1977 mercury 1500 inline 6 cylinder

ghigh1617

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Jul 25, 2011
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Hello Folks, I am new to the forum, but not to boating. I have a 1977 mercury 1500 inline 6 cylinder that I am having trouble with at the lake. When the muffs are on the boat sitting in the yard it starts good and runs good, when I get it to the lake and under a load it will not go, it boggs down and sometimes goes dead. I have rebuilt and cleaned the carbs and changed the spark plugs. I was at the lake the other day and it came up and ran pretty good, run out around 42 mph normally tops around 50 mph, when I went back to the lake a couple of days later it would not hardly run I managed to get it on palne one time and it ran o.k. but no speed then I set it back down to idle and it would not come back up. It started bogging down again, loaded it up brought it home and here I am any help would be greatly appreciated.

thanks ghigh1617
 

Bt Doctur

Supreme Mariner
Joined
Aug 29, 2004
Messages
19,092
Re: 1977 mercury 1500 inline 6 cylinder

guessing its an outboard ,so check the timing advance arm to make sure its not sticking
 

Chris1956

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Mar 25, 2004
Messages
27,033
Re: 1977 mercury 1500 inline 6 cylinder

A 1977 1500 will have a distributor. The timing cannot not-advance. I would recommend a compression check, and then crank her up and observe and listen to the spark plug cables to see if they arc to ground. if not, check the timing. You should see 4-6* BTDC when the carbs are just about to open, and 21*BTDC at max timing advance.

if those are good, the carbs may be set too lean to accelerate. Richen them a bit and retest.
 

CharlieB

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Apr 10, 2007
Messages
5,617
Re: 1977 mercury 1500 inline 6 cylinder

two stroke carbs do not have an acceleraqtor pump to provide additonal fuel for acceleration. They rely on an overly rich idle mixture. Idle mix must be set 'in-the-water' to best idle while IN Forward gear, PLUS almost another 1/8 turn richer for crisp acceleration.
 

ghigh1617

Recruit
Joined
Jul 25, 2011
Messages
2
Re: 1977 mercury 1500 inline 6 cylinder

two stroke carbs do not have an acceleraqtor pump to provide additonal fuel for acceleration. They rely on an overly rich idle mixture. Idle mix must be set 'in-the-water' to best idle while IN Forward gear, PLUS almost another 1/8 turn richer for crisp acceleration.
Thanks for your help. Should all three carbs be set the same way?
 

Chris1956

Supreme Mariner
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Mar 25, 2004
Messages
27,033
Re: 1977 mercury 1500 inline 6 cylinder

Each carb will need to be set independently. However, experience shows that the top carb runs a bit leaner than the mid carb, which runs a bit leaner than the lower carb. So the top mixture adjustment may be a bit more open than the mid carb, and the mid carb mixture ajustment may be a bit more open than the bottom carb.
 
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