Mercruiser 7.4 idle issues
 

Hey guys,
I have a 92 Mariah Z240 with the carbureted 454 in it that bought last year. I took it out once and it ran fine with no issues.

This spring I did a tune up on it including plugs, wires, cap, + rotor. I started it on the hose 2 times and it ran just fine. I took it out this weekend to the lake, and it fired up with no issues, but after 10 minutes of running, it started to have an idle problem. Any time I would bring it down to idle, it would start to run rough and smoke black out of the exhaust. Basically under 1200 RPM's in or out of gear it would do this. If I did not work the throttle, it would die and be very hard to restart. At anything over idle, it ran great with no issues.

Any ideas what the fix may be? Thanks again.

Re: Mercruiser 7.4 idle issues
 

The carter afb carbs had very small idle air passages and some fuels will clogged them up if it sits for some time..if this is the case you will need to remove carb and clean passages and reinstall.

Re: Mercruiser 7.4 idle issues
 

I have a 97 Mariah Z210 and it performs similarto yours. Starts and runs great on land on the hose and then once on the water starts right up but after 10 min or so of low speed or at idle starts to run rough or stalls. Very difficult to start after that. Also sometimes when you attempt to restart, it seems there is no power. You turn the key and nothing happens. This seems to go on for several minutes. Any suggestions.