Mercury Thundercraft sport-jet 90

[floyd36_]

Hi i have a mercury thundercraft sport-jet 90, 1994, and they start very great engine run great but i dont have power all cylinder pressure are 125psi, carb. clean, new plug, now i dont know were to look i no it seem like e need afjustement but were to look and what trouble shooting i have to do??<br />Thanks for your help!

 

[funpilot]

Re: Mercury Thundercraft sport-jet 90

Check your timing, a manual would help,<br /><br />and then the wear between the impeller and the wear ring. Sometimes that can make a big difference.<br /><br />Do you have a tachometer? What RPM does it run WOT? What speed are you seeing on your boat?<br /><br />Good luck,<br />fp

 

[floyd36_]

Re: Mercury Thundercraft sport-jet 90

i know i order manuel i will receive next week but anny help from you will apreciate and the timming does i have to remove the crank and how to check the timming??<br /><br />Thanks

 

[funpilot]

Re: Mercury Thundercraft sport-jet 90

Timing check, Wide Open Throttle:<br /><br />Remove spark plugs and ground the spark plug wires or install a spark tester.<br /><br />Remove the throttle cable so the tower shaft and throttles can move freely.<br /><br />Adjust all three carbs so the throttle plates are open together, and are completely horizontal plus or minus five degrees at WOT.<br /><br />Put a timing light on the top spark plug wire (#1) and crank the engine while manually holding the throttle plates and tower shaft open.<br /><br />Timing marks are at the front of the flywheel shroud, on the flywheel and shroud.<br /><br />Adjust tower shaft nut and linkage just below flywheel to 32 degrees before top dead center if needed. This is the cranking speed check. Normal setting for the boat is 30 degrees at wide open throttle but with the engine running, it is a difficult test to make.<br /><br />good luck,<br />fp

 

[Capt Ken]

Re: Mercury Thundercraft sport-jet 90

If I understand the broken english correctly, then he has a bad wear ring and impeller.