Mercruiser bogs and misses at high RPM

[mlegrand]

1988 Sea Ray with 260 hp Mercruiser 350 GM 5.7L eng. Thunderbolt IV Ignition. Was skiing today and it comes out of the hole just fine for about 3-4 seconds and when it gets above 3500 RPM's it starts bogging down. If you keep it at full throttle, it will run up to 4000 rpm or above and then bog down to 2500 rpm then run right back up to over 4000 rpm and back down like a seesaw. It will continue to do that. If you keep it at 3500 rpm or below, it will run fine. I have been sick so this is the first time the boat has been out this summer since being winterized last Sept. with Stabil in the gas. Have not run out that tank of gas yet. Have not changed the fuel filter for over a year since it was run very little last year. It was running fine when I put it away just before winterization. Has a cover on it but sits outside the house on trailer all winter and summer. Any suggestions where to look first would be appreciated.

 

[Wellcraft 89]

Re: Mercruiser bogs and misses at high RPM

Sounds like a fuel delivery problem.<br />Change the filter/also the one at the carb!<br />You could have a clog vent also.little critters like to build nest in openings.<br />The needle and seat on the inlet side attached to the float could be gummed up,not alowing full flow of fuel in the float bowls at max rpms.<br />Just some thoughts<br />Rich

 

[mlegrand]

Re: Mercruiser bogs and misses at high RPM

Thanks, Rich. I appreciate you taking the time to reply and I'm going to replace them.

 

[mlegrand]

Re: Mercruiser bogs and misses at high RPM

Resolution: Water separating filter was clean and no water in the filter. Removed the carburator filter and found it to be so clogged that only a few holes were left open in the filter screening. Replaced the carb filter with a new one and took it out today to run again with no other changes. Ran right up to 4500 rpms and was rock solid. Feels good, $1.88 filter fixed the problem. Filter probably had not been replaced since the boat was new. Paint was still on the nut that held filter in.