Loss of power

[brinky]

Help needed please.....

Had the boat out yesterday and today, I had the same problem both days.
The engine starts on the button, ticks over fine, I run it at about 4000rpm for 30 minutes then it looses power and won't reach 2000rpm.
Turn it off, starts again, still no power... Rev it in neutral it goes over 4000rpm. Out of the water on a hose pipe, revs over 4000rpm in gear !!!!
It's a selva 50hp 2 stroke.

Thanks for any advice....

[doggypaddle]

Revving it in neutral wont tell you anything, there's no load on the engine.
Try simple things first, is there a spark on all cylinders?

[brinky]

Yes, only two cylinders, sparking well and put new plugs in today just incase ...

[doggypaddle]

does it drop down to one cylinder when it wont rev?

[Peter_C]

How does it run after it has cooled for say 10 minutes? (Looking for overheating and the motor going into limp mode.)

Pull the spark plugs after and see how they look. Post a clear picture of them.

Did you try pumping the fuel bulb and see if anything changed?

[brinky]

Both days run for half an hour, then anchored for half an hour, 5 mins after restarting, limps home.
Will take a plug out and get some pics.
Had a new thermostat fitted lasted season.

[brinky]

Does sound and feel like one cylinder when it drops revs.

[brinky]

Yep pumped the fuel bulb, still felt firm.

[brinky]

Waited all year to get it out, then it don't work!!!!


The joys of boating.....

[paddlers]

Get used to it !!!!

[doggypaddle]

most likely cause i would think by the sound of it is an ignition component failing when hot.
I think if it was fuel related the symptoms would show up sooner?

[simsy]

Agree, coils are my bet...

[Peter_C]

Also pull the choke out and see if it runs better. If it does you can isolate cylinders with the choke feed by pinching them off one at a time, with a pair of pliers or whatever tool you want to use.

[brinky]

Thanks, I'll look into these tips and see what I find..

[Rokraider]

Fuel tank breather?

[Wee Dafty]

There is an overheat on the block, that shuts down one cylinder. Are you pumping water okay, may be the thermostat or the overheat component itself.

[brinky]

Pumping loads of water, had a new thermostat last season so hope that still works.
Will get a local guy to look at it...

[brinky]

This is a pic of a new plug after an hours use. Both plugs were the same ..

[Peter_C]

Plug color looks good. That light tan is about what you want to see on the center electrode.