Motor-tone changes at wot

[Big Jay]

Re: Motor-tone changes at wot

Hi nwcove ...

I'd say I'm about 80% sure... But I can't rule anything out at this point, very interesting.

Have you seen a carb make noise like this before? What would cause that?

 

[nwcove]

Re: Motor-tone changes at wot

not sure how dramatic the tone change is on your motor, but just for an example, i took my 7.5 out for its maiden voyage late last summer ( all new ignition and timing set with a fixture from F_R.....no carb kit as the motor ran wonderfully in the test tank). ran it up to 2/3 throttle and all was well.....any more and it went from sounding great to ...BLAHHHH, no drop in rpms or speed, just a noticable change in tone. opened the hs jet till the knob hit the cowl with no change in tone or rpms. reset the hs knob so i could get another half turn , and wow.....the motor went from what i thought was full power, to a bit to much for the little ten foot fg boat it was on, and the sound was day and night. this may not be your problem ( if you even have one!), but it sounds a bit like it?
also have a look at your mag plate when the motor is running.....does it wobble? if so, that can change the timing through the rpm range which will cause odd things to happen, easy fix tho. jmo

 

[aerobat]

Re: Motor-tone changes at wot

seriously - i guess you have somekind of vibration noise on the engine/boat wich sounds differently at various speeds and loads. i guess its harmless.

 

[kfa4303]

Re: Motor-tone changes at wot

+1. The motor looks to mounted at a reasonable height. If anything, you could raise it a bit until the anti-vent plate is level, or slightly higher than the keel. I actually built a small transom riser to lift my motor a bit. I suspect the change is sound may also be due to size and shape of the wake at various speeds, which in turn influences the sound. As long as the motor is pumping water, you'll be fine.