898 mercruiser bogs - goes to 2200 rpm then immediately stays 1t 1700 rpm

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turner1l

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Jul 21, 2011
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1978 898 mercruiser idles and shifts but when we take off it will not go past 2200 rpm and then run a little rough then immediately drops down to 1500-1700rpm. We have a 4barrel rebuilt carb on it. Just emptied old fuel and put new spark plugs in it. Runs great in idle. We never have ran this boat in water, so unsure about prop. Running cool temp but when wot, rpm jumps up then back down. (We put new gas in older fuel filter, due to wrong fuel filter was given to us) Also removed check valve by gas tank; we will clean it and replace.
 
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turner1l

Cadet
Joined
Jul 21, 2011
Messages
9
Re: 898 mercruiser bogs - goes to 2200 rpm then immediately stays 1t 1700 rpm

Please help me on this problem. My engine does not stall when wot, it just will not go over 2200 rpms and then drops to 1500 rpms and continues to run. Is this the fuel filter? what else can cause it to lose power but continue to run at low rpms...
 
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turner1l

Cadet
Joined
Jul 21, 2011
Messages
9
Re: 898 mercruiser bogs - goes to 2200 rpm then immediately stays 1t 1700 rpm

We thought carb was ok... but noticed black residue on one port, completely clogged. Removed air intake? from top of carb, cleaned with brake cleaner and blew out all black residue from bad alternator belt and also recleaned carb and opened all ports so other 4cyl could kick in. Now it runs smoothly. We replaced alternator belt today and will check. ( we rebuilt 4bar carb and didn't suspect it was dirty, etc.) Do we have to have that syphon/check valve before in front of the gas tank? thanks
 
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