650 65 hp 4cyl suddenly slower

[bucksaw]

My 650 65HP 4CYL is on a 16 foot fiberglass cutter. It has been doing 30 miles per hour all summer until today. It is docked all summer, and bottom has antifouling paint. Motor doesn't seem to rev any different just seems like i am draging the ancher and speed is only 19 mile per hour from 30. Could a slipping prop act like this without reving up, or could it maybe be water in the floor. I have had an automatic Bilge pump and has seemed to be working fine all the time. Any thoughts on this would sure be a great help. Thanks

 

[papasage]

Re: 650 65 hp 4cyl suddenly slower

could have lost a cylinder due to no gass or no fire or no compression check those 3. with a cylinder not firing it will idle good and rev out of gear . it just waon go in gear . you can ruin a cylinder running with no gass going to it.

 

[bucksaw]

Re: 650 65 hp 4cyl suddenly slower

It go's in gear and runs fine no miss or anything, I just don't have the speed i had. I don't have a tach, just gps tells me i have went from 30-19 miles per hour. And feels like it's pulling another boat, maybe I guess i might have water under my floor or something. I'll have to pull it out next week and start ripping the floor.

 

[papasage]

Re: 650 65 hp 4cyl suddenly slower

you can loose a cylinder and the onley way to tell is to pull 1 plug wire at a time and find the one that doesent make a change in the sound of the motor .i would srart with the one that is the the wetist plug .

 

[bucksaw]

Re: 650 65 hp 4cyl suddenly slower

Found out why i lost speed. I was told to use Synthetic blend oil, and i wouldn't have much smoke. Well didn't have any smoke, but went from 30 mile per hour to 19. Dumped that fuel in a can and went back to my old oil mix that is not synthetic,now back up to 30 again. My motor is a 1969 650 guess I made a big boo-boo trying to run synthetic oil in her.