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Charles, Marine Mechanic
Category: Boat
Satisfied Customers: 3869
Experience:  US Navy (Ret) Certified Mercury Marine Tech with over a decade of repair experience.
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Re: Can anyone tell what this rattling noise on my 120 Force

Customer Question

Re: Can anyone tell what this rattling noise on my 120 Force at high RPM is ? See V
I have an 97 120, just got a used boat with the Force on it. i rebuilt this engine with brand new everything reguarding the guts of it all except the reeds and the crank itself and the rods everything else has been replaced.. i have put atleast 55 hours on it with a good clean running engine little trouble starting it on a cool morning but would crank and stay running afterwords. . so!we Went to the lake for the 4th and and experienced the exact same noise between when running. it just sort of happened i was WOT and when iwas thrrottling down a slight clicking noise came about. When I first heard it, I pulled the throttle back thinking I blew something up. I kept running it for a while and also experienced a a WOT issue where it would run (what seems fine) for a few minutes and then start to have big RPM dips and act as if it was about to sputter out. I took the cowl off, looked for anything loose but could not find anything. The noise sounds really bad to me and has me worried as well. But another issue that bugs me, is after running for a bit... it will only hold an idle in either gear or neutral for 30 seconds or so. I had to re-start many times while moving in a no wake zone getting back to my trailer
the link below is my exact engine with the same sound like a clincking rattling noise. andi have lost power i am only able to go 35mph when before i was pushing 55 60
Submitted: 1 year ago.
Category: Boat
Customer: replied 1 year ago.
Expert:  Charles replied 1 year ago.

Hello, my name is***** will assist you.

You may have several different items going on. When slowing down, if you did so quickly, you could have been hearing the clutch slip inside the gear housing. This would be normal on a rapid slow down. The sound in the vid, actually sounds like reed slap from an over speeded engine. There may be one or more bro***** *****s inside the intake. That would also count for the power loss. Remove the carbs and get a good look at the reeds, make sure that they are still there and intact.

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