Sometimes when I start my motor/motors they sound and do this. What is happening here, They run fine but why?? Fuel Flow?? I have seen it on all 3 of mine motors before. Check the rpm gauge the audio might be a little had to hear and you can see the blower pulley react. Doesn't happen all the time, And these are SC800 572's.
Sorry, the raw video looked great but to big to load on OSO forum had to size it this one back without losing length.

IAC could be dirty Is it only one engine? Blower motors will Do this depending on air density / temp

Sounds like Blower surge to me. Mine would do it sometimes as well.

I think it sounds great!!!!!

Blower motor surge. Normal.

mine will do this if the throttle is advanced ever so slightly in the neutral postion. I to noticed this one time and slightly panicked because my boat doesn't have an aftermarket blower or procharger. It is straight stock.

What had happened is while taking off my boat cover I slightly advanced the throttle without knowing. To my relief I pulled the throttle back and it went back to normal.

Just my .02. I AM NOT a mechanic by any means and unfortunantly know very little about motors but it could be your idle is advanced too much if your throttle arm has not been bumped up????? Just a thought.

Thanks everyone

Slightly lean a/f at idle will make them surge like that. If you get them a little too rich, they tend to load up and/or stall, especially during docking when you are putting them into/out of gear alot. Could be just due to ambient temperature, specific fuel (quality/octane, etc). When my friends boat with a 250 B&M on it would surge at idle more than he would want to tolerate, he would usually richen it by 1/8 - 1/4 on the mix screws, but after that, then other days, it would act too rich and try to die. Was a fine line balancing act.

Good call I was stalling pulling up to the docks the other day. Thats always fun to have one or more motors stall when trying to pull into a dock.