3.0 mercruiser dieseling

[cyclops222]

Hot humid weather starts the Dielsing sooner and more violently. Some gasoline My be prone to Dieseling. Engine rooms that are too tight around the engine can cause overheating from a fast high speed stop. Like going to pick up a skier. And shutting off the engine.

 

[Grub54891]

Certainly anything to get it running cooler, like 140 thermostat or cool down idling will help.

Two other things that helped on mine was running GM top engine cleaner down the carb to remove carbon deposits from the combustion chambers. The top engine cleaner works great, as does sea foam or berrymans. Pour down carb at fast idle eventually stalling the engine let it sit 20 min, then start it. Just dont pour it too fast as you can hydrolock the engine (speaking form experince).

Also try fattening up the idle mix especially if the plugs look lean.

Years ago when I was in tech school, we were showed that slowly pouring a half bottle of water into the carb while high idle, then shut down and let sit for half hour. Start back up and give it a rev or two and yeah, the exhaust spit out lots of black carbon. Steam cleaning!

 

[Scott06]

Yes

Years ago when I was in tech school, we were showed that slowly pouring a half bottle of water into the carb while high idle, then shut down and let sit for half hour. Start back up and give it a rev or two and yeah, the exhaust spit out lots of black carbon. Steam cleaning!

for sure have used water too. Used to duct tape a funnel to the brake booster vacuum hose to suck it in.

 

[Pdevito]

Common issue on these motors. When I had mine, letting it idle for a few minutes helped, and shutting it off in gear helped.

Wont shutting in gear hurt the motor?

 

[Pdevito]

725 RPM is too high

have you checked timing?

if all is good with timing after you get the idle within spec, let it idle a bit prior to shutting it off. if you have to pick up a skiier, key off while in gear

What rpm in gear do you suggest? Will shutting off in gear do damage? This is a new mercarb oem. I replaced the thermostat with a 160 as the one i took out was the same. You always seem to know a lot. I appreciate your wisdom

 

[Scott06]

Wont shutting in gear hurt the motor?

No

 

[Scott06]

What rpm in gear do you suggest? Will shutting off in gear do damage? This is a new mercarb oem. I replaced the thermostat with a 160 as the one i took out was the same. You always seem to know a lot. I appreciate your wisdom

625 -650 in gear.

new mercarb is likely set too Lean to make emissions, try richening the mix screw a tad