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150hp merc black max outboard

gbfd10

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"<font color=""ff0000"">i have

"<font color=""ff0000"">i have a 1989 merc 150 hp black max and my lower unit went out a friend of mine had a 1981 200hp merc we swapped them and took it out and the boat wouldnt move my question does the 200hp have a different gear ratio than the 150 and if so if i put a 18 pitch on it would it help ?</font>"
 
What do you mean by "would

What do you mean by "wouldn't move"? Wouldn't move at all? Or wouldn't move as fast?
 
"<font color=""ff0000"">there

"<font color=""ff0000"">there is a 21 on there now and it wouldnt go above 1500 rpm
</font>"
 
"Dan, if all else was "nor

"Dan, if all else was "normal" dropping to an 18 pitch from 21 would gain you about 600 rpms - still far short of the over 5400 you should be getting from that motor.

It sounds like your problems extend beyond the prop. While the gear ratio's between the 150 and the 200 may have been different as well, it still wouldn't account (on it's own) for only turning 1500 rpms.

It's time to start troubleshooting with the basics - compression check, spark check, fuel system, ignition component checks...."
 
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