1977 Mercury 75 starts, then stalls

lumpy_63

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Joined
Aug 30, 2006
Messages
23
Out on Scofield reservoir in Utah, tried to start Mercury 75 (7.5 hp) trolling motor (choke on); motor starts, then stalls. Could only keep it running by applying about 1/2 - 2/3 choke; even then it didn't want to idle. Started up the main motor (Suzuki DT65 65 Hp) and went back to the dock. At the dock, both motors do the same thing (want part choke to keep running, and neither wanted to idle). Degenerated to the point where neither motor would stay running at all; when I started either one and applied throttle it sounded like they were choking and stalled. Got the boat home and checked fuel level in tank (3/4 full). Checked fuel filter screen in Suzuki (clean as a whistle). Any advice on what else to check? Thanks.
 

lumpy_63

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Joined
Aug 30, 2006
Messages
23
Re: 1977 Mercury 75 starts, then stalls

The vents are open (both motors share a common tank). I checked to see if there was an obstruction in the fuel line by removing the fuel line after the bulb, then pumping the bulb - I got plenty of fuel. I checked the filter screen on the Mercury; there was a little debris, which I removed, but it still had the same symptoms. Now I am wondering if it was coincidence; maybe the fuel pump died on the Mercury (the pump is in the carb), and the Suzuki has another problem... Just not sure yet. Thanks for the reply!
 

emckelvy

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Joined
Jan 16, 2004
Messages
2,506
Re: 1977 Mercury 75 starts, then stalls

Wonder if you got some bad gas; perhaps the carbs on both motors got a load of water.

Sounds like the carbs need to come off; float bowls removed; everything (including idle jet passages) blown out with carb cleaner then compressed air; any faulty parts replaced; then reassembled with "carb packing" kits.

The kits should be readily available and are relatively inexpensive compared to the factory's "rebuild" kit.

You likely won't need a rebuild kit anyway to service these carbs; the packing kits will have the "consumables" you'll want to replace (gaskets, fiber sealing washers, etc) when you reassemble. If you find a defective float or needle/seat, these parts are available separately.

HTH & let us know what you find..........ed
 

lumpy_63

Cadet
Joined
Aug 30, 2006
Messages
23
Re: 1977 Mercury 75 starts, then stalls

Thanks for the suggestions. I will go through the carburetors.
 
Joined
Jun 1, 2010
Messages
18
Re: 1977 Mercury 75 starts, then stalls

I really hate when people dont come back to let other people know how it turned out. I had a simular problem with a mercury 85! It turned out to be that the hose in the fuel tank was SUPER loose at the top connection. It was pumping more air into my carbs then gas. Anyone who has pulled theirs off know that it is next to immposible to put a clamp on it. The only way to fix this is to cut an inch or so off the end and reattach or just replace the line. Gasoline will begin to eat anything that has sat in gas over a long period of time. After I fixed this, it went from running at 60% to 110%. A lot of people will overlook the gas tank for problems. If your engine runs great with a full tank and not so good with a low tank, check your tank hose!
 
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