old mercy won't run in drive

j_kruggel

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Joined
May 25, 2015
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5
I have a 62 9.8 Mercury motor that starts and idles in neutral but a few seconds after I put it in forward or reverse it dies. The funny part is if I full throttle after its in gear it will run fine until I throttle back down and it dies. What could be causing this?

Thank you
 

tjdmercury

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May 21, 2015
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Carbs are dirty, after you put a load on the engine, the idle port arnt moving enough fuel.
 

j_kruggel

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May 25, 2015
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5
I have completely went through the carb and cleaned it, also put new gaskets on it.
 

j_kruggel

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May 25, 2015
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Could it be the idle adjustment? I have mo idea if I set it correctly when I put the carb back together
 

emckelvy

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Jan 16, 2004
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2,506
Could it be the idle adjustment? I have mo idea if I set it correctly when I put the carb back together

Most definitely! Screw the idle mixture needle all the way in (clockwise) and lightly seat it. Then turn it out (ccw) about 2 turns and see what happens.

That setting might be a bit on the rich side, but if you see a difference in the way it responds, you'll know that the idle circuit is pulling fuel. If that's the case, adjust the idle mixture screw for best idle with the motor in gear, in the water. Set the mixture on the rich end of the adjustment. Some of the old ones are really touchy about the adjustment, and it doesn't take much movement if the needle one way or the other to make it act up.

If the idle mix screw makes no difference, try adjusting it in a lot then back out a bunch. If no change in the way the motor runs, you're not pulling fuel up to the idle circuit and one of the small passages in the carb is still plugged.

Sometimes pulling the mixture needle and giving a blast of air/carb cleaner into the needle hole is enough to clear debris from the fuel passage. Worth a try, anyway.

One other thing I've seen happen on these old ones, the fuel pump design tends to get a check valve or 2 stuck open or leaking slightly from "trash" in the fuel. If that happens, it won't pump enough fuel at idle, even though above idle it'll do OK. Take the pump apart, inspect the (2) check valves and clean as necessary. A low-restriction fuel filter in the line before the pump will keep this problem from recurring.

But I'd look at the carb first; an easy way to diagnose a weak fuel pump is to pump the primer bulb and see if the motor runs better.

HTH & let us know what happens............ed
 

j_kruggel

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May 25, 2015
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5
So I adjusted the idle mixture and it seems to be idling now but when I throttle it dies
 
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