Setting Final Idle Speed and Mixture Procedure on Merccarb

[halcrimm]

Good evening all,

Mercruiser 3.0L Alpha 1 Gen 2 I/O.
S/N OD714746 Engine
S/N OD671270 Transom
S/N OD665768 Drive

So my new tachometer showed up today and I will be finally trying to set the idle speed this weekend. Reading through the procedure and have a few questions.

Step 1 - Connect an accurate shop tachometer to engine. (I am hoping the new tach for the dash will be okay for this seeing as I will have a buddy on the helm so it is not left unattended. Safety first)
Step 2 - If new or rebuilt carburetor has been installed, turn idle mixture needle in (clockwise) until it lightly contacts seat, then back out needle 1-1/4 turns. (Got it)
Step 3 - Start engine and run at 1500 RPM until engine reaches normal operating temperature. (Assuming I can be sitting at the dock with engine running, no need to be in forward gear moving. Right?)
Step 4 - With boat in open water, place remote control in forward gear, idle position. (Not sure what this means. I get forward gear and I get idle position. What is forward gear and idle position?)
Step 5 - Disconnect throttle cable barrel from anchor stud. (Do not understand what the purpose of this step is)(I will do it but I would like to understand)
Step 6 - Adjust idle speed adjustment screw to obtain 550-600 RPM, in neutral gear. (So once I remove the throttle cable I put shifter back in center neutral?)
Step 7 - Adjust idle mixture needle (Got it and makes sense.)

Any help is appreciated.
Thanks
Hal

 

[achris]

Re: Setting Final Idle Speed and Mixture Procedure on Merccarb

Good evening all,

Mercruiser 3.0L Alpha 1 Gen 2 I/O.
S/N OD714746 Engine
S/N OD671270 Transom
S/N OD665768 Drive

So my new tachometer showed up today and I will be finally trying to set the idle speed this weekend. Reading through the procedure and have a few questions.

Step 1 - Connect an accurate shop tachometer to engine. (I am hoping the new tach for the dash will be okay for this seeing as I will have a buddy on the helm so it is not left unattended. Safety first)

It won't be. You need a proper shop/accurate tacho. Someone posted up a link to a very nice digital 'contactless' tacho. (and only $16!!!)

Here's that link -> NON Contact Tach Tool RPM Handheld Digital Photo Laser Tachometer Tester | eBay

Step 2 - If new or rebuilt carburetor has been installed, turn idle mixture needle in (clockwise) until it lightly contacts seat, then back out needle 1-1/4 turns. (Got it)
Step 3 - Start engine and run at 1500 RPM until engine reaches normal operating temperature. (Assuming I can be sitting at the dock with engine running, no need to be in forward gear moving. Right?)

All they're after is for the engine to be properly warmed up and temperature stable and the choke fully open before you start doing the adjustments. If you need to move off and just run around at 1000-1500 revs for 10 or so minutes, it's not going to hurt anything.

Step 4 - With boat in open water, place remote control in forward gear, idle position. (Not sure what this means. I get forward gear and I get idle position. What is forward gear and idle position?)

Just in forward with no throttle on... Idling in forward.

Step 5 - Disconnect throttle cable barrel from anchor stud. (Do not understand what the purpose of this step is)(I will do it but I would like to understand)

It's because if the cable is out of adjustment it can hold the throttle open slightly, making it difficult to set the idle speed.

Step 6 - Adjust idle speed adjustment screw to obtain 550-600 RPM, in neutral gear. (So once I remove the throttle cable I put shifter back in center neutral?)

No, adjust the idle speed with drive in forward gear.

Step 7 - Adjust idle mixture needle (Got it and makes sense.)

As you adjust the mixture, the idle speed might climb a little. If it does, bring it back to 550-600...

Any help is appreciated.
Thanks
Hal

Hope this is enough help...

Chris.....

 

[halcrimm]

Re: Setting Final Idle Speed and Mixture Procedure on Merccarb

Chris, Thanks for the help so far. Maybe I should have started with the preliminary Idle Speed and Mixture.
Hoping to go out tomorrow to set the final idle (if my neighbor has a shop tach). I adjusted the carb using the preliminary Idle Speed and Mixture procedure from the manual.
I did order the contactless tachometer that you pointed out. Should be here on Tuesday/Wednesday. I also installed the new dash tachometer and it was nice having a working gauge. The new tach read about 550RPM at neutral idle and forward idle. I still wanted to adjust the carb correctly so I followed this procedure.

Step 1 - Back out idle speed screw until it no longer contacts idle cam. Turn idle speed screw in until it just contacts idle cam, then turn screw in an additional two turns. (Done)
Step 2 - Turn idle mixture needle in until lightly seated, then back needle out 1 1/4 turns. (Done)
Now the engine starts fine but idles, read from the dash tach, at around 1050-1100 rpm.
Is this an expected prelim idle to move into the Final Idle Speed and Mixture procedure under load.
I was just surprised that it doubled from prior to making any adjustments.

Hal

 

[sti1471]

Re: Setting Final Idle Speed and Mixture Procedure on Merccarb

I am in the process or adjusting my idle on my 3.0L mercarb as well. I set my idle to 700 on the trailer. when I took it to the water a few days ago all, the engine idles ROUGH and the engine was shaking as it seemed to idle at 400 in the water. so I set the idle to 700 in the water but it was still idling rough. I have not started it on the trailer since to see if the RPM doubled, but my guess is it did since I have to turn the idle screw just over 1 full turn or so.

Maybe I adjusted something wrong, but mine seems to have done the same thing yours did.

 

[achris]

Re: Setting Final Idle Speed and Mixture Procedure on Merccarb

....
Now the engine starts fine but idles, read from the dash tach, at around 1050-1100 rpm.
Is this an expected prelim idle to move into the Final Idle Speed and Mixture procedure under load.
I was just surprised that it doubled from prior to making any adjustments.

Hal

If the engine sounds like it's actually running at that speed, just screw the speed screw out a bit.... until your happy with the speed.

Remember, these are preliminary adjustments. Enough to get the engine running, nothing more. You then adjust the screws from there.

Chris......

 

[halcrimm]

Re: Setting Final Idle Speed and Mixture Procedure on Merccarb

Thanks Chris,
I just wanted to make sure that the Tach RPM is okay for rough set of idle. I will go on the water and adjust for final. Just wanted to make sure that I wasn't hurting anything.
Hal

 

[achris]

Re: Setting Final Idle Speed and Mixture Procedure on Merccarb

Thanks Chris,
I just wanted to make sure that the Tach RPM is okay for rough set of idle. I will go on the water and adjust for final. Just wanted to make sure that I wasn't hurting anything.
Hal

For a rough setting (or until you verify it), the dash tacho is absolutely fine....

Chris........

 

[halcrimm]

Re: Setting Final Idle Speed and Mixture Procedure on Merccarb

Got to take the boat out tonight (finally) to set the final idle speed. It was very easy to do. I also cleaned the flame arrestor really well prior to getting under way. Long story short, the engine is running super and I did not stall a single time going through the no wake nor coming back in at the boat launch. Feels good to know that i will get to take family out in our boat for the neighborhood labor day boat outing instead of us hitching a ride with friends. Thanks for everyone's help.