Outboard bogs under heavy load

[woodjm]

1996 Yamaha 75HP. Outboard will bog under heavy load. If there's just a couple of people in the boat, it acts fine. But it there are more people or I am pulling a wakeboarder, sometimes it will bog down and just give up almost. However, it never cuts off. What could this be?

 

[Triton II]

Re: Outboard bogs under heavy load

Hi Woodjm. Sounds like you are overpropped. Please give us a few more details - boat type, weight and prop type and pitch. Have you tried a smaller pitch prop - I had a F60 fourstroke a few years ago that cruised well with a 13.75 x 15", but bogged down and would run above 3500rpm with the same prop when pulling tubes and skiers. Changed to a 13.75 x 13" for the water toys and she was fine.

TII

 

[woodjm]

Re: Outboard bogs under heavy load

Thanks for your reply! The boat is a 1996 Key West 1720. Its weight is about 1150lbs. Engine weight is about 260lbs. So if i have 4 people in the boat total weight would be roughly 2100lbs. The prop is an aluminum 13x19. It didn't seem like I used to have this problem. I did switch to using one of those oil-gas mixture measuring bottles. I suppose it's possible the measurement marks are not accurate. Could too much oil in the gas cause this?

 

[99yam40]

Re: Outboard bogs under heavy load

If your rig has run better in the past the you need to be checking your motor out for problems,
Compression , spark on all cylinders, timing, and at the problem RPM not just idle.
Sounds like you may be loosing a cylinder. Maybe spark, fuel, etc.

 

[woodjm]

Re: Outboard bogs under heavy load

Yes I have read a little about losing a cylinder and it sounds like that could be the problem. When the problem occurs, I put it in neutral and rev it up a little bit, then put it in gear and usually it will get up and go again. Initially I thought the plugs were fouling up maybe due to too much oil, but i'm worried it might be more serious. I use 93 octane without ethanol and with yamalube oil. What are the reasons for losing a cylinder? Does this indicate a serious problem with the engine? Really just wanting to know if I need to take it to a mechanic to diagnose and fix the probelm or if it is something simple that I could do. When I noticed the probelm, I changed the plugs which didn't do anything. I also switched to using 93 octane instead of 89, which seemed to help because it happens less frequently, but it did not resolve the problem.

 

[99yam40]

Re: Outboard bogs under heavy load

water/trash in the fuel/ carb,
electrical problems(spark related)

I would have it checked out, you do not want to hurt a piston if it is running lean