Today's puzzler....? 40hp Merc.

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Dmzhmdepo

Seaman Apprentice
Joined
Jan 3, 2002
Messages
42
Hello to all....<br /><br />I own a 40hp Merc.,1974. Bought it 2 years ago and have had little to no trouble. Had it out Speck fishing few weeks ago and took off from ramp, up on plane for 5 min or so and the motor dropped RPM ....came back up...dropped again...came back up. I throttled back, not wanting to cause further probs. Continued at slow speed with no prob.<br />Now, I noticed the Pee hole not emiting like is should be. Could it be over heating due to pump prob.??? Purchased a Clymer B721 Man. and am troble shooting. You guys are the best, so that's why I'm here. Any suggestions...Thanx tons. Dmz
 
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Walter

Senior Chief Petty Officer
Joined
Jul 3, 2001
Messages
787
Re: Today's puzzler....? 40hp Merc.

Most respectable wrenches in here suggest replacing the water pump impeller every three to four years...more often if you're proned to running your lower unit through mud &/or sand. If you are not certain when your Merc's impeller was changed last, then you'd be wise to do so even if that doesn't resolve your current performance problem. What you describe could be caused by any number of things... You may be losing spark to one cylinder periodically, or perhaps it's something so simple as restricted fuel flow. Start with the easiest to troubleshoot and eliminate the most obvious things first. However, I'd certainly make sure that your cooling system is working properly so that you don't cause yourself any further grief in the event it's not.<br /><br />Good luck...<br /><br />Walt
 
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Dmzhmdepo

Seaman Apprentice
Joined
Jan 3, 2002
Messages
42
Re: Today's puzzler....? 40hp Merc.

Thanx Walt. Appreciate any info....I have found this site to be an amazing place for information on motors, and everyone is so willing to help.!!!! Thanx.
 
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Gold Bear

Petty Officer 1st Class
Joined
Sep 26, 2001
Messages
224
Re: Today's puzzler....? 40hp Merc.

I had a Merc engine that acted in a similar manner. Speeding up and down (without change in throttle control position).<br /><br />I found out that the fuel pump diaphram was stretched. After changing the diaphram it ran great.<br /><br />Just something to consider.<br /><br />Good luck!! Gold Bear ;)
 
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