2 stroke 70hp loss of power

[Tantalus]

Have a 1999 2 stroke 70hp and when out today noticed got to 4000rpm and no more. Still sounds okay but just no power. Had visual check but nothing jumping out. Will try new plugs tomorrow (current only 2 months old). Up until today has been going well. Pumped primer also when underway to see if it was lacking fuel, no difference.

any ideas where I can start other than plugs? Appreciated

[ausnoelm]

You need to do at least the very basic trouble shooting, when you remove the plugs, have a look at them and see if they all look the same, check the spark when they're out, make sure the throttle is fully opening and go from there.

[DennisG01]

Has the boat been setting in the water? Bottom could be dirty.

[99yam40]

compression, spark, and timing are all easy to test
that is where most start
a spray bottle of fuel (pre mix if this is a C) so you can spray into the i

ndividual

carb throats while under way can help to see if there is a lack of fuel getting to a cylinder due to a plugging jet.

If a cylinder is running too lean it can hurt the piston/cylinder if you run it very long that way

[ausnoelm]

Any progress?

[pstephens46]

Any progress?

Dunno. But quite Tantalizing.

[robert graham]

I'd bet he's losing power on one cylinder because of a plugged carb jet or injector screen.....and need to fix it before a lean fuel condition fries a piston...

[ausnoelm]

Appears we will never know, seems like things are dying slowly.

[Tantalus]

Hey guy’s, sorry, had to head away and haven’t been on line to be able respond. Quite simply a 1 month old plug gave itself up. Working beautifully one day and stopped the next. What intrigued me would, start and idle no problem and up to 4000rpm no signs of any difference, but nothing beyond that, that’s where she fell short. $6 and back to life. Thanks for the input as always. Cheers.

[99yam40]

good to hear it was a simple fix.
spark plug failing at just higher RPM would be a hard one to find