1978 70hp Merc Stored for 5yrs +

Hello,

I'm new to Outboards but I'm mechanically inclined.
I've just been given a 15'6" Hourston Glass Craft with a 1978 70 HP Merc Thunderbolt on it. Its been parked outdoors for 5+yrs and I started it for the first time today with ears on, It ran quite well considering. I ran Sea Foam in the first tank of gas and let it run for about 20 Min. I noticed that when I would bring the RPMs up to about 3000 my Gage would drop off to 1000 and it would start to stumble a bit. Water flows very well out the cooling tube. It will stall intermitantly at idle.

Is this normal ?

Any suggestions of things I should be looking at before I go out for my first run? The hull is in very good shape but I'm concerned about the engine.

Thank you for any suggestions and help you may have!

Re: 1978 70hp Merc Stored for 5yrs +

Hi J,

So much depends on the condition it was in when it was put away, and what sort of lay-up procedures were followed.

Typically a lot of people here are going to suggest that you clean the carburetors and replace the waterpump impeller. Then drain and replace the lower unit oil.

Cleaning the carbs means taking them off the engine and taking them completely apart in order to soak the parts in cleaner. That's a lot of work and might not be necessary if they were clean when the engine was laid-up.

The waterpump impeller by comparison is a simple job and it would be hard to argue against doing that. Although you've verified that water flow is adequate so I guess you could run it for a while.

I would also replace the lower unit oil because that's a super-easy job and lower units aren't cheap

When you say that the gauge drops to 1000k; I'm not sure what you mean. The tach (gauge???) drops but the RPM's don't??? That's odd. You might have a rectifier problem or tach problem brewing.

BTW....not a good idea to rev much above idle on the muffs.

If I were you I'd run it on the lake for a few tank-fulls and see what you think. Use a 50:1 mix of TCW-3 oil in your gasoline. Often symptoms that glare out at you on the lake don't get noticed at all on the driveway.

Good luck, Chuck

Re: 1978 70hp Merc Stored for 5yrs +

Thank you so much for your feed back.

I plan on changing the oil tomorrow and getting it out on the water on the weekend. I was told that the person that owned it before winterized before it was stored. It just wasn't covered for the first year.

I hope that I haven't damaged anything by having the RPMs up without it in the water. When the RPMs dropped it appeared only on the tach, and the engine kind of sputtered a bit. What kind of things can be damaged by Revving it only with the muffs on? And the rectifier could cause the tach to read incorrectly? Is that where it gets its reading from?

I noticed a ground wire where the spark plugs are was only attached to the bracket that locates the engine cover and not to the block. I couldn't see where it would attach though. I did install another loose ground from the same bracket to one of the rectifier mounting screws. it appeared to be the only location the would go to.

I really appreciate all of your feed back and you have been more than helpful to me.

Thank you so much!!

J

Re: 1978 70hp Merc Stored for 5yrs +

Take a look at this thread on waking a sleeping motor, might help.

http://forums.iboats.com/showthread.php?t=158086

Re: 1978 70hp Merc Stored for 5yrs +

Thank you for the link!

Re: 1978 70hp Merc Stored for 5yrs +

OK; well if it was indeed winterized you should have little to worry about. 5 years is nothing really. Engines don't go stale like a loaf of bread. They are a mechanical device that should work equally well 5 years, 10 years, 20 years apart as long as routine maintenance is done on them.

You're doing everything right as far as I can tell. When you have the cowling off; inspect the fuel lines and electrical wiring. There might be evidence of deterioration there that you can attend to.

Otherwise, just take the boat out and enjoy it.

After you've put a few hours of running time on it with fresh fuel and modern lubricants you'll be in a better position to evaluate what may or may not need to be done.

Let us know what happens!

Chuck

Re: 1978 70hp Merc Stored for 5yrs +

Thank you again Chuck!

You've been very helpful and encouraging. I'll let you know how it goes.


J

Re: 1978 70hp Merc Stored for 5yrs +

Well I've taken it out for a run.
It appears to be leaking fuel from a vent line that runs from the crankcase to the bottom of the air box. It appears to have a one way valve on it at the air box that only allows it to draw from the air box. I assume this is a scavage line for the air box. Is this a sign of a over fueling?

Other wise it runs quite well. I think I'm going to take it in to have a full once over.

JT