Adjust air/fuel mixture 3cyl mariner/mercury 60hp

[tikki]

Hello.
How do you adjust the air/fuel mixture screw on the carbs?
it is a mariner 60hp 3 cyl 1994

i dont have any rpm gauge.
i have adjusted all three carbs 1 and 1/4 turn out. and it seems to run good. but i am not satisfyed the engine has ruined smoother before on idle.
i have tried to adjust the top carb screw and the others a bit out or in. but i can't hear any difference.

any good ideas?

 

[quicktach]

Better slightly rich than lean. Get yourself a manual for the motor and follow it.

 

[ondarvr]

Give the screws a twist, you can't hurt anything, it will either run better or worse, and you can always start over.

 

[oldboat1]

getting a manual is good advice (above). Merc guys may see it differently, but I look to adjust air/fuel for leaner running to smooth out. 1/8 turns clockwise, waiting for engine to respond between adjustments. And like ondarvr says, can start over if not satisfied. Kind of like a reboot.

 

[bruceb58]

Depending on the carb, the mixture screws adjusts the idle mixture only. You have to change jets to change mixture at anything other than idle RPM.

 

[tikki]

No Title

number 24 in the picture. Think it is air/fuel mixture. the other nozzles is "19 Main (fuel) JET," and "20 Vent JET."

i have the manual but does not say anything about adjustment. just 1 and 1/4 turn out is the basic.
do i adjust all of the carbs 1/8 turn out from the basic adjustment. or just one at the time?

Tried to do this yesterday but did not notice any change.

 

[Faztbullet]

First...you cannot adjust these on a hose, need to be in a barrel or backed into the water. Second start with engine warm and adjust bottom carb first,middle next and top last. Turn in slowly till engine lugs and turn out till its smooth then add 1/4/ turn to this setting...

 

[tikki]

Thank you. the boat is on the water all year long so no problem there.

 

[Texasmark]

If you invest in a manual you will read that the proper way to adjust the low speed jets it to set them as lean as you can with the engine taking the load in the hole shot. If you are too lean on any cylinder you will "bog" in the hole shot...what is that? When you clear the no wake buoys leaving the dock, you firewall the throttle. You expect the boat to respond vigorously and arrive on plane (on top of the water, not in it) in a minimum amount of time. If you get less from your engine you have something wrong and that something could be a variety of things, maladjusted low speed jets for one.

 

[bruceb58]

If you invest in a manual you will read that the proper way to adjust the low speed jets it to set them as lean as you can with the engine taking the load in the hole shot.

He has idle jets. These are not LOW speed jets...they are IDLE. They will have nothing to do with getting up on plane unless the engine has loaded up from being too rich.

 

[tikki]

The boat is running good in full speed. but when i put it in neutral is sometimes dies.
i can se a lot of fuel or oil in the water when in idle.
i have adjusted the carbs to the basic setting 1 and 1/4 turn as in manual.
it is on these settings the engine will start easy. and runs almost perfect. but sometimes it stalls.

 

[tommarvin]

The engine should never die or stall,

What is the correct RPM at idle, We have a force 125, The RPM is supposed to be I think 750RPM when you just put it in gear.

A little rich is better than a little lean, the motor will last longer, don't lean out the idle to smooth it out.

My guts telling me your to lean.

 

[ondarvr]

Running lean at idle will have no affect on longevity, it will only influence how well it idles.

 

[bruceb58]

Running lean at idle will have no affect on longevity, it will only influence how well it idles.

+++++1

 

[oldboat1]

^^^can seem counterintuitive to lean it out, but that initial fuel/air setting may be too rich -- can cause stumbling at idle or when throttling down to idle. Unburned fuel at idle could indicate the fuel/air mix is too rich, though fuel/oil ratio more typical. Factory specs for the latter, but the fuel/air mix takes some tweaking.

 

[Texasmark]

Depending on the carb, the mixture screws adjusts the idle mixture only. You have to change jets to change mixture at anything other than idle RPM.

Not so sir!

 

[bruceb58]

Not so sir!

If it's the carb he shows in post #6 it definitely is the case. Hence why part #24 is called the idle needle.

 

[Texasmark]

He has idle jets. These are not LOW speed jets...they are IDLE. They will have nothing to do with getting up on plane unless the engine has loaded up from being too rich.

"Idle Jets" are the variable low speed jets which supply the engine with fuel until the rpms are high enough to cause a high enough vacuum through the carb's venturi to activate fuel flow through the high speed jet which is a fixed orifice in a brass plug.

The engine uses 2 jets per carb, not a third set dedicated solely for idle speeds on the order of 675 +/- 50 rpm. The addition of the high speed jet's fuel supply occurs at/above/around 2500 rpms on most current day engines which is an "at/on plane" attitude for most reasonably light weight, adequately powered, planing hulls. Therefore as is stated in print and is the practice of numerous operators/mechanics(assumed) of such, if adequate fuel is not supplied to the engine via the low speed jet, the engine will lug upon firewalling in the hole and planing speeds will not be attained. Now how do you suppose I know that?

Idle speed is set by either fuel/air mixture flow via venturi butterfly position or by varying the engine timing. A spring loaded set screw on the throttle linkage makes the adjustment independent of the remote control position. My 90 of the series used ignition timing.

 

[bruceb58]

Actually, I mispoke before. He does not have an idle jet because there is no such think as an idle jet.

Once the throttle plate open ever so slightly, little or no fuel will be supplied by the idle circuit which is controlled by the idle needle. There is a vacuum cause by the butterfly being closed that pulls the fuel from the idle circuit. once the butterfly opens, no more vacuum is present there so no fuel will come out.

We are talking about the same thing right? #24 in the diagram?

I agree with you that some carbs may have a low speed nozzle with a needle that adjusts it but according to his diagram, this one does not.