2004 F90 jet smokes on restart

[Skinnywater]

and has since new.
My daughters motor has 50 hrs. on it now and on a hot restart it smokes pretty badly. It's never overheated, runs fine otherwise, smokes only on a restart, and has always used Yamaha's 4stroke oil. The motor being a jetdrive almost never gets tilted.

My Honda when it was new did the same thing but never this badly and quit doing it after 20hrs or so. The level on the dipstick remains pretty consistant and doesn't indicate fuel contamination.

I'm thinking about switching to another recommended oil and checking for a difference.
I have the means to inspect with a borescope but I'm looking for known issues. It's unlikely we'll send it into the shop until after the season is over unless something changes for the worst.

 

[WillyBWright]

Re: 2004 F90 jet smokes on restart

That's a puzzler for sure. Most such problems are from lack of adequate break-in where the parts have not yet fully mated. The ones most likely to do that are babied motors that rarely see full RPMs such as on pontoons. But jet drives seem to be pushed to the limit more than propped versions.

In most cases, the problem is occasional. Not every startup. What happens is the oil that collects in the ring slots trickles down into the cylinder and burns up on start. Once that oil is burned, the smoking quickly stops. It can leak in via ring end gaps that happen to sit low in the cylinder, or past rings that aren't fully mated to the bores yet.

 

[Skinnywater]

Re: 2004 F90 jet smokes on restart

Thanks WillybW for the response.

I think 4 stroke marine engines are more sensitive to oil levels and tilting since they are mounted vertical, where with the horizontal automobile applications oil will naturally drain from the pistons/cylinders/rings.

Last weekend I lowered the oil level off the "MAX" mark an honest 12 oz (cup and a half) and the problem went away.