yamaha f40 bhwt problems

[morriman]

Hi, as this is my first post i will do my best in explaining my problem with my 40hp 4 stroke 2002 motor complete with tiller and hydraulics fitted to a 4.35meter aluminium boat.
When i start the motor and motor at 0 to 10 km no problem but between 10 and 15 km the motor shakes causing an amount of vibrations through the boat , after 15km and above no problem no shakes etc .The motor never had this problem, serviced the motor twice since the vibration started and still cannot solve the problem .,it makes it a bit uncomfortable when motoring at the 10km to 15km .Do you think i should worry about the vibration or does anyone have the same problem .Recently i have had the drive shaft bearings replaced and fitted a new timing belt along with waterpump and extras but it has made no difference to the vibration .can it be the propeller or does the motor have some sort of balance mechanism .
any help would be appreciated
cheers From Australia
Morriman

[boscoe99]

Other than being balanced during manufacture there are no additional balance mechanisms on the F40B model.

If the propeller shaft were to be bent I would suspect that vibration would be greater as the RPM increases and not decrease with the boat speed is above 15 km. Have you inspected the propeller shaft?

The F40B model, here in the USA anyway, has the worst reputation for carburetor problems than any other Yamaha model. If there is no damage to the propeller, if there is no damage to the propeller shaft, if the motor is securely attached to the boat and the motor mount bushings seem to be in good shape, then my initial guess would be that the carburetors are in need of cleaning and a sync and link procedure. There are idle circuits within the carburetors, mid-range circuits within the carburetor and then high speed circuits within the carburetor. Those circuits use incredibly small passageways. Just a bit of debris within the carburetor can cause havoc at different engine RPMs.

Just a wild eyed guess from thousands of miles away.

[morriman]

Thank you for your reply,i really appreciate your info and will go and talk it over with the outboard mechanic pretty sure he said he has cleaned out the carbys . once again thanks

[panasonic]

Thank you for your reply,i really appreciate your info and will go and talk it over with the outboard mechanic pretty sure he said he has cleaned out the carbys . once again thanks

Take a video if possible so we can see how bad the shake is.