91' Bayliner w/ 91 Force 120hp L-Drive. Trouble gettin past 3800 RPM's.

[Open Waters]

First trip out since replacing the starter (boat sat for 2 weeks). After warm up, I had it running for bout 15-20 minutes (flirted w/ 5000 RPM's for a few minutes and ran fine) and then stopped to swim. Got done swimming and started it back up. This time I couldn't get her past 3800 RPM's.

I'm running rich (both air screws turned 1/8 turn counter clockwise from center) and had recently turned the drive throttle (screw w/ nut) a hair clockwise when trying to diagnose my previous starting problem (later found to be a bad starter)

Bad fuel?

Any suggestions?


Open Waters

 

[jerryjerry05]

Re: 91' Bayliner w/ 91 Force 120hp L-Drive. Trouble gettin past 3800 RPM's.

!Same prop??
1/8th turn from center????If the air screw is wrong you could have burned a piston.
Should be to the bottom(gently) and then out 1 and 1/16th turn.
Then in the water,motor warm and in gear.
Turn in till the motor bucks.coughs/dies.Then out 1/2 turn.Then adjust the throttle to 750-800RPM's in gear.Then rest the air again/
For the othe rproblem.
Do a compression test.Then a spark check.
The fuel pump might need a new diaphram.Or a line is collapsed.Water in the gas.
Possible ignition problems:no spark or weak spark after 3000rpm.Go to outboardignition.com and check the tests for your motor.

 

[Open Waters]

Re: 91' Bayliner w/ 91 Force 120hp L-Drive. Trouble gettin past 3800 RPM's.

Please explain the differance between the idle mix screws (air screws) and the throttle stop screw with jam nut (stop nut). How does one's pupose (significants) differ from the others'.

Also, what is the little white rubber screw/piece that is caddy cornered to the idle mix screw on the carburetors?

Thanks for the help.

Open Waters

 

[Sprky]

Re: 91' Bayliner w/ 91 Force 120hp L-Drive. Trouble gettin past 3800 RPM's.

If the motor did not die while you were at speed before you shut it down, you did not "burn" a piston.

If the motor shut down while you were at speed after your restart then there is the possibility of a damaged cyl.

The problem could be anything.... a stuck float, trash in the carb, bad electronics, damaged fuel pump diaphram, fouled plug etc.

Mixture screws will not cause it to not run at max speed.

Determine whether or not you have spark to all your cylinders.

Make sure plugs are not fouled...............Look for a plug or plugs that are different in appearance.

Pull the bowls off the carbs and look for debris.

Disassemble the fuel pump and look for damaged diaphram...............

Trouble shooting is nothing more than the process of elimination, keep removing variables and you will eventually find the problem.


Chris

 

[jerryjerry05]

Re: 91' Bayliner w/ 91 Force 120hp L-Drive. Trouble gettin past 3800 RPM's.

Air screw vs idle stop screw.
The idle stop screw is where you adjust the idle rpms.
It's on the bottom of the towershaft.Pic#2
The air screw,front or side of the carb.Is for adjusting the air/fuel mixture while at idle.Pic#1 #19 in this pic.
It will have a spring around the screw.

 

[Sprky]

Re: 91' Bayliner w/ 91 Force 120hp L-Drive. Trouble gettin past 3800 RPM's.

Your motor requires (X) fuel/air ratio to idle. The mixture screws control the amount of fuel that is added to the air flowing thru the carb for that ratio. The idle stop screw controls how far the butterflys open.... along with advancing timing.

As the stop screw is turned in, it opens the butterflys which allows more air into the engine. With that air, the mixture screws are adding the appropriate amount of fuel.

The mixture screws "trim" the ratio, The stop screw determines how much/little of that ratio the motor gets.

Chris

 

[pnwboat]

Re: 91' Bayliner w/ 91 Force 120hp L-Drive. Trouble gettin past 3800 RPM's.

The little white plastic screw by the idle mixture screws is a plug for a jet in I believe the idle circuit passage. Only time you need to remove it would be to change the jet or cleaning. Otherwise it should be left alone.

 

[Open Waters]

Re: 91' Bayliner w/ 91 Force 120hp L-Drive. Trouble gettin past 3800 RPM's.

Are the idle mix screws (air screws) suppose to be on the same setting, i.e. both rich, both middle, both lean. I would assume it differs from motor to motor. However, you know what happens when you assume.

By the way, thanks to all for the advise. To a rookie boat owner (2 months as of last week), small adjustments can seem stressful. Especially with the wife knowing that "buying the boat was the worst mistake"

 

[jerryjerry05]

Re: 91' Bayliner w/ 91 Force 120hp L-Drive. Trouble gettin past 3800 RPM's.

Adjust the air screw like my first post says.They could be off a bit from each other but will be very close.Don't try to match them.One passage might be drilled larger or cast a bit different.
Profile?? You might be close to someone who can help.

You do a compression/spark test?J