Yamaha mariner help

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Redhawk

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Hi. I’ve just bought a Yamaha mariner 15hp 2 stroke. The identity tag is stamped with a k which I am told dates the engine at 1985. Could anyone advise on the fuel ratio, she’s a good runner but smokes a bit, I put 50/1 in but some say it’s 100/1 on this engine. Some say to go in between around 75/1 ??? The plugs are slightly sooted up so advice on which replacement plug to put in would be great aswell. Many thanks.
 
Redhawk said:
Hi. I’ve just bought a Yamaha mariner 15hp 2 stroke. The identity tag is stamped with a k which I am told dates the engine at 1985. Could anyone advise on the fuel ratio, she’s a good runner but smokes a bit, I put 50/1 in but some say it’s 100/1 on this engine. Some say to go in between around 75/1 ??? The plugs are slightly sooted up so advice on which replacement plug to put in would be great aswell. Many thanks.
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Here is a bit on Serial Numbers

Yamaha Outboard Serial Number Location and Model Identification | PerfProTech.com

I'd be a bit surprised if the mix ratio was100/1 back in 1985 (I could be wrong)
 
Redhawk said:
Hi. I’ve just bought a Yamaha mariner 15hp 2 stroke. The identity tag is stamped with a k which I am told dates the engine at 1985. Could anyone advise on the fuel ratio, she’s a good runner but smokes a bit, I put 50/1 in but some say it’s 100/1 on this engine. Some say to go in between around 75/1 ??? The plugs are slightly sooted up so advice on which replacement plug to put in would be great aswell. Many thanks.
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Back in 1985 100:1 was becoming fashionable.. Yamaha where probably the leaders in this fashion. . I dont think Mariner badged Yamahas followed this fashion

The Mariner manuals I can find specify 50:1. The Yamaha manuals I can find specify 100:1

Run it on 50:1
 
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These old yamaha engines were 100-1 advised back in the day and years after that too. Ive a couple of 8hp and a Malta too. All advised 100-1. I mix 50-1 though. Many still mix 100-1 without issue to be fair. I prefer to be a little cautious. For the sake of a couple of spark plugs per year at around £6 in cost !
 
Redhawk said:
Hi. I’ve just bought a Yamaha mariner 15hp 2 stroke. The identity tag is stamped with a k which I am told dates the engine at 1985. Could anyone advise on the fuel ratio, she’s a good runner but smokes a bit, I put 50/1 in but some say it’s 100/1 on this engine. Some say to go in between around 75/1 ??? The plugs are slightly sooted up so advice on which replacement plug to put in would be great aswell. Many thanks.
Click to expand...

Is it badged "Mariner" or " Yamaha"?
If it is a Mariner what is the full serial number?

If it is an '85 Yamaha the plugs should be NGK B7HS-10

Compared with the plugs in Fantasie's link these do not have a projected insulator (P), are 1 grade hotter ( 7 vs 8) and are gapped at 1.0mm rather than 1.5mm ( -10 vs -15)

What spark plugs are fitted at the moment
 
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