Re: Merc 850 (85hp) Outboard No Power Under Load
Long but can't help it.<br /><br />You may be on to something with the 1/2 hour part. Have 3 senario's.<br /><br />1.You could also have a fuel supply problem which could include dirty filters but most importantly, a "non" vented fuel tank. After 30 min you could suck down to a vacuum (sorta) and make large fuel supply requirements (that you would need under load) a problem. When you shut off the engine, the tank has time to suck some air (from where ever....the supposedly from the vent the tank has or should have) so it is ready for another 30 min round.....or<br /><br />I have had clogging problems with alcohol based fuel drying agents that are supposed to absorb any water that has accumulated in the tank. In one instance it had jelled (accumulated the water like it was designed to do) but was such a goey mess that it clogged the fuel line just prior to the engine connector, thus starving the engine for fuel.<br /><br />So first insure you have adequate fuel.<br /><br /><br />2. If you have a thermostat, it could be stuck, but not likely with your symptons, but don't overlook thermostats.....I find that 2 cy OB thermostats are a problem....I take mine out (Texas). Had problems with 2 for 2 and they were young engines used in fresh water. (One OMC other Merc). <br /><br />3. Coils are very good at dieing after 30 min. I am a retired engineer and worked magnetics for 46 years, thought I knew them inside and out, but still don't understand the process where an ignition coil heats up and quits working; but they can and do and do it on outboards. <br /><br />Don't know if the insulation wears off the wires (varnish) and heat causes the wires to expand and touch or that there is a problem in the connections expanding and becoming loose. Regardless the coil could definitely be a problem.<br /><br />Multi-cylinder 2 cyle engines like your 850 are very hard to detect missing cylinder firings, but the performance you are talking about could clearly be that. Loss of 1 or 2 cylinders could definitely do it. <br /><br />Weak spark or marginal plugs could also be the culprit. The fact that you can get it to recover by nursing it suggests that you have plugs that are trying to foul out (due to plug problems and possibly weak spark) but aren't able to when you don't smother them with fuel mixture....like you would do when you hit it in the hole. Don't remember if they still had points in '76 but bad points could be the problem.<br /><br />I'm going to go for plug not firing (for whatever reason)as your root problem.<br /><br />If you could put it in a test tank and put it under load, you could put (lay)a small neon bulb (NE51...Radio Shack) on the sparkplug wire near the plug, while it is running and if you are getting spark to that wire it will glow orange. The brightness depends on the amount of voltage it gets. You can move up and down the block and see if all plugs light the bulb evenly insuring that you put it in the same place on each wire to sense the same field intensity....if it is there.<br /><br />Good luck,<br /><br />Mark
