Indexing spark plugs

[09benney]

I have an 09 Yamaha 50hp 2 stroke outboard that has run rough at idle up to 1800 rpms since the day I got it. Otherwise it runs perfectly. I went through the whole dealer service deal and at the end was told it's normal by a Yamaha service rep. His reason for the misfire was that it was set very lean to pass EPA and they could not by law change it. After the engine was out of warranty I adjusted the rich/lean myself and it had no affect on the idle.

I heard from a fisherman that runs Yamaha that you need to index the plugs to get it to run well at idle. So today I got 6 new plugs and marked the insulator at the side of the ground strap and kept trying plugs until I got all 3 cylinders to line up the exhaust side with the ground strap. Then I tested the engine, it was a vast improvement. It is a 3 cylinder engine, so it's not going to run like a v12, but it does not rattle the bimini top like it used to. I thought I would pass this on since I could not find anything on it when I did a search.

[captain rednut]

Thats interesting and thats the first i have heard of that however i can say that that model does miss on acceleration and comes good after a few seconds and i have never heard of a cure??.
cheers cr

[rodbolt17]

whatever it was it was NOT indexing the plugs.
the only outboards that require that are the direct injected E-tecs and old fichts.

none of the Yamaha motors have ever needed nor required plug indexing.

try another dealer, yes those carbs have tamper proof plugs over the A/F screws, yes we drill and remove them regularly.

[09benney]

Well the only thing different other than indexing was that the plugs were new. I checked the old ones coming out and they were indexed backwards. I have changed plugs before and it did not improve the idle. I know the standard procedure does not include indexing, it's just that it made a difference for me. It is not hard to do or expensive, so it was worth a try.

[BQUICK]

I'd be willing to give it a shot. I index my drag car plugs. Having the open side toward the intake charge should make a difference even in a 2 stroke. Top end could be better too.
Someimes I have noticed that idle was worse after installing new plugs. Maybe the old ones were accidently closer to being indexed.