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2001 50hp 4 stroke idle mistyre adjustment.

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bitsy4643

Contributing Member
2001 50 hp mercury 4 stroke idle mixture caps were missing when engine purchased. Can someone tell me the correct manner to adjust these idle mixture screws properly? Thanks
 
Service manual (at least the one I'm looking at) is a little convoluted on this matter.

It states: "Idle mixture screw adjustment is required when carburetor has been overhauled".

Then below that it states: "The idle mixture screw is NON-ADJUSTABLE - 1998 and later model years.

(now my manual was published in 1999 so they may have changed back to an adjustable idle screw post 1999)

In any event, if it's adjusted, you turn it in (clockwise) all the way until it's "lightly seated" - so when it stops turning, don't reef on it - "just tight" is all you need.

Then you "back it out" (counter-clockwise) 2 1/2 turns.

That gets you to your "starting setting" - from there you can do your fine tuning. This can take a little time and requires some patience to do it correctly - of course if it's running "ok" and you are good with that you need go no further but you may be running a little rich or lean which will ultimately cause an issue "somewhere down the road".

To fine tune, from your starting adjustment you turn "each screw" 1/4 turn (clockwise) one each carb (of a multi-carb set-up - you tune them ALL at the same time)- give the motor time to (adjust) to that adjustment - maybe 30 seconds or so is usually enough - if the motor is still running relatively smooth you adjust them all another 1/4 turn clockwise (so now you are 1/2 turn back in) - wait - continue this process until the motor starts to get choppy. Note how far you have turned in (say 3/4 turn - so started to "bog" at 1 3/4 turns).

Then back it out to the 2 1/2 turns and do the same thing "the other way", 1/4 turns going counter-clockwise until she bogs "the other way" - say that was at 3 turns out.

The middle of that (bogging) is 3 - 1 3/4 = 1 1/4 turns (cut in half) so 5/8 of a "turn" from either the highest or lowest point - so 5/8 of a turn above 1 3/4 (1 6/8) = 2 3/8 "turns" is the "mid point".

And it's always "advisable" to run a "hair rich", so call it 2 1/2 turns (and while that happens to be the starting spec, that's just a coincidence because I pulled the numbers out of the air) :)
 
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That aint even close....You have to sync the carbs with a carb balance tool(vacuum gauges) because when you increase fuel in one cylinder, it affects the vacuum in the adjacent one thru changes in rpms & mixture etc. Without a vacuum gauges you can't do it in the right sequence to balance them out...and it can't be done "by ear" or on muffs. Below is link to video on proper hook up and all 4 strokes with 2 or more carbs must be done this way..
https://www.youtube.com/watch?v=XqOfSMq1DlY
 
faztbullet said:
That aint even close....You have to sync the carbs with a carb balance tool(vacuum gauges) because when you increase fuel in one cylinder, it affects the vacuum in the adjacent one thru changes in rpms & mixture etc. Without a vacuum gauges you can't do it in the right sequence to balance them out...and it can't be done "by ear" or on muffs. Below is link to video on proper hook up and all 4 strokes with 2 or more carbs must be done this way..
https://www.youtube.com/watch?v=XqOfSMq1DlY
Click to expand...

And it takes a while to do. The boat has to be in the water.
 
confused on reply. Video is showing balancing vacuum, not idle mixture screw adjustment. Is post explaining idle mixture adjustment correct and is vacuum adjustment of carbs not related to idle mixture adjustment? Sounds as if vacuum balancing is not related to idle speed adjustment as first post indicated. Please clear discrepancy. Thanks
 
thanks very much. did not consider idle mixture was affecting synchronization vacuum reading. Makes perfect sense. Thanks again
 
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