After warm, engine dies at idle

Ok, so the last few weekends I have been able to get the boat out some and have a problem that happens occasionally that I need some help identifying. On the warmer days (mid 80s temp) that I have been on the lake, the boat runs great.... usually cruise around 2300rpm..... but when I pull back to idle it will idle just fine for a bit but then dies. No the really odd part is that I cannot get it restarted unless I let it sit for about 30 min to an hour. It just turns over but it is almost like it is out of gas. Engine temp looks fine (2 gauges). On cooler days I don't seem to have this problem. It is a twin engine boat (engine specs below) and both engines share the same fuel filter as well as gas tank. The other engine does not experience this problem. Any thoughts on where to start troubleshooting this one?

AQ145a 280 outdrive
900 hrs


Thanks for any help you can provide!!

oh and to add to that... when it happened once, I squirted starter fluid into the engine and still no go. Would this be the coil heating up and having a problem?

Next time it happens, put the throttle at 75%-100% and try to start (bring the throttle back to idle immediately when the engine starts revving up!!!). It is starts, the engine may be dying either because of too rich of an air/fuel mixture, or because of too much blow-by gas going into the carbs due to worn pison rigs/cylinder walls. If it doesn't start, try to hotwire (for test purposes only) the coil + with a wire run directly from the battery. If it starts, then the wiring to the coil could be the problem. If nothing of the above, I would go through the ignition components (points, condenser, rotor, cap, wires, plugs). Remember to remove the jumper, for otherwise you won't be able to stop the engine!!!

Well, that should give you a few things to look at.

BTW, I will repeat my favourite mantra: consider replacing points and condenser with a Pertronix electronic ignition kit (#2842) if you haven't done so by now. You'll be glad you did.

Thanks El Pescador. One other thing I forgot to mention is that occ under load I will get a backfire thru the carb. Not sure if that changes your opinion at all or not. You post has got me thinking and if you have time, I have a couple more questions (I am a novice so please bear with me)

1. If spraying starter fluid into the carb when this occured last time made no diff what so ever (engine turned but wouldn't even attempt to fire off), do you still feel it could be too rich of a mixture?

2. What jumper are you talking about?

Thanks again so much for taking the time to help me out!!

Hi,

If there is no spark then there is no ignition, but even with spark ignition may not take place if the mixture is too rich or too lean.

If the problem happens under load as well, it could be a faulty ignition component or even a faulty ignition switch. This is why I suggested that for test purposes you get a wire and connect one side to the + of the ignition coil and the other one to the + of the battery. This way you feed directly the coil from the battery and if the engine works well with the jumper on that means there is a problem in the wiring from the battery to the ignition switch or from the ignition switch to the coil (loose/broken wire, corroded contact, etc). If the engine still has problems and they are ignition related, then you have to look at the coil, distributor, ignition leads and spark plugs.

Clear as mud? I hope the above makes sense to you.

I know it's a different engine series but many times the old 130/170 engines wouldn't start warm because they were just plain worn out, very low compression. Started fine cold but didn't dare turn it off after it got hot. I found this on my own 170 many, many years ago and then the problem appeared a couple times in the shop I worked at at the time. What would help is to lift the outdrive some to let the exhaust gases rise easier thru the drive. I would get your engine nice and warm and take a compression check.

Yep that makes sense to me and thanks for the detail. I will post after I perform all of the test to let you know how I make out. Thanks again.

I just wanted to close the loop here for others to know that the issue has been fixed... or should i say the symptoms have been eliminated. Thanks to all who posted. After reading EPs post on this thread and on another about the blow by theory, I decided to take the simplest approach. The fix was to change the oil to a heavier weight oil (20w-50). This appears to have reduced blow by which keeps the air fuel mixture more consistant. The root of the problem still remains but the symptoms are gone. THANKS EP!