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Old 26 May 2012, 15:30   #1
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HELP ASAP PLEASE... 2nd hand Yamaha 50hp wont rev over 1700 rpm, should I buy it?!...

Hi there,

I looked at a boat I won on ebay today which is meant to be in very good "as new" condition and the engine has only done 44 hours use according to seller/Yamaha tachometer/computer.

The 50hp engine is a 2003 I think, Its in very good condition, well looks wise, looks like new!!

but when we went our for a test drive in it, the boat got onto plane, but would not go faster than 1700rpm (the manual says it should rev to 5500rpm!) in forward gear. In neutral I revved it to 3000rpm but the ebay seller didnt want me to go more than that! The ebay seller is selling it on behalf of someone else, who used the zodiac as a diving boat, it comes with a brand new spare prop, I wonder if that was the original prop and the one fitted is of a different pitch to help pull the boat onto plane when fully loaded with people/diving equipment? But if it did have a lower pitch prop, would this really make the engine only rev to 1700rpm when in gear? like I said it reved to 3000rpm when in neutral.

Does this sound like a major problem? The engine honestly looks in FANTASTIC condition, especially under the hood, and it idles fine (at 400rpm which I thought was low, should be 700-800rpm!) but just didn't rev more than 1700rpm at full throttle!

I am hoping its simply a throttle arm that needs adjusting or something?!

Any help will be greatly appreciated at I am meant to be going back to see the boat tomorrow, and I have actually bought it on ebay, but was told it is "as new condition" so if we cannot work out why its only reving to 1700rpm then I will walk away and tell ebay item not as described if the seller kicks up a fuss!

Thanks for your help,

James.
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Old 26 May 2012, 15:50   #2
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Take another viewing and disconnect the throttle linkage from the engine and manually move the throttle on the engine. If its been home maintained or rigged it might be that it's been set up wrong. At least you can discount the engine being wrong of it works manually but not in remotes.
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Old 26 May 2012, 15:57   #3
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good idea thanks, don't suppose you have a picture showing what is what? as there a quite a few linkages and I wasn't sure which was which never mind the throttle! =(
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Old 26 May 2012, 16:03   #4
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Any chance the revometer is miss calibrated, especially as it seems I be idling at around the same ratio lower as the max rev would be?
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Old 26 May 2012, 16:09   #5
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Where are you/the boat based James?
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Old 26 May 2012, 16:33   #6
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Quote:
Originally Posted by elvis View Post
Any chance the revometer is miss calibrated, especially as it seems I be idling at around the same ratio lower as the max rev would be?
Not a chance (I did wonder this for a moment) because my 25hp Yamaha on my boat at WOT has a fair bit more poke than this 50hp Yamaha at 1700rpm. Also it was very obvious the 50hp engine was hardly trying hard at 1700rpm, and it was also very quiet! Not a chance in hell the tacho is out, as in the 1700rpm shown was really 5500rpm!

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Originally Posted by benc View Post
Where are you/the boat based James?
Essex (southend) why you ask?
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Old 26 May 2012, 17:21   #7
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I had an engine with the same symptoms, it was a knackered stator.
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Old 26 May 2012, 17:37   #8
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It's not the safety rev limit cutting in is it? Low oil or over temp.
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Old 26 May 2012, 17:46   #9
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Try putting the original prop on it and try that, if she still won't rev, then start to think about the throttle linkage!
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Old 26 May 2012, 18:01   #10
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Tell them you'll pay full whack if they fix it. Don't go striking deals-you don't know how much it'll cost to fix.
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