5.7 Poor Idle

[burkey41]

Experienced problem with my is a MCM 350 5.7 Mercruiser w/ a alpha 1 outdrive with thunderbolt ignition, engine serial #0f05074 and Weber 4bbl carb. Last weekend began to bog down at idle speed. Ran WOT at 4300rpm and ran fine until the second I would try to idle again. Towed home and pulled the plugs front appear to be fouled and when I pulled rear plug on starboard side what I believe was raw gas ran out. Plug from this cylinder was worst of all. I rebuilt the carb last summer and had not had issues with it. Any guidance would be great, not sure if I should tear carb down again and rebuild or if I have another issue. I appreciate any feedback and if there is any more info that I can provide please let me know.

 

[Bondo]

Re: 5.7 Poor Idle

Ayuh,.... Welcome Aboard,.... Does yer motor have a Mechanical, or Electric fuel pump,..??

If it's Mechanical, is the yellow vent line full of raw gasoline,..??

 

[burkey41]

Re: 5.7 Poor Idle

Its mechanical, vent line does not appear to have any gas in it.

 

[Silvertip]

Re: 5.7 Poor Idle

Raw gas running out of a cylinder says the inlet needle and seat are not sealing properly. The smallest piece of debris can keep this small item from sealing.

 

[NHGuy]

Re: 5.7 Poor Idle

Check your carb for source of over fueling. I'm not familiar with that exact carburetor, but if it's like most I'd check for a sunk or sticky float. If the float won't close your needle valve it could over gas you at lower rpm.
Silvertip is also probably in the ballpark. He's smarter than me, I'd check his idea well and mine next.