antique Outboard Motor Club,Inc

This topic has 11 replies, 8 voices, and was last updated 9 years, 2 months ago by fleetwin.

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June 24, 2016 at 8:01 pm #4583
wick83
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So I’v rebuilt the carb and cleaned it 5 times motor will run with the choke half closed but at as high of an idle as it will go with the throttle. Motor will run like hell win gear wide open, it has great fire and good compression. It acts like the low speed adjustment needle is doing nothing, i seated it lightly while it was running and no change then I turned it way to far out to around 4 turns counter clockwise and still no change. Any ideas?

Forgot to add that when the idle side of the carb would normally be in control the motor will just shut down
June 24, 2016 at 8:45 pm #38905
lindy46
Participant
Did you remove the welch plug on top of the carb and clean the idle circuit? There are small passages under there that can clog. Also make sure to check the tip of the needle and make sure it’s not broken off in the orifice.
June 24, 2016 at 9:44 pm #38906
wick83
Participant
I did pull the plug and ceaned it very well and the needle looks great, carb cleaner flows through the idle circuit good.
June 24, 2016 at 9:58 pm #38907
frankr
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I have no real solution, just wondering–is the needle truly going all the way in to seat before backing it off?
June 24, 2016 at 9:59 pm #38908
frankr
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Or maybe the seat is buggered up?
June 24, 2016 at 10:03 pm #38909
frankr
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Carb bowl vent obstructed?
June 25, 2016 at 2:18 am #38929
rudderless
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Make sure that welsh plug is not leaking air.
June 25, 2016 at 9:24 am #38934
billw
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Does the carb throttle valve close all the way when you back off the throttle? Does it start to open at the right point of mag advance? Just wondering if the synch is right. Flywheel key sheared but off by just a bit? Sounds like you have a real problem, although those engines didn’t idle right, right out of the box.

Long live American manufacturing!
June 25, 2016 at 12:53 pm #38937
PugetSoundBoater
Participant
Did you check your ignition timing and carb sync ?

"Some people want to know how a watch works, others just want to know what time it is"
Robbie Robertson
June 25, 2016 at 5:31 pm #38948
fleetwin
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Are you sure it is running on two cylinders when you slow it down? Perhaps it is dropping a cylinder at low speeds…
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