Lean condition????@ idle??

[Boat Doctor1]

Heresone -cant figure out!! Merc 1000 - 100 HO 4 cylinder. Somewhat hard to start after primed - when starts - warmed up- put al idle- carbs seems to have a "Lean Condition" Seems like only on 2 carbs!! Lower 2 actually (4 carb engine) Been thru carbs- nothing found upon cleaning!! Same type condition!! Spark great on static & optical spark testers!! Runs great above idle. Someone told me this engine only runs on 2 of the 4 carbs @ idle!! Say What?? Anyone hear of this before?? Any factory explanation of this or differencense in fuel systems? If I induce fuel into bottom 2 carbs - symptoms of being lean go away! Fiel levels set great & nothing found!! I did get curious on top 2 carbs =only --- have idle mixture needles on them?? Anyone = serial #= B376687--- Help please!

 

[flyingscott]

Absolutely normal the motor is designed to idle on 2 cyl other 2 kick in at about 1700 rpm then you are running on all 4. They accomplish this by eliminating the idle circuit in 2 carbs these carbs have accelerator pumps. They called it a 2+2 motor it is a great idling motor smoother than most of the other 4 cyls of the time

 

[Boat Doctor1]

Ok as I was told-yet what could be causing a lean condition @ idle.??Carbs are =NOT dirty or stopped up.! Is there any fuel feed on carbs with the acclerator pumps @ idle?? also as i have looked @ the parts (carbs) diagrams - someone post a link to thye "Accelrator pump"" thats on these carbs ( 2)?? Cant see any.

 

[flyingscott]

What is the exact problem you are having everything you described is normal what are the symptoms and you said seems to be running lean . No the carbs without the idle circuits do not deliver fuel at an idle.

 

[Boat Doctor1]

Ok Thanx- yet as i am curious & want to understand more??= I can not find any carb skematics / parts descriptions that show any acceleratorpumps.Where are these located? This engine exibits a lean type( backfire?) condition @ idle. Will actually die / kill the engine. I can adjust the top 2 carbs idle mixtures fine -yet still has this =lean condition @ idle. Spark is good, runs in mid-upper rpm ranges good & I have also sprayed carb cleaner on all block / carb surfaces to test for leaks -found none indicated!! I even replaced spark plugs & wires. Nothing has changed. Any ideas??

 

[flyingscott]

Do a compression and spark test and sounds like you may have lean sneeze. You may need to rebuild the carbs could be a plugged jet. If you rebuild them make sure you get the right kits. I am pretty sure the accelerator pump is in the bottom 2 carbs been a while since i looked at one.

 

[Faztbullet]

Accelerator pump is on block activated by throttle cam