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BradY_83

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Posts: 13
Reply with quote  #1 
Is anyone able to tell me if the butterflies on a 90 etec should be 100 percent open or not quite when at WOT.

Also is the fuel filter under the cowling a disposable item or do you take it off to back flush or clean and re install it?

Having a go at doing as much service and maintenance work as possible and keen to learn as much as I can.
rickmcd53

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Posts: 1,186
Reply with quote  #2 
The fuel filter is disposable, if you have an on board filter you may never need to change the one on the engine. On my first 75hp, I ran 1500 hours in 4 years, changed the onboard filter once a year, never changed the engine filter.
The throttle plates on the I-3 engines do not open but about 85% from the factory. The throttle rod can be lengthened some by unscrewing the end that snaps on the ball.. Some owners have reported up to 200 rpm gain at wide open throttle while others have reported no performance gains. As long as you are turning 5200-5300rpm you should be good.
BradY_83

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Posts: 13
Reply with quote  #3 
Thanks mate. I will see how it goes tomorrow when it gets on the water. If it seems to help I might go there but I’m searching for lost revs and im hoping carbon clean/injector clean will help, as well as calibrating the TPS.
BradY_83

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Posts: 13
Reply with quote  #4 
Happy to report the engine tuner and a dose of the fuel treatment has got me back to 5200rpm and its running smooth as butter. I still think a prop change is in order as I didn’t have the usual loading in the boat today. Gave it a real good burn at WOT. Just the sender to fix now and I’m happy.
rickmcd53

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Posts: 1,186
Reply with quote  #5 
Brad, dropping 2" in pitch would help and your max rpm should be about 5200 with your average load. If you run it lite, there isn't much speed gain above 5200 since that is where peak hours is but the mechanical parts of the engine can handle 5600 rpm.
My 90 is underproped a bit, turns 5600 with my normal load but drops to 5200 with 4 extra people on the boat. I like the low end power and if lightly loaded just back off the throttle a little. For my use I don't mind giving up one or two mph on the top end to gain the convince of not having to switch props when loaded. Another hint, carry your current prop as a spare and remember to get an extra nut, washer, and cotter pin.
BradY_83

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Posts: 13
Reply with quote  #6 
Thanks mate. Yes I was thinking of dropping back to a 13” 4 blade or a different shape 15”. From what I understand the viper isn’t really a good prop for carrying bigger heavier loads and the hull isn’t a speed hull, just a fairly plain v hull design.
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