high/low spark?

[armybratsailor]

I have a Yamaha 115 2 stroke that has run like a top up until this past Memorial weekend when I noticed when advancing the throttle she would bog down. All I did was put new plugs in her to spec. She would run fine up to say 2600 rpm. After that she just boggs. My nieghbor said that a friend of his said it was the high spark not kicking in, thus too much fuel not enough fire. Is this pointing to the ignition coil? Any help greatly appreciated. Thanks, John

[robert graham]

Most likely a dirty carb or other fuel delivery issue. Next time it does it, pump your primer bulb, if it improves then a fuel pump or fuel restriction problem. If it gets worse, then mixture is too rich.

[armybratsailor]

First of. May I ask if this is Robert Graham, retired Army in SC? Just wondering. Yes, I was told it's running rich so after getting her back home I went out and got 98 octane fuel that I put in it straight up with no oil mix. Haven't gone into the carb but it it isn't a question of coil and spark then yes. That's my next step. Thank you for the reply. John

[armybratsailor]

Another note, she'll idle fine and run fine at low rpm. In neatral I can pull the rpms but under load is when she bogs.

[99yam40]

These motors are designed to run on 87 octane putting in 98 slower burning fuel is not a good idea.
If this is a premix motor why did you not add the oil like it requires? you will destroy the motor without oil.

When was the last time you cleaned the carbs? Sounds like that is what is needed.

If you think it is the spark then you need to have it tested or do it your self with the help of a manual and the proper test equipment

[armybratsailor]

high/low spark

I thought 98 octane would burn more. Maybe I had a rich mixture? mmm Good thought on that. I've only had the boat for three years and never did anything to the carbs motor etc. I changed plugs, water pump, fuel/water seperator. That's about it. I'm a novice for sure. Willing to learn though. Thanks for the heads up. I really thought higher octane fuel would burn quicker. What do I know? Not much! Thanks, John

[armybratsailor]

Running out to add oil to the two gallons of 98. And rocking the boat! I have a manual that sort of covers this motor but right equip.? Maybe not. Just trying to find a cost effective way of getting back to where she was. Thanks again.

[armybratsailor]

Spark/carb issues

Okay, I've just learned something new about octane ratings and I hope it's not going to be a hard lesson earned. As stated in the original thread, the engine bogs down only under load. In neutral it will rev which I've been told to be cautious doing so. I suppose I'll break out my manual which is a Clymer Yamaha Outboard Shop Manual. As far as special tools required I may be hard pressed. I failed to mention that the reason I at first didn't premix the two gallons was that it was burning rich so maybe my mix was off. I've been mixing at 50:1. This is a 1999 C115 TXRX V4. Perplexing as heck. Thanks for your reply's.

[99yam40]

As stated before clean the carbs and do the link and sync as the manual states.
Motor needs good gas and good oil 50;1 should be right
Good compression and spark and the correct fuel/air ratio to run properly