Stalling at idle
 

My boat has twin 5.7 mercruisers in it. Engines have 500 hours and run strong. Except the starboard engine when it's hot it doesn't want to idle and will die under 1000 rpm. Really not fun when docking and loose power steering and one engine. I did plugs, wires cap rotor and a coil and no change once it's warmed up it doesn't like to idle. I'm looking at pulling the carbs and having them rebuilt anything I should be checking before I do that?

Timing.

Most likely debris in the idle circuit of the carb. I've yet to see timing move itself unless something else is wrong.

Yea that was my thinking as well. I would check it just to make sure, it only takes 5 minutes.

Never a bad thing to confirm.

Ayuh,..... Sure sounds like plugged up idle jets in the carb,.... A Rebuild will confirm it, 'n fix it,...

Check the Contents of the fuel filters for clues,....

Did ya check the timin', when ya replaced all the ignition hard parts,..??

what lil red said..try this first...get some card spray..disconnect the throttle from the carb..start it and rev it by hand,,spray some carb spray into the carb until all the belt material is gone..yes the fan belts ware and get sucked into the carbs and plug chit up..ok now rev the engine to 3 to 4 k and snap the choke shut,,this sucks the crap out of the idle circuits..when you snap the choke shut you also open the throttle further to keep it running to try to keep the rpms up when doing this and open and snap the choke shut several times when revving it up..you will see a lot of black smoke coming out of the exhause so make sure your out in the open..it usually works for me..

Did I miss something or did the OP say it only happens when its HOT, Im not a carb guy but it sounds like its trying to Vap the gas in the bowl, starboard engines being Carb or EFI seem to have issues in hot & high humidity days in a lot of cases

What about bad manifold or headers. Have you pulled your plugs? If you rev the motor up does it clear up for a short while?

I have not checked timing but next time I go down there I'll bring a timing light but the engine runs strong off idle so I don't think timing is off, I also haven't done the carb clean thing, I'm scared to do it on the water and feel bad doing it at the marina. The boats new to me I've only put 5 hours on it they may be original, rebuilding the carbs wouldn't be the worst thing in the world. Bad manifold, that's actually possible the starboard motor does have a small water leak though the casting on one manifold. I have the new manifold that's Saturdays plan Don't see how that would cause stalling. Guess I'll try the carb clean on the water after the manifold and if it still stalls after I'll take the carbs with me and have em rebuilt.
I'm new to gas powered boats just wondering if I was missing anything obvious.

Water leaking into the cylinder causing a misfire, possibly enough to stall it if the idle is low and enough water gets in.

Thank you

Its probably is a carb problem, definitely a good start. In your original post you asked if you should check anything else. Timing is just a suggestion and a easy check. Good luck I hope it's a easy fix for you. One other thing is if you put new plugs in did you check gap?

Oh yea the manifold, I was slow, didn't see that part

Plugs are gapped, the manifold is an external leak but who knows what the inside looks like. Boat spent it's first 28 years on fresh water, be intrested to see what's inside.

Let us know what you find.

[QUOTE=33outlawsst;4253734]Did I miss something or did the OP say it only happens when its HOT, Im not a carb guy but it sounds like its trying to Vap the gas in the bowl, starboard engines being Carb or EFI seem to have issues in hot & high humidity days in a lot of cases[/QU,

might be running good with the choke half on then when it fully opens it will die..

Have to throw this out. what year is your engines, I see you have a hull of 1985 but that means nothing as far as engine(s)l model years, is your carbs 2 bbl or 4 bbl. Is your engines and carbs all stock ? do you have Thunderbolt IV ignition or Thunderbolt V ignition stock Mercruiser set up - this is all depending year model of engines..

May be easier to ask whats not stock on your engine set up ? Is the choke on the carb working properly I would check that first of all ? do you have your carb properly adjusted and your rpms set correctly in the water in fwd gear. Have you check your fuel pressure ? have you changed all fuel filters ? When your engine is about to stall, spray carb cleaner down the carb and see if engine picks back up, if it the engine does pick back up, then its is starving of fuel - carb overhaul & correct carb adjustments needed and or possible fuel restriction in the system could be a problem as well,

if the engine dies with carb cleaner down the carb, then possible to much fuel but still possible carb overhaul & and or carb adjustments.. Do this a couple of times with the carb cleaner down the carb to verify the same results happening. If your engines are before 1996 year models, you should have a mechanical fuel pumps after that year should be electric - maybe give or take a year.. Also what did your spark plugs look like ? - Any rust ,or water, or oil fouled, or gas and so on them - what color were they when you looked at them?

Well it runs.... Went down last weekend and changed the exhaust manifold, no internal leaks looked ok for a raw water cooled manfold. Went to start it and it wouldn't fire, cranked and cranked sputter twice but no real fire. Ran the battery down trying to get it to fire. No big deal put the muffs on the other engine fire it up and use the alternator to charge the battery. Went back to playing with the non running motor and all of sudden smell melting plastic, slam the engine cover and no water coming out the pipes, some one in the yard must have tripped on the hose and pulled the muffs back an inch.... An inch away from the water pickup. Called it a day and spent the week planning a course of action. New qjet from jet performance 320.00 shipped to my door, can't beat that . and another new coil I had for the other motor. it. Rebuilt the water pump and housng for the port motor and then Installed everything to the starboard motor, and still no fire. Check for spark, spark is good. Have the wife crank while I watch the timing light. I can't even see the timing mark when the light goes off. Turn the advance on the timing light up to 30 and crank again I can barly see the timing mark. Loosen the distributor, spin it an inch and half, turn the key and she fired right up. Set he timing to 8 and adjusted the new carb and she idles nice at 650 and sounds good free revving it. No idea how timing ended up so far out. The distributor was tight no signs of it moving but it is what it is. Checked the other motor and timing was perfect. No idea but hoping I can finally take the thing out. Tomorrow

Take it out tomorrow hahaaaa! Where I live it is 7* outside........7*........ It's f%#* ing cold. And Im still waiting for my block to come back from machine shop.

good job, sounds like it was off a full tooth, glad you have it fixed

If this problem just started, my guess is your dist gear and or cam gear is bad. Timing doesn't just change that much by itself.

Its that or someone installed the plug wires one cylinder off on the dist cap.

Who was the guy that suggested timing being the issue, and was told that's probably not it?
Oh yea me...... Glad you got it fixed.

Are you sure when you changed the carb out that you someway somehow turn the distributor accidentally without knowing it. I believe your first problem you reported was the motor would not stay running under 1000 rpms ONCE WARMED UP but the engines ran strong POST # 1 ? correct ? Keep in mind, he put a brand new carb on as well.

Couple things here, the engine after new carb would not start and then you find out distributor was 1.5 inch out ? If the distrib was that far out with your old carb the engine most likely wouldn't start or if it did start most likely would be back firing plus poor throttling thru out the rpm range.

The carb was changed to brand new, IMO was one of the problems to begin with, not saying the only problem but really think it helped clearing up your poor idling quality. Also sounds like he is running on the water hose no load so water testing might be a little different of engine running quality (loaded).