1999 Johnson 150 fuel mixture screw setting

Hi,

Does anyone know the correct settings for the carburetor mixture screw on 199 Johnson 150 carburetors. I cleaned and rebuilt the carburetors and reset the screws to the same settings but it seems like it is burning rich.

Thank You

What were they set at and what were the symptoms before your work? Of course it runs fine at high speed, right? Have you checked spark? Must have at least 7/16" arc nice crackling hot blue/white. Weak spark or low compression can cause low speed symptoms as you describe.

They were set out 6.5 and 7.5. I have done a lot of work rebuilding all the carbs including new bowls and float assy. 4 of 6 bowls were cracked.

When I bought the boat it always had a fuel smell, but the guy told me they changed the fuel line from the tank and sending unit, and the smell was from that. Needless to say further inspection I found many issues. fuel fill and vent hoses were leaking, and that was the bigger issue with the fuel leaks. Changed them flush the hull numerous times and no fuel smell. Replace the VRO, primer(both leaking, rebuilt all the carbs, replaced hoses and clamps. no leaks by the motor. New plugs and good spark (I checked spark today). So I have another string talking about the sputtering at low speeds. And I found the battery switch had failed and was not making good contact so the engine was not getting full power. The battery meters showed 12.8 -13.5 VDC. But yesterday it would not start like it had a dead battery. Long story short I traced it to the battery switch. I replaced that and the engines is running better. I did not get it out to the water for a good test yet, but atleast in the test tank she would idle without sneezing or coughing..... If I would have checked the spark before I fixed the switch I bet it would have been weak..... If I ever have a problem like that again (Hopefully not) I will check spark as one of the first checks. Thanks

They have to be set in the water,in gear and boat untethered. Initial setting is 5 turns out from a light seat and adjust from there...they cannot be adjusted on muffs.

I had them set at 5 and it was running rough in and out of water. I have since moved them out to 7 and it seems like it is running better. But when I had them at 5 I may have had a spark problem related to the failing battery switch. I will have to get it out to the water and run it and see.
We have some storms coming through so will have to wait a few days.

Thank You

Yes you will get effected by that tropical storm. When in the water, your exhaust has more back pressure at low speeds. Mixture requirement with that backpressure is normally a bit leaner.....why? More exhaust gasses are retained. Engineering is involved to help exhaust pulses time with subsequent detonations to expedite cylinder evacuation. That is the idea with expansion chambers. Example.....competition chain saws and most 2 stroke motorcycles. In case of your through hub exhaust, as boat moves forward, back pressure is minimized, as you backup your boat that's another story.

I have a 175 and my book says 4 turns to start if you have the book at the very end of fuel section it has a list of engines and needle settings

Jerry T said:

I have a 175 and my book says 4 turns to start if you have the book at the very end of fuel section it has a list of engines and needle settings

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Hi Jerry,

I have a seloc book, I did not notice that but will look again. Right now I have mine at 5 turns out and it seems like it is rich. I took it out to Axel reef a few days ago and it runs great at higher throttle but still runs rough at idle and every now and than a sneeze... I will check my book again and and or I may just wind then back to 4 and see how she goes.

They have to be set in the water,in gear and boat untethered. Initial setting is 5 turns out from a light seat and adjust from there...they cannot be adjusted on muffs.

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You have to set this way...Throw the Selco book away..