Starts then dies repeatedly

[E350]

After riding for about 45 minutes today, the stock 701 61x would start then die. It did it repeatedly and my wife towed me in.

I immediately thought fuel starvation and will likely take the carburetor apart and check the fuel screen in the Mikuni SBN44.

But when I was checking the engine out on the beach, I noticed carbon on the spark plug terminal studs.

Has anybody seen this before? What causes it? Should I be concerned?

BTW, these photos were taken after I used my fingers to clean off the carbon. I then road only for a minute or so, and the carbon came back quickly.

 

[E350]

Well it wasn't fuel. I had 3/4 of a tank.

It wasn't compression. I just checked and have 160 psi in each cylinder.

It wasn't the coil wires. In fact, my wife's 1994 Super Jet has the same carbon on the spark plug terminal studs.

It was fuel starvation. There was about 3/16" of debris in the fuel filter in the carburetor.

Not anywhere totally obstructed but enough to cause a tow home at the end of a good day.

I replaced the gaskets etc. in the carburetor last night and today the ski performed flawlessly.

I had previously replaced the stock fuel/water separator (oem fuel filter) .

Now I want to add a fuel filter. What is a good fuel filter?

 

[Flash-FX]

The black stuff is normally from the aluminum cap wear on the top of the sparkplug. Those style plug caps are good for lawnmowers. You should probably be running resistor plugs with solid caps. NGK BR8HS solid (6715). Spray some cleaner in the plug boots and dry them out. Check out the connection. You might have to cut the wires back a little bit and re-install/replace the boots if they are damaged. A little di-electric silicone grease helps keep things going.

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[wydopen]

When you trim the wires back tug on the bare wire with some needle nose to make sure they arnt broken off further back in the insulation.

 

[mikidymac]

The OEM yamaha fuel filter/water separator is pretty hard to beat.

 

[E350]

@mikidymac I use the OEM Yamaha fuel filter/water separator but I added one of those little clear triangular filters to the fuel line right up near the fuel tank too.

The fuzzy stuff was incredibly coming from the air intake, past the check valve into the tank and was getting sucked up and caught in the filter inside the carb. I never would have thought that would happen! So I replaced that that OEM air intake line with fast flow fuel line too (blue).