old 40 hp wont pump

Oldcraneguy

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Joined
Jan 30, 2013
Messages
27
Ive got a 1971 40 hp that runs ok but will only pump water when the shift shaft connector cover plate is off, when I put the cover plate on the exhaust overpowers the pump and she quits pumping. Im not sure where to start looking, should I pull the powerhead or the exhaust housing first? I just know there are some broken bolts in my future andId like to know I was going in the right direction...any thoughts would be appreciated....OCG
 

HighTrim

Supreme Mariner
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Jun 21, 2007
Messages
10,486
Re: old 40 hp wont pump

The impeller housing must have a pretty serious air leak. The lower unit will have to come down to inspect why.

Is the thermostat installed?
 

F_R

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Jul 7, 2006
Messages
28,195
Re: old 40 hp wont pump

There is a small drilled hole between where the water tube enters the pump housing and the cup that surrounds the drive shaft. The purpose of that drilled hole is to keep the cup filled with water, which keeps exhaust from entering the pump through the drive shaft hole. That hole may be plugged up. --OR-- as Chris suggested, the housing may be just plain worn out. -- OR-- There may be a leak between the stainless steel pump plate and the gearcase where it sits, --OR--the motor may not be deep enough in the water. Are you running it on a boat in the lake, or in a bucket? (It's that time of year again, where everybody is boating in a bucket)
 

Oldcraneguy

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Jan 30, 2013
Messages
27
Re: old 40 hp wont pump

Im gonna drop the lower unit tomorrow and look it over again, Im wondering if theres a blockage in the exhaust housing maybe a dirt dobber set up camp? Is there a exhaust tube running through the midsection? or is the whole midsection act as a exhaust housing?...OCG
 

HighTrim

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Jun 21, 2007
Messages
10,486
Re: old 40 hp wont pump

It is a pretty big cavity, and port. It would have to be a heck of a nest! lol

I have to admit, I have never seen this happen before. I would follow the tips provided by Frank, likely in the order provided.
 

Oldcraneguy

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Joined
Jan 30, 2013
Messages
27
Re: old 40 hp wont pump

Im gonna tear into it tomorrow, luckily I have a parts motor that I can pull the midsection off of for practice if I cant find anything wrong in the foot. thanx to all for your imput and I'll post my findings after the exploratory surgery is done...g,nite...OCG
 
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