HELP ASAP PLEASE... 2nd hand Yamaha 50hp wont rev over 1700 rpm, should I buy it?!...

J@mes

Seaman Apprentice
Joined
Apr 11, 2012
Messages
49
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.
 

99yam40

Fleet Admiral
Joined
Sep 7, 2008
Messages
9,039
Re: HELP ASAP PLEASE... 2nd hand Yamaha 50hp wont rev over 1700 rpm, should I buy it?

never buy a broke motor, is my moto.
If he can get it serviced and running properly then have another look
 

multimech

Petty Officer 1st Class
Joined
Apr 26, 2012
Messages
386
Re: HELP ASAP PLEASE... 2nd hand Yamaha 50hp wont rev over 1700 rpm, should I buy it?

Do a leakdown test to determine health of the engine. If it is okay, then it is timing or fuel. It can be fixed....but at what price?
 

J@mes

Seaman Apprentice
Joined
Apr 11, 2012
Messages
49
Re: HELP ASAP PLEASE... 2nd hand Yamaha 50hp wont rev over 1700 rpm, should I buy it?

whats a leakdown test? how can I do it?
 

James R

Commander
Joined
Feb 1, 2007
Messages
2,678
Re: HELP ASAP PLEASE... 2nd hand Yamaha 50hp wont rev over 1700 rpm, should I buy it?

A compression test should tell you the story. RPM limiting could be a bad rectifier, Disconnect it and run the motor.
 

J@mes

Seaman Apprentice
Joined
Apr 11, 2012
Messages
49
Re: HELP ASAP PLEASE... 2nd hand Yamaha 50hp wont rev over 1700 rpm, should I buy it?

A compression test should tell you the story. RPM limiting could be a bad rectifier, Disconnect it and run the motor.

I don't have the tools to do a compression test unfortunately.

What do you mean by disconnect it and run the motor?

Thanks.
 

99yam40

Fleet Admiral
Joined
Sep 7, 2008
Messages
9,039
Re: HELP ASAP PLEASE... 2nd hand Yamaha 50hp wont rev over 1700 rpm, should I buy it?

You have no idea if it has bad pistons,rings,cylinders, carbs, fuel, CDI, etc.
Take it to a shop that can test if you can not do it yourself.
Get a survey done to make sure not only the motor but even the boat is in good shape.

Good chance it is only a fuel/carb issue, but you cannot be sure unless you test and inspect every thing that could be a problem.
And with a boat there are lots of things that can be a problem especially if it is a glass boat
 

Solittle

Fleet Admiral
Joined
Apr 28, 2002
Messages
7,518
Re: HELP ASAP PLEASE... 2nd hand Yamaha 50hp wont rev over 1700 rpm, should I buy it?

And forget everything that the seller tells you. His job is to get your $$ into his pocket. You have good advice here.
 

robaloroger

Petty Officer 2nd Class
Joined
Feb 16, 2010
Messages
123
Re: HELP ASAP PLEASE... 2nd hand Yamaha 50hp wont rev over 1700 rpm, should I buy it?

If the motor is only getting 1700rpms it has a problem. Might be minor or it might be major. Bad compression means you need a $2000+ rebuild. You can not buy it as a running motor. I dont know how much you paid for it but in my opinion a 2003 50hp yamaha in not running condition is only worth $500-$1000. I just bought a used digital tach for $100 2 weeks ago and it only reads 88 hours. If I put this gauge on a motor with 1000 then you would think it only has 88 hours. You need yamaha software to pull the hours on the motor. Dont believe a tach.
 

jhosea1979

Seaman Apprentice
Joined
Jun 16, 2010
Messages
47
Re: HELP ASAP PLEASE... 2nd hand Yamaha 50hp wont rev over 1700 rpm, should I buy it?

You can unhook a reg/rectifier and start the boat and run it to test the rectifier ??????
 

jhosea1979

Seaman Apprentice
Joined
Jun 16, 2010
Messages
47
Re: HELP ASAP PLEASE... 2nd hand Yamaha 50hp wont rev over 1700 rpm, should I buy it?

A compression test should tell you the story. RPM limiting could be a bad rectifier, Disconnect it and run the motor.
Would a bad ground on the rectifier cause voltage spikes if not what would ??
 
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