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1989 Mercruiser 5.7l Randomly slowing down/dragging?

Chadbud

Member
Hey guys! I hope you all are doing well. I got an issue that’s confusing my inexperienced butt off!


I bought a 1989 Celebrity 208 SE 21’ this year in April from a local marina. The boat is in magnificent condition. It was owned by a marina mechanic who bought it new back in its year. He kept it indoors in the off season and has all maintenance/work order documentation.


The boat had been running great. The only work the marina did on it prior to me purchasing was replacing liquids, all filters, bellows, anodes, and shift cable.


During a few trips to the Allegheny River (I’m from Pittsburgh) I noticed that around half or 2/3 throttle, whether I’m towing a tube or skier, the boat would lose power. It almost felt like I ran over a big patch of seaweed and I was dragging something all of a sudden. It’s the same feeling a passenger gets in a car when they slow down quickly.


As far as my memory serves.. RPMs did not change. I could give it more gas and it would try to pick up but then slow down again. That’s when I would decide to bring it back to idle for a little before putting her back on plane. She would do great for a while and then the same thing would happen. Engine turns over and starts perfectly. No other issues were present.


After some research I figured it could be a spun prop hub or engine coupler (god I hope not!). I brought it to my mechanic who’s been in the field for 30 years and he said the shift cable (if memory serves me correctly) was not adjusted properly. He made sure to express that if that cable is not adjusted properly on this engine with a SS prop then it can cause my issue. Fuel filters are brand new from marina I purchased it from.


I was so relieved and took the boat back out to hopefully enjoy the rest of the summer taking the family boating. After two days of boating the engine was running FANTASTIC. Felt like I had more out of the hole power and I was satisfied.


However, last weekend I was pulling a skier (my dad!) behind the boat on my way back to the launch to finish the day and I felt that dreaded drag again. As soon as it happened I dropped the RPMs to cruising and things seemed fine and then it happened again so I cut the engine and pulled my father in. I brought her up on plane once more before getting to the launch ramp with no issue.




Thats where I’m at! I’m probably going to bring her back to my mechanic but I’m just really frustrated. I haven’t taken my family boating in YEARS. I just really want everyone to be happy. I’m hoping I can get some insight from this amazing community.


Thanks again! I’ll answer any questions as soon as I get them!
 
Sounds like fuel starvation. Have your mechanic put a fuel pressure gage on the motor and see what happens.

Jeff
 
Ayuh,..... Does the motor rev up wildly when you feel the drag,..??..??

If not,.... I agree with Jeff,....


the RPMs stay almost exactly the same when I feel the drag and decrease in speed. The RPMs may even drop slightly.

My plan is to take it back to my mechanic and have him assess fuel lines. HOWEVER, I can’t do that until after 4th of July. Family is expecting to go out for the holiday on the boat so If I can’t figure this out on my own then I have to wait until after the 4th to drop it off at mechanic since he reports being 2 weeks backed up for work.
 
Bump.

Fuel filters are all clean and like new. I pulled gas cap half way out to see if it was the fuel tank not being able to vent to equalize air pressure. Boat has had about 60-70 gallons of 90 octane fuel ran through it since I bought it and problem began. I’m at a loss. Maybe a carb rebuild? But that will cost me 300 bucks. Hopefully it’s something else.
 
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