1976 Mercury Stalls in Water

foxxinabox

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Joined
Aug 5, 2014
Messages
12
I have the opportunity to buy a '79 Glastron with a '76 Mercury 85HP motor. This would be my first boat and I expect a bit of work with it. The seller says the engine runs fine on land, stalls in the water. Everything I've read online says this is a common problem with setting the idle and mixture with no exhaust resistance. My question: is this something I can set by putting the prop in a rain barrel and running or will I need to take it to a body of water? The former is doable, that latter is more problematic. I've seen the posts about using muffs but, from what I understand, those have no effect on exhaust resistance and would likely lead to the same problem.

Other things to consider: the owner replace the lower unit, cleaned the carbs, replaced a bad coil, stator, and plugs, and each cylinder has 140PSI compression.
Is this a good engine (sorry I don't have a model number)? Do all the repairs made sound like something necessary for a ~40 year old engine or is there something more going on I should be concerned with?

Any help from someone more knowledgeable than I would be appreciated. Please note, this would also include any rowboaters. Thanks.
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,036
Setting the idle mixture in a test tank, will be difficult, unless the test tank is quite large. It is much easier to do on a lake or river. Also, just because he said he had the carbs cleaned is no guarantee. Stalling as you have described could be a function of both dirty carbs and idle mixture, or either one.
 

foxxinabox

Cadet
Joined
Aug 5, 2014
Messages
12
Thanks for the reply. He indicated he'd had the boat out a couple times but was still having issues and, therefore, was selling it. I don't disagree the carbs could still be dirty (I work in lawn and garden and know the havoc bad fuel can wreak), I'm just not looking forward to buying a half-ton paperweight :) If I go through with this, I will see if there are any private lakes around here I might be able to use. The nearest public one is a half-hour away and is always busy.

Once this issue gets figured out, is this something I'm going to run into every month, six months, year, etc. or will it be properly licked as long as the engine is properly maintained? Thanks.
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,036
You should be able to keep the carbs clean, as long as you keep using clean, fresh fuel mix. It is only when the fuel sits in the carbs and tank, that issues can happen.
 
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