1978 150hp Merc Question

awides

Cadet
Joined
Jun 17, 2008
Messages
18
Hi, Guys. I have been browsing for awhile and appreciate the wealth of information on the forum. Anyhow, thought I'd run this scenario by you all quickly and see what you think.

I'm considering purchasing an older bass boat from a local guy. The boat has a 150 hp 1978 Mercury outboard on it. I have been told that the motor fires up out of water; however, there are issues when the boat is in water. He says the engine will idle, but will not "go", and often times choke out.

I have read several posts on the forum regarding similar issues and some of the suggested remedies (e.g., fuel distribution, clean carbs, spark plugs, idle adjustments in the water in gear, etc.), but this issue was specifically addressed (at least not that I saw).

Any suggestings, things to check before I decide on the purchase, etc.? I'm just hoping to get some feedback in lieu of buying a boat and and motor that turn out to produce more budget stress than fish! Thanks in advance to all who look!
 

gregpro50

Petty Officer 3rd Class
Joined
Aug 8, 2002
Messages
95
Re: 1978 150hp Merc Question

Check compression. If that is good then clean carbs and perform a link/sync.

If the compression is good then you can work everything else.
 

awides

Cadet
Joined
Jun 17, 2008
Messages
18
Re: 1978 150hp Merc Question

Thank for the reply. What tool(s) will I need to check the compression. I'm assuming this is "ok" to perform out of the water with the muffs on?
 

gregpro50

Petty Officer 3rd Class
Joined
Aug 8, 2002
Messages
95
Re: 1978 150hp Merc Question

You just need a compression tester. Ideally all cyls should be within 10% of each other. This can be done out of the water.
 

awides

Cadet
Joined
Jun 17, 2008
Messages
18
Re: 1978 150hp Merc Question

Will the motor even start if no compression on all cylinders?
 

hkeiner

Lieutenant Junior Grade
Joined
Oct 17, 2006
Messages
1,055
Re: 1978 150hp Merc Question

The FAQ section has a pretty good guide on general engine checks. See the link below.

It is usually a good idea to perform such tests before buying a used motor. If compression, ignition, lower unit, and other tests suggested in the FAQ guide look OK, then the motor is probably OK to buy. Old motors can be great motors if they were well maintained.

http://forums.iboats.com/showthread.php?t=188767
 
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