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Author Topic:   Tweaking Carb.To Correct Rough Idling(Novice Question)
wellsme posted 05-25-2004 02:01 PM ET (US)   Profile for wellsme   Send Email to wellsme  
Hello All,
I have a 1996 40 HP Mariner duel carb. four plug two stroke that just does not idle right. I replaced the fuel line last year, all the connections seem tight{no air leaks), new 12 gal. gas tank(vent screw open), fresh gas.
The motor will idle rough and eventually stall(even when warmed up). The motor seems to run very good at higher speeds. If I attenpt to adjust the carb. do I adjust both?
I'm not sure if this is smoething I should tackle. Any suggestions would be appreciated.
Thank you.
Bigshot posted 05-25-2004 02:58 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Before adjusting run a jar of Techron or Berrymans B-12 in the tank making sure to let sit overnight with it in the carbs. Try this for 1 or 2 tanks only and don't be surprised if it is worse while doing so and then clear up with fresh gas.
Chuck Tribolet posted 05-25-2004 05:07 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Follow big's advice.

Then when you go to adjust them, you need to adjust both,
and repeat and repeat. You'll adjust one, then the second,
which will change the idle speed a little, so the first one
needs to be adjusted, which will change the idle speed, ...

You generally want to be at "lean best idle" There will be
a narrow range (15-30 degrees) where the idle speed is the
same. You want to be at the clockwise end of that range.
If the engine bogs coming off idle, try the middle of the
range (I don't think these have an accelerator pump).


greyg8r posted 05-25-2004 11:13 PM ET (US)     Profile for greyg8r    

Why do you think it's a carb problem? How do you know it's not a spark problem? Or a compression problem? Unless you have ruled out these latter two, then don't mess with the carb(s); they MAY be fine.

Is it really running very good at higher speeds or is the miss just less noticeable. On my Evinrude, one of the 4 cylinders wasn't firing at all and I didn't know it at high rpms.


AQUANUT posted 05-26-2004 09:10 AM ET (US)     Profile for AQUANUT  Send Email to AQUANUT     

There are a few things you should consider, considering your comment "maybe this is something I should not tackle"

mercury school teaches...always check compression first.

experience teaches me...if your not a brain surgeon..don't operate on brains...

I recently seen two 200 hp mercury on a 26 outrage turn into the biggest black anchors..due to some mechanics that work on commercial jetboats "rebuilding" the carbs..and leaning out the engines...guess how much that cost to fix?

take it to a mercury certified technician. avoid further issues

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