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Discussion Starter · #1 ·
Hey guys I need some advice. I have a 1983 Evinrude commercial 40 HP tiller. It is a pull start two cylinder with one carb. Anyway it used to run fine, but at idle it would cough. So at idle I would pull the choke 1/10th out and it would smooth out. Anyway I ordered a carb kit and changed the float valve and seat, float, all gaskets. I soaked it and and cleaned it with carb cleaner. Now it will not idle without the choke on. I have played with the slow speed screw with no luck. As a last effort I opened it back up and put the old parts back in. If runs a little better but its not usable. It coughs and jumps and till it sputters to a stop. Any advice on why it will only run with choke half on at idle speed?
 

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A carburetor must have all passageways absolutely clean
or it will not function properly. From what you describe, you are having
to use the main jet in order to run at idle. Sounds as if the idle jet
passageways are still partially obstructed. When rebuilt and cleaned properly
an old carb will run as well as a new carb.

http://www.marineenginedigest.com/diy/carb.htm

Note the importance of removing the brass plugs that seal the smaller passageways.
Failure to do so will result in an incomplete cleaning of the small passageways.

Here's a rebuild with pictures...

http://www.catfish1.com/forums/showthread.php?11900-Carburetor-Rebuilding-With-Pictures
 

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I Love microskiff.com!
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Discussion Starter · #3 ·
your link mentioned a o-ring on the low speed idle screw. How do i get the old one out of the carb? Also do I put the new one on the screw and just let it get jammed in the hole as I thread it?
 

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If your carb has the o-ring style of seal, pry the old o-ring out with a toothpick.
Press a new one back in with the eraser of a small diameter pencil.
Don't use anything with sharp edges or points.
Put a drop of 2 stroke oil on the o-ring so it doesn't bind
when threading the needle back in place.
 

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I Love microskiff.com!
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Discussion Starter · #5 ·
Hey guys I got it to run pretty good. Idles fine. The only thing is it has a flat spot in the throttle. 3/4's throttle and full throttle are the same. I think I need to adjust the float so it gets more gas. any thoughts?
 

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Check your ignition timing.
From idle to full advance, make sure you fit factory specs.
Also check that the butterfly in the carb is opening fully.
After disassembling the carb, everything needs to be resynched.
 

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The current flat spot, and all your other issues may have initially been related to the air fuel ratio set screw(note this is not the idle adjustment) try backing it out a quarter turn at a time and check you results across the RPM range. Don't go further out than you need, or you'll be going through spark plugs like mad. Also, depending on if anyone has ever adjusted said screw before you may need to remove an insert/plug to access it(the insert was used to prevent such an adjustment when a motor was set to meet EPA standards).
 
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