Mercury 4 stroke 25 efi 2010

by Jim
(Denton, NC)

wide open rpm drops as engine warms up. Example early in the morning 5300 rpm, no problem. Run 10 minutes down the lake and rpm drops to 5200. Stop and fish a while and when restart it is down to 4800 max. Boat loaded with 2 people, lucky to get 4400 rpm. Have changed plugs, check both low pressure fuel filters (tank and in line) all ok. Checked compression (cold) and had 150 on top two, but #3 showed 90 psi. Not sure if it was a good check since it is hard to get to. But has not dropped since previous check a year ago. Talked to local Merc mechanic and he said he had no idea what could cause this. What about timing issues? Any thoughts would be appreciated. Thanks.

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