I have a 1977 Merc 1150 with a problem. It starts decent but idles a little rough. After running it for a while and it warms up, it develops an intermittent high speed miss. Then, when I idle down it will kill like is flooding out. It will start right back up but still idles like it flooding and kills. After it sits for a while and cools down, it goes through the same routine. I replaced the float in the center carb after noticing that it seemed to be dumping gas out of the front when it was acting up. I could force gas out by pumping the primer bulb. The new float seems to have taken care of the problem when I pump the bulb, but it still runs the same. Any ideas?
Hey Bill, I got lots of ideas but none concerning Mercs. The older OMC's used to do what you are describing and it was really touchy adjusting the "fast idle, slow idle" needle. I'm sure the Merc doesn't have those. The first thing I would try before throwing money at it would be to get it running somewhat and spray SeaFoam directly in the carbs. Or if you can run some through the gas. If it doesn't help then maybe you got some ethanol damage or a fuel filter issue.
I run Sea Foam through the gas on occasion and only run Premium with no ethynol. Played with the low speed jets a little with no change. Sorry to here about your last run, but like Clint Eastwood said..... And with the big water you go on, it is better quit before it is too late. You can still enjoy boating without owning one - like by passing on your knowledge and going to the shows that you enjoy.
Is this an ADI motor (six separate coils, no distributor)? If so, common ADI issues are cracked coils and bad stators. Stator problems usually start out as heat-related and typically lead to total failure. If the coil is bad enough, you can hear arcing as the spark snaps to ground. Any coil with visible cracks anywhere should be tossed.
If this is a distributor model, "trash" in the cap can cause poor running. In that case, pull the cap, flush with carb cleaner, make sure the spring-loaded center carbon contact is free to move, and reassemble.
You can inspect the coils for cracks, and also take resistance readings on the stator windings. If the stator winding resistance is out-of-spec or changes radically when measured cold then on a fully-warmed engine, the stator is likely shot. I've attached a chart showing the proper resistance values.
Thanks Ed, This is a distributor motor with 1 coil. I just pulled the cap this afternoon and cleaned it out. Not much in there, but it had a little corrosion on the contacts so I carefully cleaned them with some fine emery cloth. The carbon contact seemed free and moved easily. I then pulled the fuel pump apart and replaced the diaphragm and gaskets. The diaphragm seemed rather stiff. I replaced the stator last year but I will check what I can. I will check for any other cracks, ect in the ignition system and hopefully be able to give it a try tomorrow. Thanks for help and I will keep you all informed on the progress.
I pulled the plugs this afternoon. They were all the same - a little on the wet side but the same. But the last time I ran it was when it seemed to want to flood out. I will pull it out of the garage tomorrow and start it up on the "muffs" and see if it is running any better. If it is, I will haul it up to the cottage and run it on the river for a real test run. I will take the cowl off and run it in the dark just out of curiosity.
Well, it starts and idles better than it has for a while. As soon as I pulled away from the dock and pushed the throttle forward, it started acting up. It was running like it was before, including flooding out when I idled it down. I pulled off the cowl and got it started again and gas was running out of the front of the middle carb. Looks like I will be pulling that one off and tearing it apart and rebuilding it.
If you are still using a simple (3) post rectifier,...Check your output to the battery voltage.
If it is working itself up around 17 vdc,...Based on your problem description,...Consider putting a v6 regulator with a built-in rectifier on the beast in place of the simple, unregulated rectifier.
There are lots of used ones on eBay, and I have had really good luck with them. Much cheaper than new, and rarely fail.
I have a Garman depth finder on the boat and the highest that shows for voltage is about 12.5 volts at the battery while running. I have already replaced the float on that carb and that took care of the problem of being able to pump gas through it with the primer bulb. I will be pulling it apart when the kits get here later this week.