1975 mercury 85hp not starting

riverrat4life

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May 6, 2012
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So i turn my motor over and it fires once and then dies right away. Its getting good spark just replaced the plugs and tested them and also is getting gas the carbs have been cleaned up and rebuilt. Im thinking it could be the switchbox or the trigger how would these to see if thats the problem? Whats throwing me off is that it turns over untill it fires once and then quits turning over? what would cause it to do that?
 

riverrat4life

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Re: 1975 mercury 85hp not starting

I have also noticed that as soon as it fires and dies the piece that engages the flywheel from the starter comes back down but still spins with the key turned.. and that the yellow wire coming from the throttle assembly to the starter solenoid loses power as soon as the engine fires once? could this be related to the problem of it dieing after firing once or is this how its suppose to operate as soon as the motor fires?
 

Chris1956

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Mar 25, 2004
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27,036
Re: 1975 mercury 85hp not starting

When the motor fires, the starter gear is supposed to disengage. What you are seeing is normal. If you have good spark the ign system including the trigger and switchbox is fine.

Are you choking the daylights out of it? Pump the primer bulb hard, cold start lever all the way up, hold choke button and crank her until she starts and runs. When she begins to die, let up on the choke.
 

riverrat4life

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May 6, 2012
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Re: 1975 mercury 85hp not starting

When the motor fires, the starter gear is supposed to disengage. What you are seeing is normal. If you have good spark the ign system including the trigger and switchbox is fine.

Are you choking the daylights out of it? Pump the primer bulb hard, cold start lever all the way up, hold choke button and crank her until she starts and runs. When she begins to die, let up on the choke.

yea i have tried everything choking it hard and have the cold start lever all the way up and it keeps doing the same thing as soon as it fires once just dies on me.. is it possible that something in the switchbox is busted that when box reads that it fires once just cuts the ignition off instead of in a running mode
 

xanderman

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May 12, 2012
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7
Re: 1975 mercury 85hp not starting

yea i have tried everything choking it hard and have the cold start lever all the way up and it keeps doing the same thing as soon as it fires once just dies on me.. is it possible that something in the switchbox is busted that when box reads that it fires once just cuts the ignition off instead of in a running mode

The switch box does not switch modes from start to run, what is happening is that the engine fires and begins to rotate faster than the starter, disengaging the starter gear from the flywheel gear. the starter continues to turn as long as the key is held in the "start" position but is not engaged with the motor.

i suspect the engine is actually starving for fuel, while there is enough to initially fire once it is used up there is insufficient fuel to maintain it.

Check that the choke fully closes the butterfly valves/choke plate, the primer bulb is firm, fuel filters are clear, good fuel.

If the carbs are recently rebuilt have they been tuned, has it been run since the rebuild? The idle screws may have to be turned out a bit to make it a little richer?
 

aussieflash

Lieutenant Junior Grade
Joined
Feb 5, 2011
Messages
1,004
Re: 1975 mercury 85hp not starting

Starting puts a huge load on battery.Maybe battery is at fault (bad cell) and is not recovering after numerous attempts at starting.Should give batt and starter a breather in between sessions.If battery tests ok,id be looking at choke.
 
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