1990 PROV 150 fouling plugs

[APbassn55]

Hey guys! I got a 1990 pro v 150 on a ranger bass boat I bought 3 months ago it has ran like a top! Until I started to noticed the other day it seem to be a little hard to start after being out on the water a while and normally fires right up after initial morning cold start . I went ahead and changed plugs same NKG BR8HS-10 at .040 gap same as it had. I also awhile ago changed from penzoil premium plus marine 2stroke oil (other guy ran it ) to good old yammalube 2m oil thinking I was doing the right thing. Well Multiple people have told me that yammalube is junk oil and that i should switch back to a synthetic blend type oil , I’m leaning towards Lucas. Anyways went out last week for a few hours no problems , went out this weekend ran fine all day noticed that my WOT dropped from 5500rpms to 5200rpms then I ended up fouling a couple plugs at the end of the day and limped back to the launch ramp running 4300 rpms Wot . Got home and pulled all plugs 4 were super wet oily and fouled . Wondering if i should ditch the yammalube and possibly switch to one series hotter of a plug to a 7 series ? Thoughts anyone? Oh and I cleaned plugs up with starter fluid and a brush and boat ran great after i got home.

[99yam40]

have you done any preventative mantanace?
posting the complete model # helps others know exactly what motor you have

[APbassn55]

Thinking that switching to yammalube and 91 octane and not running around lake at WOT , other then that no model number is PROV150D on the Yamaha stamp on the side.

[APbassn55]

And previous owner stated that he had carbs synced and oil mixer was replaced 6months ago

[TownsendsFJR1300]

And previous owner stated that he had carbs synced and oil mixer was replaced 6months ago

This should be your engine: http://www.boats.net/parts/search/Ya...UMP/parts.html

Per the picture, it appears there's an adjustment rod for the oil pump (part #20).

You may want to check your shop manual that the pump / pump rod is adjusted correctly.

You may very well be pumping too much oil in the engine (sounds like it)

I would NOT be changing to hotter spark plugs and use the recommended grade fuel.

I seriously doubt the Yamaha oil is the issue (once the pump is adjusted correctly) however the excess synthetic blend is probably running cleaner (and simply not fouling the plugs).