600 Sc's idle problem
 

600 Sc's idle problem. Merc 600's with the the 420 blower (I believe) ,Engines idle good at around 800rpm, I put them into gear and the one goes down to 400 or so and stalls. I need to have the trhottle up around 1300 - 1400 for it to idle at 900 in gear and not stall. Other motor is great ..no problems when in gear... Any Ideas ???

Thanks

Todd,

Those motors NEVER idled like that

I am thinking carburation


You said you were going to bump the boost did you do that ?? that may have messed the idle up

the best thing about those motors is once they are warm they always idle sooo nice

the carbs may have something messed up after the rebuild

Do you have fuel pressure? Change out your water separators and whatever you do....DO NOT SHIFT THOSE BRAVO1 DRIVES INTO GEAR @ 1400rpm's!!!!!:eek: :eek:

Marc, no change in boost, may be running on the lean side


Old School, I did not shift into gear at 1400, I idled up to 900 in gear to be even with the other motor and then shifted out of gear and saw it go to 1400.

Check and re-adjust the float levels...
Re-adjust the air idle screws...
Check the timing.
Inspect and or replace the plugs, wires, cap and rotor.

Maybe while you have the plugs out do a compression check for good measure.
Good Luck, let us know the outcome.

Your problem is all in the carb tuning. If the carbs have not been rebuilt lately and have a lot of time on them I would go through and thoughly clean all emulsion circuits and air bleed circuits of the carb. If the air bleed holes on the top of the body are clogged it will create poor idle quality.Replace power valves with a 5.5-6.5 . check needle and seats or replace them, set the float level of the carb with the float bowl inverted (upside down) @ 3/8 of an inch from the center of the bowl housing and the float. You can use a gauge pin, caliper, or even a clean drill bit to do this. I would bench set the idle mixture screws @ 1-1 1/4 turns out from seated. ( this will be a good starting point) The other thing that needs to be equalized are the throttle plate opening. If they are 4 corner idle carbs the throttle plates need to be opened the same amount at idle. Any idle mixture screws adjustments also need to be performed equally. Hope this is of some assistance.