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Jetting 1999 Force 120 HP

NE, Iowa??? Was the motor sold new in your area?
They install the jets at the factory and are supposed to jet according to the elevation.
But I don't really believe that?? :)

Any idea what jet is in there now?(both carbs)
Some carbs have a high and a low speed jet(the low can be covered with a plastic plug)

How does it run at high speed?

Test: Get the motor running, go for a ride.
Then run the boat at wide open for about 10 min.
Then at full speed turn the key off.
Don't slow down or pull the throttle back, just turn off the key.
Be careful around other boats(had to say that).
Then pull the plugs and check the burn.
Post pics if possible.

Test: get the motor warm, can of starting fluid.
Spray the sf around the intake side of the motor.
Any change in the way it runs??
Yes? then it's sucking air someplace.

Sometimes a small backfire or even a cough or stutter can blow one of the port cover gaskets.
That allows air in and it won't run right?

Timing: check the timing.

Set the air screws at 1 1/2 turn out and adjust in the water, motor warm and in gear.

Hope something here helps.
 
Jackfish1 said:
Has anyone done any Jetting with their outboard? Mine seems to run a bit heavy or fat. Plugs say so.
Click to expand...

Thank You for responding Jerry. I have not yet checked the Main Jet # yet...but will. The 1999 outboard was purchased from East Coast I am 2nd owner since 2004...motor was 5 years of age at that time. Currently the air screws are out 1 1/4 from light seat. Replaced inlet needles this spring and cleaned all jet/air passages properly. From all my 40 years of racing and riding 2 strokes reading plugs is a normal process. They read fat? Boat runs clean at WOT. Will get back to you.
 
https://www.boats.net/catalog/mercu...oard/1999/h120412vd-elpt/recirculation-system

The fuel recirc system and Ethanol
Ethanol can melt the inside of the hoses and the gunk can block the intake.
.
If the check valves are clogged, it can perform bad at slow speeds.
You can replace the hoses and spray carb cleaner in all the check valves.
#5/3/2 seems to get clogged worst.

Carb cleaners break up the carbon deposits and that can block the valves.

Setting the low speed air/fuel. You probably already know how, but.
Start in the water and get warm.
In gear at idle 750-800 rpm.
Top carb.
Pinch off the equalizer hose.
Then slowly turn in 1/8th turn at a time waiting 10 seconds between turns.
Repeat until it coughs, sputters, stalls etc. then back out 1/2 turn.
Repeat on the bottom
 
Jerry, I found it the timing advance set screw has been moving. Lock nut must have vibrated loose and allowed SS threaded bolt to vibrate or turn back. I checked and the mains are .88. Parts microfiche shows .88-.86-.84 & .82 as an option. I will leave them alone and get motor retimed. Going to run 16 ounces Sea Foam against 16 gallons NON Ethanol Gas. Keep posted.
 
Seafoam is like adding soap to your gas.(sf is useless,my opinion)

If you really want to add or put something in the gas.
Use Chevrons Fuel system cleaner.
Black bottle,looks like an upside down funnel.
Says contains Techron.

Mix 1 bottle of this with 1 gal. of gas add the extra oil needed..
Start and run this through the system.
It works great at cleaning the system.
Run for 20-25 min. and then let set for 8hrs.
Run it normal after that.

Bought a Ford Ranger fuel injected ran but not great.
Did the mix(no oil) and I could actually feel it run better as I drove down the road.
 
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