15 Hp Evinrude Problem

[Bay+Beyond]

Hi all,

My pride and joy has developed a small problem that has baffled both myself and some mechanics.

I have a 3.8m Stacer with a 1984 15Hp evinrude which before christmas was great, with 2 people in her she would cruise at 33Km/Hr. Bloody fantastic.

Now what is happening is that when i go by myself it runs fine, ie speed still gets 33-35km/hr, uses the normal amount of fuel, idels weel etc.,
But,

The problem arises when i put the second person (70Kg) in there. The motor still idles smooth and runs fine, but my speed drops back to 24-25Km/Hr. I don't end up using any more fuel, and the motor still runs smoothly.

This has me stumped.

I have changed spark plugs, looked at fuel filter/pump. The throttle arm opens right up. Have changed the fuel a couple of times.
I haven't looked at the carby yet, only because as i said earlier, it always runs smooth.

Last night i checked the compression, one cylinder 100 and the other 91.
The motor is getting on in years but even this wouldn't be the cause of lack of top speed! or would it?

What could the problem be??
It would be greatly appreciated if anyone in Ausfishland has any ideas of what might be causing this.

Cheers
Thommo

[2iar]

You haven't dinged the prop or changed trim positions/engine height since it was working fine have you? Or something simple like the fuel tank breather valve being (more) closed?

I'm not much of an expert, just thinking out loud...

Good luck,
Mike

[Bay+Beyond]

Mike,

Thanks for the suggestions, the more the better.

I haven't changed any trim/height positions or the breather cap etc. or dinged the prop

I did a little test one day and put new fuel in. Sat the missus up the front and off i went. As i expected only got to 24km/hr. so i changed the plugs out on the water, still the same, made no difference.
So i came home dropped her off at the ramp and headed back out straight away. didn't stop the engine.
Of course now with the lighter load got up to normal speed of 33km/hr.

Got me stumped.

Thanks
Cheers
Thommo

[finga64]

Could be something stuck in a jet or something funny in the carby.
Does it start easy just after a long hard run??
Only reason I ask this is maybe the crank seals are getting a tad old and need replacing. they let go real quick.
Or an obstruction in a reed valve. Compression is a tad down on the second cylinder as well

[ahoj]

If the motor is going flat stick with 2 people and doing 24 k and when only one person at full boar doing 34k it seems to me quite obvious that the motor is doing hard work and if you use only 75% ecceleration will not make any diff to the speed with 2 people.. conclusion: either the motor needs recon or the weight configuration is now other then you had last xmas. Make a comparison towing a boat or not.. consider taking few 4X out---- ;D ;D ;D


example: my cat has 6HP Yamaha and with one person runs @ up to 25 km/h with 2people it drops to 22 and over 75% exeleration has no further power with one person exeleration increases speed up to 95% I hope you can make some sense out of of this comment

If you nurcher your motor and don't overdo it it will be a good servant for long time yet..

Take it easy ---Ahoj

2iar your EX yammy is going great---- it is a good motor

Ahoj

[fishingbarry]

http://outboard-boat-motor-repair.com/Default.htm
Thommo,
I have used this site for info on an old Johnson I am working on, the guy that runs it is a dead set ledgend on Jono's and Evinrude motors,just go to the blogs section and post your problem.
Cheers and good luck
Barry

[Bay+Beyond]

Thanks Guys,

Finga,
Yeah the motor starts first/second time anytime, wether hot or cold.
it just seems to run so smooth, ie no coughing or farting.

Ahoj,
Want to nurse it along a bit, looks like some solo missions coming up.

Barry,
Thanks for the link. will look into it soon.

Thanks Guys for the responses.

Cheers
Thommo