Mercury Bigfoot 60 throttle issue

[Glenn R Williams]

All: weird issue. I have a mercury Bigfoot 60, 2007 model. I bought the boat 2 weeks ago and put it in the water last weekend for the first time. The boat and engine sat up for approximately 2 years. After putting in, the engine initially would only turn up around 4000 RPM and run about 14 MPH. Since it was the first time out I thought this was normal until We took a break at a marina. After leaving the marina the engine suddenly gained about 1500 RPM. I thought it might have been Fuel since we purchased 11 gallons. The rest of the day the engine ran and went to wide open throttle with no issues.

I ran around 54 to 5500 hundred RPM and 18 Mph.

fast forward to today. Same issue. We ran to the end of the lake at 4000 rpm wide open throttle. Then after idling in a no wake zone for about 10 minutes, maybe longer, I saw the tach needle jump from idle to around 6 or 7000 rpm. (Just the needle, not the engine). After exiting the no wake zone the engine went to 5500 RPM, ran fine the rest of the day.

any clues? I read somewhere about "guardian" not sure what that is.

Here re is what I have done to the engine so far

pulled the plugs and no abnormal indication noted.
changed the water pump impeller
the original fuel injection fuel pump was locked up so changed that in the vapor recovery tank with new seal
changed the voltage rectifier (system was not charging)

could this be ECM related?

Help

thanks
Glenn

 

[Glenn R Williams]

Well after much head scratching and going through everything I could think of, I performed a compression check, all good. Pulled the mechanical fuel pump, all good. Pulled and replaced the primer bulb and new hoses, changed out both fuel filters. Then I pulled the spark plugs and found the #3 plug was wet and the porcelain was pure white. Had gas smell so no water. Went and bought a spark plug tester, checked and verified that the coil pack was dead. Bought a new one from West Marine here in Fort Worth and installed. Now hitting on all cylinders. I will say this, the engine ran glass smooth on 3 cyclinders and at full throttle you would have never guessed you were down a cylinder. No abnormal vibration at all.

well hope this helps someone.

Glenn