Increase power on Yamaha 4hp 1999

[Norwegian Viking]

I have a 1999 Yamaha 4hp on a 9dingy that works very good. But I can not get it to plane except when I move forward, hence it is underpowered. My 10 year old son is using it in the lake and he feel a little stressed when the only thing he can see is the bow on fast forward.<br />Ive heard that the engine is the the same as a 5 hp. Is it possible to increase the power to 5 hp without spending a fortune on parts?<br />Thanks a lot!<br /><br />PM the NV

 

[jrod8v92ti]

Re: Increase power on Yamaha 4hp 1999

install a longer fuel supply hose and put the fuel tank and everything else you can in the very front of the boat.<br />ensure motor is centered and cavitation plate is even with the bottom of the boat.

 

[DJ]

Re: Increase power on Yamaha 4hp 1999

Ditto, jrod8v92ti.<br /><br />One HP is not going to make the difference. Weight distribution and and engine height/trim setting will/might.<br /><br />4 HP will not plane much, if anything. The same goes for five HP.

 

[Norwegian Viking]

Re: Increase power on Yamaha 4hp 1999

Thanks a lot for your tip! I totaly agree that 4 hp isnt much, but the boat is not more than 75 kg (150 ibs). The motor is centered and the trim setting is at its best. (done a lot of testing) The fuel tank is in the very front, so the bottom line is that if I want the boat to plane easier, I need to put on a bigger engine? So I did. Ive borrowed my brothers 5 hp yamaha, and what did I see. It was planing! I still had to lean forward in the process of planing but this time it stayed there. My son is less than half my weight, and therefor I have reason to belive that it will work for him too.<br />Back to the question... Is it possible?<br />All the best, PM the NV

 

[WillyBWright]

Re: Increase power on Yamaha 4hp 1999

Swap hoods and give your brother the 4Hp.

 

[Norwegian Viking]

Re: Increase power on Yamaha 4hp 1999

What a great idea!! Why didnt i think of that my self? Its only one little snag... Hed probably find out. Any other brilliant suggestions? <br />PM the NV

 

[ivar]

Re: Increase power on Yamaha 4hp 1999

There's 2 versions of the Yamaha 4 , a 83cc version and a 103cc version , which is the same as the 5hp.

 

[Anymec]

Re: Increase power on Yamaha 4hp 1999

What is the type of the 103cc 4hp Yamaha ??<br />I never heard about this 4hp before.

 

[Norwegian Viking]

Re: Increase power on Yamaha 4hp 1999

Ivar!<br />I dont know if it is a 83cc or a 103cc. How can I find out?<br /><br />Text in norwegian:<br />Ivar<br />Jeg har hørt at det er mulig å gjøre et eller annet med eksosen for å øke fra 4 til 5 hk.<br />Kjenner du til dette?<br /><br />Pål

 

[arrows_uk]

Re: Increase power on Yamaha 4hp 1999

Hi all, I also have a Yamaha 4hp (4 stroke) and was told that it was the same engine as the 5hp version so I am also wondering how it can be uprated to 5hp. My spec says that it is a 112cc verion. It's a 2000 year model or thereabouts.<br /><br />Rob

 

[Anymec]

Re: Increase power on Yamaha 4hp 1999

Originally posted by ivar:<br /> There's 2 versions of the Yamaha 4 , a 83cc version and a 103cc version , which is the same as the 5hp.

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[ida71]

Re: Increase power on Yamaha 4hp 1999

You could always add hydro foils to help lift the rear of the boat. I've used them on various engines over the years & they always worked for me !<br /><br />Chris W.