1992 Yamaha C40 rough idle

[Boat_Boy!]

Hey guys,<br /><br />My C40 runs great out of idle but like a bag of hammers at trolling speeds. I'm new at this, so be gentle.<br /><br />The fuel mix is 100:1, running good, fresh gas, high quality oil, fuel filter is clean. This engine has not been run in about three years, but started right up on the first turn of the key. Where should I start?<br /><br /><br />------------------<br />Boat_Boy!

 

[Fouled Plug]

Re: 1992 Yamaha C40 rough idle

Did your replace the spark plugs? Might help a bit. But if I remember correctly, those C motors are "commercial" models and aren't known for their butter-smooth idle. Might think about a trolling plate so you can idle it up a bit and still fish, but I'd suggest a "kicker" if the budget allows.

 

[Bear]

Re: 1992 Yamaha C40 rough idle

Does it idle worse today than three years ago?<br />Cleaning carbs might help.<br />And new plugs.

 

[Swamper]

Re: 1992 Yamaha C40 rough idle

Fouled Plug what do you mean by commerical models?

 

[Boat_Boy!]

Re: 1992 Yamaha C40 rough idle

Hey guys, I cleaned and re-gapped the plugs before I started it. The engine was inherited, and I don't know how it ran 3 years ago. It was my grandfather's boat/motor.<br /><br />I have an electric kicker, but I need to know if I should use a regular car battery or a deep cycle. My understanding is that the car battery will provide better starting reliability but the deep cycle will last longer for the kicker. Anything to add?<br /><br />I don't know anything about commercial motors, and I will try a new set of plugs this weekend.<br /><br />Thanks,<br /><br />------------------<br />Boat_Boy!

 

[Fouled Plug]

Re: 1992 Yamaha C40 rough idle

Yamaha's C models are premix motors as opposed to oil injected, and the local dealer sells them as "Commercial" models. Just a few less bells and whistles, I guess.<br /><br />------------------<br />Fish on! FISH ON! Holy cr*p, it's a whopper! Oh boy Oh boy! Oh, wait... It's just kelp.

 

[Fouled Plug]

Re: 1992 Yamaha C40 rough idle

I almost forgot, the new Yammy C40 runs a 50:1 ratio. Even if the manual recommends 100:1 for yours, may not hurt to add a bit more oil.

 

[12Footer]

Re: 1992 Yamaha C40 rough idle

Fouled plug is right. The correct ratio is 50:1 ,or 3oz to 1 gallon.<br />No wonder it is clackin.

 

[Boat_Boy!]

Re: 1992 Yamaha C40 rough idle

Okay, but I thought adding more oil would make it more susceptable to fouling the plugs at idle. Since the motor had not been run in so long, the actual mixture I am running is 80:1. I figured a little more oil couldn't hurt after sitting so long. I am Canadian so ounces and gallons mean diddly to me... the mixture is 150mL to 12L. BTW I am using 89 octane unleadded and not "marked" gas... I could not find any nearby.<br /><br />------------------<br />Boat_Boy!

 

[sockeyerun]

Re: 1992 Yamaha C40 rough idle

Hi, Sounds to me like your carbs need to be cleaned. Unless all gas was removed from your carbs before your motor was stored(lines,filter,bowls, etc.)this gas evaporates and leaves a residue called shilac that will clog the idle circuts,jets,etc.. I have a 1993 Yamaha 40 that started idling poorly and would die sometimes in the middle of backtrolling,no fun.Took it to the dealer and you know the rest. Works like a charm.Fuel stabilizer is a must and completely draining your fuel system before putting up for any extended time. Goodluck

 

[Bear]

Re: 1992 Yamaha C40 rough idle

Oilratio 50:1 is like 2% in Sweden, or 0,2L oil for 10L of gas, 0,3L for 15L and 0,4L for 20L. But I guess you know about Liters n stuff.<br />I also agree to sockeyerun...<br /><br />Bjorn<br />Sweden