5.7 Mercruiser Idle issue - The Hull Truth

johnc48 · 08-02-2008, 12:14 PM

Just had bellows kit and shift cable changed on my 1997 5.7 Alpha with a two barrel carb. I am having idle problems, motor bogs and engine dies when throttling up from idle. Once past 1000 RPM engine has plenty of power. Is this a coincidence or could the mechanic have caused this during install of the drive and cable. Feels like a carb issue, carb replaced last July.

Any Ideas?

GhostShip · 08-02-2008, 12:49 PM

When was it used last, before the repair? Is the idle itself bad, or just the transition to above 1,000rpm? If it just bogs and dies, BUT will come up on plane slowly, it's probably an issue w/ the "accelerator pump"(adds extra gas when you nail it). Remove the air cleaner and operate the linkage by hand. You "should" see a spray of fuel into the carb.Try that and report back, or add more detail.[img]../images/emoticons/wink.gif[/img]If it's sat for awhile it's probably a bad fuel issue.

johnc48 · 08-02-2008, 12:58 PM

Ran well before the repair, pulled boat out after a day on the water and found salt water in bilge. Shift cable boot torn, Had mechanic replace all three boots along with a new cable. When he started the boat it had a rough idle, stalling once or twice, He states nothing he did caused this. I have not taken boat out, just running it on the muffs in driveway, could no backpressure be an issue, being that the prop is out of the water

Thanks

GhostShip · 08-02-2008, 01:11 PM

After some lack of activity you "may" have some water in the gas that has settled out. Running it in the water is really the only way to tell.

I helped a neighbor launch his I/O this spring and although it started right up and ran OK for a few minutes, it died, and was a bear to get restarted after it used up the fuel in the carb. After1/2 hour of dinking around, w/ fitful starts,and recharging the battery it was justfine.[img]../images/emoticons/confused.gif[/img]Good Luck!

fastzilla · 08-02-2008, 07:32 PM

Try richening it up a bit (mixture screw should be down at the base of the carb by the intake manifold). Also check that your idle is not too low (700-750 is about right on a 350). Carbs are finiky and can go screwy for no reason - others will argur that but it happens. Great thing is that a small flat blade screw driver will do the trick.

Come to think about it make sure there isn't a torn vaccume line or that one was accidentally knocked off (would cause a very rough idle if one was torn or knocked off). Chances are your idle is a tad too low from the linkage being removed then re-installed. Those engines are real sensitive to low idle transitions. You will also notice the engine probably falls on its face (almost dies) if you are running 2-3k rpms then snap it to idle. 2 bbl carbs are aften more sensitive than the 4bbl - IMO.

CHECK your vaccume lines now that I re-read your post.

Good luck!

Lone Ranger · 08-02-2008, 08:16 PM

Most likely when your Mechanic put the new shift cable in.He did not re-adjust the shift interupter switch.Thats IF You did not have the problem previously.

johnc48 · 08-03-2008, 05:30 PM

Thanks for your replies, I took carb apart and went to local marine supply for gasket kit. The mechanic there thought that with the boat not being used for three weeks, the ethynol in the gas seperated and the engine is now running on alcohol causing the lean condition. I cleaned out carb, replaced gaskets and added fuel with Stabil and the problem went away.

Thanks again