Yamaha 9.9 FMH fuel ratio

[bala]

I've just bought a Yamaha 9.9 FMH 2004. It looks like a cracker but i haven't fired it over yet. Just got it today. I have asked the seller about the fuel ratio and he said 50:1. I had a look at it's manual online and that says 100:1 as does the sticker on the engine. I think there's a debate goes on about this issue. Does it just boil down to the owners preference? What are you guys/ girls thoughts on it?? Just to add; i also have a 4hp yamaha from 1982 and have always put the recommended 100:1 fuel mix in it. It's still going strong. Also, i'm going to do the 15hp conversion on the 9.9. ��

[willk]

Clearly the 'correct' answer is 100:1. That said, 50:1 won't hurt it. If you intend to run the engine hard all the time and not spend long periods idling, I would be inclined to continue with 50:1

Pack a spare set of plugs and a plug spanner in case of plug fouling which is possibly the only negative?

[Fenlander]

I have the 99.9% identical 15hp model, my second of this type. 100:1 is correct by the book. When running in they need 10hrs at 50:1 and those who have run in from new have had no problems with 50:1.

Chipko on here has both the same model Yamaha and a Chinese clone version. The clone version is advised at 50:1 and he also runs the Yamaha at 50:1 for fuel compatibility with no issues.

Last year I ran mine for some hours on a tank of fuel made up at 50:1 for my Tohatsu and it started /ran OK.

For my own choice I mix at 80:1 for outboards that are advised 100:1. I have a feeling, I don't think it's imagination, mine runs a fraction better on 80:1 than 50:1.

BTW are you aware you can convert yours to 15hp at no cost with a very simple mod?

[chipko]

Yes, all good advice above. As Mr F states we run our Yamaha 15 on 50:1 with no issues despite 100:1 being the manufacturers stated mix. We only do this as also run a Chinese Yam 15 clone and a Tohatsu 9.8 which are both recommended to run 50:1 mix, and logistically it’s much easier to run all three on the same tank/mix. The Yam tolerates the 50:1 mix just fine but have to say we run predominantly north of 4500 rpm so feel the richer mix probably beneficial long term.

[bala]

Thanks guys. I was just gonna ask if somewhere between the 2 ratios would be an idea. I'm gonna go with the 80:1. Sounds like the best of both worlds! Aye Fenlander, i watched a video on youtube about a year ago about the conversion and had been looking for the perfect 9.9 ever since; till now. The whole reason to getting the 9.9 was to convert. I've seen Blankton's thread on here as well. That's a cracker; straight forward and concise. I've got a new Excel Scout 420 and the engine. All i need now is a trailer. Been looking at Extreme trailers but my..........they're pricey!! I'm starting to get a pain in my chest.................around the wallet area!! �� I'll stick some pics on here when i sus out how to do it.

[Fenlander]

Glad you've seen Blankton's thread on the conversion. I'll link it below for anyone else reading the thread who's interested.

https://www.rib.net/forum/f36/from-9...oke-86461.html

[jonp]

I own the f15 two stroke Yamaha which is the same engine. According to the Yamaha mechanic I use, 25/1 for the 10hr run in period then 50/1 there on. While he said they can run at 100/1, this was just a way to get over the emissions regulations at the time before 2 strokes were banned from sales here. While they can run at 100/1, he advised not to as it would shorten the overall life of the engine. This 50/1 is echoed among everyone I know and all the research Ive personally put in.

At 50/1 I don't see smoke and Ive yet to see smoke or get fouled plugs even when idling in gear for hours. I do use a two stroke oil which claims to reduce any smowhich it certainly backs up on.