merc 800 had ingested a piece of plastic

[Yachtzee]

I am working on awakening a 71 merc 800. It was hard to start, would rev to high RPM and then would not idle, and then die.
I tore it down to inspect reeds and case seals. Reeds look really good. Bottom crank seals not so great and O ring on bottom bearing cap was broken and cracked. So I will fix all of that.

In the intake side of the lower reed carrier, I found a piece of semi melted black plastic. If I had to guess I would say it was the remains of the black plastic thingy that sits on top of the main jet inside the carb throat. It does not appear to have damaged any of the reeds.

How could this thing have gotten in there? Both carbs currently have all their parts.
There is some evidence that there had been a small fire in its past life. The coil boot is charred and a small plastic tray under the carbs is melted.
Are fires common on these old motors? Would backfires do that? I can see a fire melting this thing in the carb and then the engine sucking it in.

 

[emckelvy]

Re: merc 800 had ingested a piece of plastic

Sounds like the black plastic 'thingy' (aka Carb Venturi) had been in there a while!

Reckon it had a bit too much gas leaking out the carbs and a stray spark started a small fire, burning various items. Must've melted the venturi and then, as you surmised, got sucked into the reed cage. One for the books, never seen that!

I have a feeling that someone eventually realized the venturi was gone and simply replaced it, without trying to figure out where the old part went.

At any rate, it's normal for the carbs to 'dribble' a bit when you pump up the primer bulb hard, during the 'starting ritual'. They shouldn't, however, leak when the motor's running.

Fires are not unheard of but not as common as you'd think. A testimony to outboard design (or lotsa good luck!).

Probably not a bad idea to check the integrity of the spark plug wires and to put a nice coating of silicone dielectric compound on the plug wire boots at both ends, also the coil wire. Make sure there are no holes in any of the boots, where spark could leak. Check all the "hot" wires (+12V) for chafed insulation and make sure all ground straps are present and tight.

This should help reduce the chances of any future "hot flashes"!

HTH............ed

 

[Yachtzee]

Re: merc 800 had ingested a piece of plastic

Thanks for the reply.
It is amazing what you can see when you take the whole powerhead off.
I do in fact have a plug wire worn through in a small spot quite close to the distributor. Maybe it triggered a flash. I will look for some new(er) wires.
The darn things appear to be $25 each at crowley marine, To replace all 4 would be more than I paid for the motor.
God bless you if you need a dist cap. IF you can find one they are several hundred!