Idle Screw Adjustment ???

[jfholijr]

On my 1975 Merc 650 65 horse 3 cylinder outboard I think the best Idle position that I've been able to find is 1 1/4 turns out from lightly seated. Does this sound right?<br /><br />When I'm trying to adjust them at about 1 complete turn out the rpm's go up but as soon as I back off to 3/4 it dies and anything less than this will not work either. The 1 position is not right either because my rpms wile in gear will be 1000 no matter what and the out of gear will run 1500 - 2000. The only other direction I could go was to 1 1/4 mark to make it idle, but won't this be extremely rich? According to the manual I should be somewhere between the 1 and whereever it leans out at but like I said anything less than the 1 turn mark and it dies.<br />I know that all my other adjustments are correct i.e. timeing, advance, carbs have just been rebuilt etc. . Does anyone elses outboard use settings that are more than a turn out?

 

[schaiss]

Re: Idle Screw Adjustment ???

Have you done a complete cleaning on those carbs recently? A gallon of carb dip is only $12 at a local auto parts store. 1-1/8 to 1-1/4 turns out on your idle adjustment screws does not seem unreasonable. This adjustment should be done with the engine up to temp and in gear with no throttle.

 

[jfholijr]

Re: Idle Screw Adjustment ???

Hi Aquasportser, yes as I stated the carbs have just been rebuilt that is why I'm having to adjust the idle mixture screws, also this is with the boat in the water properly warmed up and in gear without any extra throttle. Just seems that it should idle a bit better than it is i.e. a little smoother. Also as I throttle up slowly it is still a little ruff untill I get past the idling curcuits and the high speed jets kick in then all is well.

 

[jim dozier]

Re: Idle Screw Adjustment ???

Nevermind

 

[jfholijr]

Re: Idle Screw Adjustment ???

Anyone else have advice? Greatly appreciated.<br /><br />Oh and also are both my carbs supposed to have the same settings or will they vary some?

 

[Chris1956]

Re: Idle Screw Adjustment ???

Whohoo, First of all the two carbs will likely have different idle needle settings. This is due to wear, float adjustment, cylinder and reed valve condition etc. It is also due to the fact that gravity(on the fuel) causes the cylinders on the top part of the motor tend to run leaner than the bottom ones. I find that if the cylinders have the same compression and are in the same running condition it is easier to adjust the idle needles. If they differ, it is difficult(sometimes impossible) to find the correct settings.<br />Remember that the ide needles should be set as rich as possible, since the carbs do not have an accelerator pump. Adjust (with fresh fuel) the needles in gear at the minimum idle speed, that it will still run. If it stumbles or wont accelerate, richen it up.

 

[jfholijr]

Re: Idle Screw Adjustment ???

Thanks Chris, My compression is 1 = 155, 2 = 154, and 3 = 151.

 

[agrazela]

Re: Idle Screw Adjustment ???

Whoohoo,<br /><br />I have a 78 70hp 3-cyl. After rebuliding the carbs, I find that my ideal idle settings are:<br /><br />Top: 1-1/4 turns out<br />Bot: 1-1/8 turns out<br /><br />The engine will die if I turn either to less than 7/8 turn out.<br /><br />My compression readings are also all between 150 and 155 psi.

 

[remmer38]

Re: Idle Screw Adjustment ???

Try 2 and a half. Better rich than lean. Trust me.

 

[starflt1701]

Re: Idle Screw Adjustment ???

Why better rich than lean? If the mixture is rich, won't that cause the motor to "load up" and rumble and shake at plane off?