200hp Yamaha loses power @ 2500RPM

1998 200 V6 Yamaha has been running fine. Starts up, Idles ok, no overheat, Oil full. When applying throttle, gets up to 2500RPM then sputs RPM down to about 1200 or so and back up, up and back down again. Throttled back to idle, idles OK, returned to dock. Replaced dirty water/fuel separator filter, still same problem.<br />I know its repair should be simple as motor has been running great. This is an all-of-a-sudden event. <br />Any Ideas?. Where should I look next?

Re: 200hp Yamaha loses power @ 2500RPM

Sounds like one of the two fuel pumps have gone bad. Usually one will only feed enough fuel to carry the engine up to the 2000 mark and it takes the second to get it further. Common problem. You can be sure by having someone squeese the primer bulb when this happens. If the engine picks up and runs, then its the fuel pump. If not, then its something else.

Re: 200hp Yamaha loses power @ 2500RPM

Thanks Capt Ken, Would your suggestion about the fuel pump be under or not under load? Because with I rev'd it up, it went to over 4000prm with no problem? But under load, it did as I said earlier.<br />Thx<br />Bill

Re: 200hp Yamaha loses power @ 2500RPM

In a no load case, the engine will rev up because it don't take the same volume of fuel to rev in neutral. Plus the carbs are full from idling and you wouldn't have the courage to hold the throttle open long enough for them to run dry.

Re: 200hp Yamaha loses power @ 2500RPM

Capt Ken, Thanks and your analysis sounds very logical. Like I said, I know its gotta be something fairly simple. I'm more familar with older auto engines and I've replaced or rebuilt fuel pumps over the years many times but boat engines have kinda stumped me. The redundancy of two fuel pumps is an example but I understand why the redundancy. From your experience, should I replace both pumps? I'm not sure how to isolate the faulty one or should I just replace the diaphram(s)? <br />The part,6E5244710000 Yamaha Fuel Pump Diaphragm, was found in iboats. though it does not state whether its for a 1999 200hp or not. Are they generic for all yamaha's?<br />thx<br />bill

Re: 200hp Yamaha loses power @ 2500RPM

Capt Ken, No need to respond to last correspondence. You were right! Fuel pump or pumps was/were the culprit(s) and easy to replace. I decided to replace both of them for less than a $100. Felt that what the heck, if it wasn't corrected, at least I knew the pumps weren't the fault, and wouldn't be for awhile. I replaced BOTH of them, took about an hour, took it out for a test and, Done Deal! For now, I'm one happy guy. Ran like a charm. Thanks very much for pointing me in the right direction. <br />Very Best regards and,<br />Good Fishing,<br />Bill Darnell<br />Jacksonville

Re: 200hp Yamaha loses power @ 2500RPM

oops, spoke too early. Yamaha ran good first out like problem was solved by replacing fuel pumps. but next day, loaded fishing rods and took off. almost identical problem. Unless I applied throttle slowly. Once past the 3000 rpm mark, could gradually get up to, without balking, 4200rpm when applying power slowly. When throttle applied quickly, couldn't get past 2000rpm? Any more analysis?