Need a Yamaha Mech to Reply Please!!!

Hello All, I'm new to this forum and I need some help. First "yes" I used the search function. <br />I have a 1987 90hp Yamaha, coming in the other day the motor started making a faint knocking / tapping sound that is consistant with the RPM. When I run it up above 4400rpm to WOT it surges like I'm closing the choke butterflies on and off. Any ideas what may be going on? I use ring free at every fill up so I don't think I have a carbon issue. Plugs are clean, linkages are okay.<br />Any and all help is appreciated, thanks in advance.<br /><br />JR

Re: Need a Yamaha Mech to Reply Please!!!

not sure? but it sounds like two different problems.<br />surging is usually caused by bad fuel pumps.<br />knocking could be warning sign of something about to let go? connecting rods? <br />agian, no expert on 90hp's but seeing as no-one else responded?<br />maybey describe the problem more specificly and others will jump in?<br />mike

Re: Need a Yamaha Mech to Reply Please!!!

Thanks for the response Mike.<br />The tapping or knocking sound and the engine surging all happened at the same time. I was just leaving the grounds on my way home and noticed the engine sounding different, I could hear the tap or knock. You don't hear it at idle and it goes away over 4200 rpm (which is what I cruise at) but then the motor surges dramatically like it's starved for fuel. Am I hearing a knock under load due to a lean mixture problem? Would it be present throughout such a large rpm range? I am at a loss here and really appreciate any info or feedback from some that may have experienced the same issues. Once again this is a 1987 90hp. I purchased last year, it has about 1500 hrs on it. I knew the owner, he was an elderly man who went for an hour ride on the weekends so it was never abused. <br /><br />Thanks,<br /><br />JR

Re: Need a Yamaha Mech to Reply Please!!!

Have you changes your fuel to a different octane?

Re: Need a Yamaha Mech to Reply Please!!!

test page

Re: Need a Yamaha Mech to Reply Please!!!

No, I've been running the same fuel from the same marina. I was probably 3 gallons into the last fillup when it started. The noise stays consistant with the rpm. Keep the replies coming!!<br /><br />Thanks

Re: Need a Yamaha Mech to Reply Please!!!

Took the air silencer off today and ran the boat out in the bay. There is no noticable spitting from the carbs, but i can here the tapping sound clearly. I wonder if it sucked a reed? Checked the fuel lines and filters, all clean. Still surging madly over 43 - 4400 rpm.