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lean -rich setting, 15 hp evinrude?

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  • lean -rich setting, 15 hp evinrude?

    okay so i bought an 81 evinrude 15 horse power .been trying it out for a couple days now.have a question i hope one of the wise men might be able to shed some light on.i,m very happy overall....but when i,m idling along and adjust the lean rich knob to get a smoother low idle and then i,m ready to crank her wide open,she will stall and bog down unless i adjust the lean rich knob all the way back to rich before i crack the throttle.i,ve owned two other outboards in my life and niether one was affected by the lean rich knob when it came to cranking it up for wot.if i was a betting man i would venture to say that i should probably have the carb rebuilt.any idea how much the average marine mechanic would charge to rebuild a carb...if i took it off myself and brought it to him? thanks in advance for any info diggerdan.


  • #2
    Re: lean -rich setting, 15 hp evinrude?

    Hello Dan. Being a new engine to you, probably wouldn't hurt to check the carb out....along with other items like pump and stat.I've noticed that you can lean these engines out enough that when you hit the throttle, they can bog until the fuel flow catches up.Why not do the carb job yourself? Save the extra money for a six pack? These carbs don't require any voodoo or magic enchantments. A generic service manual would do you well. It's as easy as removing the recoil starter and then removing the carb. OEM carb kits is around $15 American at your local John/Rude dealer.
    When in doubt...use the manual

    Rayland, Ohio....Along the Muddy Banks of the Mighty Ohio River.

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    • #3
      Re: lean -rich setting, 15 hp evinrude?

      sounds like a good idea....would a seloc tune up and repair manual be a good idea or is there a better one?

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      • #4
        Re: lean -rich setting, 15 hp evinrude?

        OH yeah Dan. OME mauals are the best cause they give you specific info on your engine. Search up Ken Cook Co., the outboardwizard or Marine.com. They all sell reprints of the original service and parts manual.
        When in doubt...use the manual

        Rayland, Ohio....Along the Muddy Banks of the Mighty Ohio River.

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        • #5
          Re: lean -rich setting, 15 hp evinrude?

          Diggerdan17, I'm in Prince George, drop me an email @ snowdrggn@hotmail.com and I'll let you know how to get a hold of me. These are simple carbs and the engine is very easy to set up. You should set up the linkages properly on it also as that can effect the throttle response. Give me a holler and I'll give you a hand with the little critter. Cheers, Snow. (Cam)

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          • #6
            Re: lean -rich setting, 15 hp evinrude?

            Snowdrggn, We've got a slightly newer version of the same motor ('86) and I rebuilt both the carb and fuel pump because it was hard starting at times. I had to remove the carb again and raise the float level slightly as it still wasn't right but now starts perfectly. Diggerdan17, the carb kit (from any dealer) is only about $15 and comes with pages of detailed instructions btw. Anyway, I've also noticed the bog from slow speed to fast and adjusting the mixture knob does effect it. I'm also interested in any other tips that'd help cure that slight bog so could you post it here?

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            • #7
              Re: lean -rich setting, 15 hp evinrude?

              thanks snowdrggn..i,ll give you a shout via e-mail...the wifes got me painting the basement suite so i might not have time to tinker with her for a couple of days

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              • #8
                Re: lean -rich setting, 15 hp evinrude?

