got a rpm range pattern HUMMING

[bob johnson]

if I back off just a little it goes away..... this is at 5000 rpms.......

any one have an idea whats causing this rugh .rugh .rugh. rugh.?

as a side not the motor does have a cough at low rpm.....1100 or so....under power


thanks....

View video

 

[jakedaawg]

Is it noticeable in the tach? Sounds to me like a manifestation of a fuel restriction or air restriction on one hand, or a changing load on the motor. Is the vessel porpoising at all?

 

[bob johnson]

it is unnoticable on the tach.... and the boat did not porpose...it was a smooth as can be.....just a sound...and if I slowed just a little...it went away....and became that constant hmmmmm.....that you love to hear.....