Originally Posted by bdbwtie

I have a mercruiser 502 serial im guessing is OK173702. It is in a 98 powerquest. Cold it runs like a champ, good oil pressure, no surging. After the engine is up to operating temp, guage shows 160 and I come into a no wake zone the engine will hunt. I usually try to pump it slightly off throttle just for sake of thinking its gonna stall. It isnt enough to make the tach fluctuate, but you can definelty hear the engine varying in rpm. If the no wake zone takes awhile to get through the engine almost seems loaded up, trying to take off it feels flooded, can tell its not responsive and sounds loaded. Usually giving it more throttle or coming off the throttle and then back on will clear it up within 5-10 seconds but doesnt seem right. I have noticed alot of black on the transom and under swim platform after every use. Any ideas what to look at, or being fuel injected am i stuck to having it scanned?

Originally Posted by F-2 Speedy

you need a scanner to check the timing, timing must be set in base mode

EDIT, Ive had a few 502 mag mpi like yours and the water flow was always very equal out of both pipes

Originally Posted by bdbwtie

I was told you could put it in base mode with a paper clip and check it, this not true? I did talk to a marine shop who thinks its due to the fuel system having paint on the inside and clogging injectors. Which may be true, but most everything ive experienced with clogged injectors ran like crap all the time, not just warm and at idle. Of course they cant get it in until after the fourth. As far as the water I understand the path of least resistance, put I never seen a through hull not spraying. Repair shop wondered about silent choice baffles being hung up so I will look into that as well.