                joaklay, It seems that a large part of the bog situation is an issue with the diameter of the venturi. It is relatively large for the volume that is drawn through it at low rpm. When you open the throttle quickly, the velocity through the venturi is drasticly reduced, thus reducing the pressure differential between the low pressure side of the venturi and the float chamber causing a "lean stumble" as the fuel flow into the throat of the carb is reduced at this point. It is quite basic physics. Richening the low speed side reduces this situation somewhat, but also causes it to run "fat" at idle. Another operational work around is to partially open the throttle initially to allow engine rpm to rise to a "fast idle", thus maintaining a reasonable velocity over the venturi to support good fuel mixing in the carb throat. Basicly, open the throttle in a smooth fashion allowing rpm to rise as you do so, the higher the rpm gets, the faster you can roll open the throttle. If the area of the venturi was reduced, you would have better fuel atomization at lower rpm with the throttle plate in the open position, but not enough air flow to support the engine at high rpm ( one of the critical differences between the 9.9 and 15hp) and end up with a lower WOT rpm, the lower net HP being developed. A richer low speed mixture will make for easier starting, particularily when cold, but will be detrimental for extended extreme low rpm operation. Some of the bog can be eliminated with careful setup of the corelation of timing advance and throttle actuation/initiation. This throttle "stumble" or "bog" is what led motorcycle manufacturers to utilize "variable venturi" or "constant velocity" carbs on modern motorcycles.THE SHORT VERSION: Use careful setup to eliminate some of it, and your wrist to get around the rest.Or...... Get a 9.9 which has a smaller carb. Cheers, Snow.

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                • #9
                  Re: lean -rich setting, 15 hp evinrude?

                  Hi Diggerdan,Maybe I'm heading in the wrong direction here - but when you say 'the lean/rich knob' are you referring to the knob by the choke pull? - Or the knob on the portside of the engine cowling?The knob by the choke is for setting the low speed mixture for smooth idling, and shouldn't need any adjustment after it's been set. It is not something you need to constantly adjust while you're running or idling - once you've set it right, it should be left alone.The knob on the portside cowling isn't a lean/rich knob - it's a slow idle adjuster, meant for altering your trolling speed. And when you've been trolling for a while, your motor will quite likely bog a bit before picking up revs.One easy test is this - after it's bogged and you've revved it under load for a few moments, let it drop back to idle and then open the throttle again. Has it cleared itself? If it has, then you don't seem to have a carb problem - you've just got a motor that gets slightly over-rich while idling for a while. A lot of motors do that.

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                  • #10
                    Re: lean -rich setting, 15 hp evinrude?

                    yes ,i,m talking about the knob by the choke. it seems weird to me that this would affect my engine when i go to wot from trolling ....but it will stall everytime unless i adjust the knob all the way to the rich setting before i "get up and go".

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                    • #11
                      Re: lean -rich setting, 15 hp evinrude?

                      Whjen you say 'all the way to the rich setting' are you meaning that you turn the knob in (clockwise) as far as it will go?So what happens to the idle if you leave it at this 'rich' setting? Does the motor idle OK?The knob can be pulled off the spindle. Pull it off, carefully wind the spindle all the way in, then back it out about one full turn and put the knob back on at its midway point (that is, midway between the two stops). The one full turn should be a rough setting for a normal idle. You can now fine tune the setting with the knob once the motor's warm, and if you don't have air leak or carb troubles the motor should idle and pick up ok.If it still doesn't idle and pick up ok, you need to start on the fuel delivery/carburetor setup as discussed above.

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                      • #12
                        Re: lean -rich setting, 15 hp evinrude?

                        Hmmm, actually, turning the low speed mixture knob 'Counter-clockwise' is making the mixture more rich. Clockwise makes the mixture lean....
                        Light travels faster than sound. This is why some people appear bright until you hear them speak.

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                        • #13
                          Re: lean -rich setting, 15 hp evinrude?

                          yes ,i agree...turning the knob counterclockwise makes mine run rich.

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                          • #14
                            Re: lean -rich setting, 15 hp evinrude?

                            Apologies for that ... Xcusme's got it the right way. Here, they all signal left and turn right, stop on the green and blast across the red - it's kinda catching!Now we've got that straight, have you tried what I suggested? If you have, what was the result?

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                            • #15
                              Re: lean -rich setting, 15 hp evinrude?

                              Lefty loosy, Righty tighty.....Suck, Squish, Bang, Blow....It's all we need to know......Cheers, Snow.

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