How to know if engine is running rich

Bry21317

Chief Petty Officer
Joined
Apr 9, 2002
Messages
552
I am just wondering, is there a way for me to tell if the engine is running rich? The engine is a 94 Mercruiser 305, it was upgraded over the winter to an Edelbrock Performer RPM Airgap Intake and a Edelrock 1409 Carb. It seems there is quite a bit of black soot building up in the Thru Hull Exhaust. This has only been from idling also. No higher, as I have been using it on the hose so far, will be lake testing in a few days.

Just wondering if this is a sign of it running to rich. I pulled the plugs the other day and they seemed ok.

Bryan
 

bruceb58

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Mar 5, 2006
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30,454
Re: How to know if engine is running rich

Does it bog or load up while idling? If not, I wouldn't worry about your idle mixture as much as I would running mixture. When you take it out, do a high speed run, slow the boat and then turn it off without letting it idle much. Pull some plugs and do a plug read.
 

Don S

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Aug 31, 2004
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Re: How to know if engine is running rich

I would do the test bruce mentions, but remember one thing. You have cooling water running thru the exhaust all the time. If the choke is set tight and you get a lot of smoke during warm up before the choke opens, all that black is going to be in the pipes and especially right at the transom (Coldest part of exhaust) and won't burn off. So it is ALWAYS black.
 

Bondo

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Apr 17, 2002
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70,464
Re: How to know if engine is running rich

Ayuh,.....

Those Carbs are easily adjustable,....
You can do a Plug Reading like Bruce says at different rpm levels to set the various stages of idle to WOT.....
 

Bry21317

Chief Petty Officer
Joined
Apr 9, 2002
Messages
552
Re: How to know if engine is running rich

The choke is set a little lean I think. It is on the 3rd tick from the back of the boat, when looking at the carb from the front of the motor.

I did have a little bit of bogging under load the other night right after Idel. I did not pull the plugs on the test run yet, but will do this. I think I need to tweak the carb some. So I am reading through the Edelbrock manual on how to set it.

The boat ran like a champ other than the bog on take off, which adjusting the idle mixture seemed to cure this pretty much. Just a big slow on take off now to get out of the hole. Other than that I runs like a scalded dog.

Bryan
 

bruceb58

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Mar 5, 2006
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30,454
Re: How to know if engine is running rich

Just remember that running too lean is worse than running a tad on the rich side.
 

FreeBeeTony

Captain
Joined
May 15, 2002
Messages
3,991
Re: How to know if engine is running rich

Can you explain the bog? I have a 1409 also and am experiencing a vibration around 1500-2500RPM........then it clears out.........I am in the process of trying different springs.........just picked-up a 1488 tuning kit.........gonna play tomorrow to get ready to fish this w/e.
 
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