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Old 11-16-2014, 01:31 PM   #11
Lt. Commander
Join Date: Apr 2011
Posts: 109

Originally Posted by mmwjr View Post
There is a fuel filter in the carb when the gas line connects. Disconnect gas line then undo large nut to access filter.

If you stay below 3/4 throttle does the boat run fine all day? If yes then this should eleminate a clogged vent.

Not sure I understand how it would cause the issue but since tach is misbehaving remove the gray wire on the S terminal (wrap it in tape to ensure it does not short to anything) from it and see if the problem goes away.
That filter was changed when the carb was rebuilt.

I think it is just a bad tach gauge. I pulled the under side cover out and checked the connections, pulled and cleaned the wire connections, and replaced. Still doesn't work at all. I am going to have the timing checked and be sure the fuel pump has adequate pressure at the carb.
Is there any way the oil pressure switch is malfunctioning and causing the pump to shut down at higher rpms?? The gauge reads plenty of pressure but I have heard of those switches being bad. Although it seems they usually wont allow the boat to run at all.

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Old 11-16-2014, 03:07 PM   #12
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Join Date: Feb 2012
Location: Perry Hall, Maryland
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The oil pressure switch has two staes open or closed. Since the boat does not die and the fact that it would at lower rpms when the pressure is lower means the switch is not the issue.

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Old 11-19-2014, 07:13 AM   #13
Join Date: Nov 2014
Location: Perth Australia
Posts: 6

Not really familiar with Mercruiser motors but I have had the same thing happen on a motorbike
After many hours and plenty of $ I found that the carby float was a little too low causing it to starve at high rpm

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