Motor slow acceleration then overheat

[Asmikle1]

A few weeks ago I ran my 88 mercury 175 black max and it ran okay but slow to WOT but got on plane and run full speed. Once I slowed down and tried to speed back up (wake zone) the temp horn sounded so I shutoff and trolled to dock. Why I got home I cleaned the carb (soaked in chem) and replaced gasket and needle. Also replaced fuel pump gasket, added fuel separator, spark plugs. Out of water with muffs it cranks and runs good idle for 30 minutes and revs up but today I took back to lake to run. It cranked but when I left to dock noticed it run like it was bogging down so I gave it full throttle it slowly accelerated and for few seconds them it went WOT on plane but the temp horn came on again. I returned to dock again. I check the compression and it is 108 to 110 all 6 cylinders. Any help would be great. I also changed the impeller and tested the thermostat

 

[Dukedog]

jus tha impeller?.. needs complete pump kit.. might consider a poppet kit also.. comp is a little low but that may easily be your gauge..

 

[Chris1956]

Check the torque on the cylinder head bolts. I have had those engines have them loosen up over time.

Are all cylinders firing? Are all spark plugs the same color?

 

[Asmikle1]

The impeller, housing , and gaskets were replaced (kit). I will check to see if all cylinders are firing and check torque on the bolts.

 

[Asmikle1]

Who has the best service manual for the Mercury Black Max V175 1988 (Serial# OB220902)

 

[Asmikle1]

I was able to test the spark on the motor. 2 4 6 has a spark but 1 3 5 (left side) no spark. Is it the switch box or possible stator?

 

[Chris1956]

Switchbox issue. Best to replace both of them.