G8 randomly sputtering

kmbelt · 07-11-2018, 06:33 PM

My father-in-law picked up a 90 or 91 Yamaha G8 for $500. He has it running, but not reliably. He has done the following.

Changed oil
Changed spark plug
Changed fuel filter
Cleaned carb (no rebuild kit though)
Took apart and checked fuel pump
Replaced Coil
Generator is putting out good voltage.

Even after doing all this, it will randomly start sputtering, backfiring and running like a dog. After a while it'll be fine again. We assume it's an electrical issue and plan to check all wiring connections.

Any ideas are welcome. We hope it isn't the ignitor.

smallblock450sl · 07-11-2018, 07:02 PM

A dynamic spark test would be of good use on this. About 10 bucks at the auto parts store. Plug it onto the spark plug and the cap and run the car. When it starts sputtering, check for good spark. This will help isulate if it is spark problem. Did you use an NGK-BPR2ES spark plug? Was the coil OEM or aftermarket?

07-11-2018, 06:33 PM	#1
kmbelt Not Yet Wild Join Date: Jul 2018 Posts: 1	G8 randomly sputtering My father-in-law picked up a 90 or 91 Yamaha G8 for $500. He has it running, but not reliably. He has done the following. Changed oil Changed spark plug Changed fuel filter Cleaned carb (no rebuild kit though) Took apart and checked fuel pump Replaced Coil Generator is putting out good voltage. Even after doing all this, it will randomly start sputtering, backfiring and running like a dog. After a while it'll be fine again. We assume it's an electrical issue and plan to check all wiring connections. Any ideas are welcome. We hope it isn't the ignitor.
kmbelt Not Yet Wild Join Date: Jul 2018 Posts: 1

07-11-2018, 07:02 PM	#2
smallblock450sl Sometime's............ Join Date: Oct 2007 Location: Tacoma Washington Posts: 11,875	Re: G8 randomly sputtering A dynamic spark test would be of good use on this. About 10 bucks at the auto parts store. Plug it onto the spark plug and the cap and run the car. When it starts sputtering, check for good spark. This will help isulate if it is spark problem. Did you use an NGK-BPR2ES spark plug? Was the coil OEM or aftermarket?

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