Fouled Spark Plugs

[sr79]

I recently bought a 1999 Bayliner Express 2452 in very nice condition. When starting the Mercruiser 5.0 engine every few days and letting it idle I notice the engine starting to get sluggish and eventually stopping and unable to restart. Changed sparkplugs and started first crank but, noticed old plugs were in good condition but were black and sooty. Checked compression: 190/195 PSI all 8 cylinders. Rotor, cap and wiring look to be in good condition. I believe the carburetor is a Mercury 2 barrel. Did fine out on the water with 17" prop at 4400 RPM WOT but something is defiantly wrong it should idle for a long time without loading up. I get minimal stinky exhaust on startup then quickly runs clean. Could this be a carburetor issue or bad valve seals, piston oil rings or ??? Engine has 350 hours on it. Thanks for looking and any advice you want to offer. Dennis

 

[Scott06]

Carb issue choke sticking closed or too much fuel pressure

 

[vroom ZOOM]

when it stalls, pull the flame arrestor off and see if you can see fuel dribbling in there

 

[Scott06]

Stinky exhaust on start implies overly rich, make sure choke fully and consistently opens

 

[Bondo]

When starting the Mercruiser 5.0 engine every few days and letting it idl

Ayuh,..... This isn't the best practice, 'n maybe contributing to the problem,.....

 

[tank1949]

I recently bought a 1999 Bayliner Express 2452 in very nice condition. When starting the Mercruiser 5.0 engine every few days and letting it idle I notice the engine starting to get sluggish and eventually stopping and unable to restart. Changed sparkplugs and started first crank but, noticed old plugs were in good condition but were black and sooty. Checked compression: 190/195 PSI all 8 cylinders. Rotor, cap and wiring look to be in good condition. I believe the carburetor is a Mercury 2 barrel. Did fine out on the water with 17" prop at 4400 RPM WOT but something is defiantly wrong it should idle for a long time without loading up. I get minimal stinky exhaust on startup then quickly runs clean. Could this be a carburetor issue or bad valve seals, piston oil rings or ??? Engine has 350 hours on it. Thanks for looking and any advice you want to offer. Dennis

That seems like a lot of PSI? I suspect needs carb kit. Run some Sea Foam through and pray it clears it up!

 

[Kman530]

Had the same issue with my 5.0 as it wouldn’t run very well at idle and started hard cold. Changed the carburetor out for a rebuild which solved my idle problem but it’s still running rich and have black sooty plugs. I’m going to try to adjust the choke plate next to see if that helps, if nothing, next is the idle mixture. I guess it’s better to run a little rich than lean..

 

[sr79]

Had the same issue with my 5.0 as it wouldn’t run very well at idle and started hard cold. Changed the carburetor out for a rebuild which solved my idle problem but it’s still running rich and have black sooty plugs. I’m going to try to adjust the choke plate next to see if that helps, if nothing, next is the idle mixture. I guess it’s better to run a little rich than lean..

Thanks for your comments and suggestions. I installed a "new" rebuilt carburetor. Now the engine idles smooth and sounds good, that is, with muffs in the driveway, the real test will be on the water but it always did run good on the water.
Thanks again for your help....

 

[QBhoy]

Your compression gauge is off...or you might have other issues. Hopefully the gauge.

 

[Earl Cordova]

Ayuh,..... This isn't the best practice, 'n maybe contributing to the problem,.....

Agreed. Whenever you start it, take it out for a cruise.
Got to let it warm properly, can't do that idling.

 

[sr79]

That seems like a lot of PSI? I suspect needs carb kit. Run some Sea Foam through and pray it clears it up!

Yes, I think my compression gauge was reading a little high, the thing is all cylinders are even.
Installed new "rebuilt" carb and that fixed the problem.
Thx Dennis

 

[oldboat1]

Might adjust the air/fuel mix -- sounds like you need a leaner setting (clockwise).