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Jeff G.
Jeff G., Marine Mechanic
Category: Boat
Satisfied Customers: 4716
Experience:  42 years experience, Certified Master Technician, All Major Outboards, Sterndrives, Hi-Performance
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My 90 HP Johnson outboard engine continues to idle too high,

Customer Question

My 90 HP Johnson outboard engine continues to idle too high, around 2300 rpm seemingly increasing to around 3000 I recently replaced what I believe is called a primer solenoid
Submitted: 5 years ago.
Category: Boat
Expert:  Jeff G. replied 5 years ago.
I will be happy to assist you. If you have a question or need clarification please post back at any time.
First make sure the primer is connected to the nipple behind each carb. You'll get a lean condition and high rpm's if it isn't.
Next find the throttle arm on the side of the engine.
Remove the remote control throttle cable from the throttle arm.
Make sure the throttle arm stop screw goes all the way back until it contacts the boss on the block. Don't adjust the screw, just make sure the arm goes back.
If you look at the carb linkage the roller from the carb linkage interacts with the throttle arm.
Make sure the carb linkage is all the way closed.
Remove the black plastic air silencer from the front of the engine. Look into the carbs at the brass throttle valves, the round plates. Make sure in idle, throttle arm all the way back that all of the carb's throttle plates are closed.
With the throttle arm all the way back, does the eye in the end of the throttle cable line up with the attaching point? If not adjust the cable by turning the thumb wheel where the cable anchors on the engine.
Do these check and adjustments and post back what you find.
Jeff G. and other Boat Specialists are ready to help you
Customer: replied 5 years ago.
Hi, I did remove the remote control throttle cable from the throttle arm and the idle speed went down to around 1200 still seems high, from the shop manual it seems to me the idle speed should be around 700? There is a lot of play in the throttle linkage the screw does not neccesarily stay against the boss, there is another roller on the throttle linkage that looked suspect and I have just found the remains of a rotted plastic bushing that would have been on that roller explaining the play in the linkage. If I back the throttle arm screw out and hold it against the boss with my finger the idle seems to drop a little more but the engine skips( this could be a seperate issue) I believe you can create a situation wher the engine is burning more oil than gas and I dont want to do any damage internelly the remote control cable comes in at a bit of an angle to the connecting screw.Can I assume that the primer is connected to the nipples on the carbs since the idle did drop?it looks like I have to take some things off the engine to get at the bottom carb nipple.
Expert:  Jeff G. replied 5 years ago.
You need to replace that plastic piece on the roller, they commonly rot and cause problems.
Turn the adjusting screw out a little to push the throttle arm against the block a bit more.
I am assuming you are doing this out of the water on the hose?
You need to adjust the idle speed in the water in gear. You need the water for backpressure on the exhaust tuning and in gear under load.
I don't pay a huge amount of attention to exact idle speeds. You just want the engine to idle as slow as possible in gear without popping or shutting off.
If it starts popping it is a lean condition.
Don't worry about the fuel and oil mix, it will not go too lean.
You can use the throttle cable to push the throttle arm stop screw against the engine.
Once in the water your rpm will drop 2-300 rpm.
Customer: replied 5 years ago.
OK I need to get that bushing then try this again. How would I adjust a lean condition? You mean adjust the throttle cable to hold the screw against the stop?Yes I am doing this on the hose, so I will expect the idle to be a little high based on what you said. What is exhaust tuning?Thanks.
Expert:  Jeff G. replied 5 years ago.
The engine is designed to run with the midsection partially filled with water. This created back pressure on the exhaust gases, so the engineers tuned the engine to have water in the tuner under the powerhead. This causes a higher idle out of the water.
Once you get the bushing then lets see what she does and then we can go from there.

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