Air leak? Jetting problem? Cooling problem?

[OutRAGEous]

I bought this 61x 701 from the classifieds. The pistons look good when viewed through the exhaust ports. The water cooling passages had quite a bit of sandy debris fall out when I peeled off the shipping tape. Installed with stock 61x exhaust manifold and chamber.

I rebuilt the stock SBN 44 single carb. Jetting at the moment is:

135 main with high speed screw 2.5 turns out
120 pilot with low speed screw 2 turns out
1.5 needle and seat with 90 gram spring (pretty sure)

The carb was installed with brand new gaskets and dressing compound.

Here are the plugs after a day of use. This is from varying part throttle operation. The rear plug is much cleaner than the front plug....does this mean there's an air leak on the rear cylinder? Head gasket? Crank seal?

 

[OutRAGEous]

My father in law suggested that maybe the reeds for the rear cylinder are maybe chipped and not sealing well. Thoughts on that idea?

 

[Jakobi86]

Looks rich to me... I'd bet when that cleaner plug is seated in the head, the clean part of the porcelain is facing the intake ports. Fuel will wash them clean if it's too rich. How did it run? Was it stumbling or missing or did it have good power without hickups?


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[OutRAGEous]

Update here. I've ordered a bunch more parts from JetManiac, including new spark plug boots/connectors and different carb jets. My theory for now is the spark plugs aren't sparking evenly.

I will mark the plugs so I know the orientation in the cylinder and run the boat this weekend. I'll post some WOT plug chop photos too. I don't know if I have a problem or not but I was concerned about a possible air leak since I didn't test the motor before installation.

 

[Blue]

I agree. It looks to me that the one plugs not firing all the time. This is usually caused by bad coil wires and boots.

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[schicks]

I have had an msd make a plug tip half white and half black. I went down that same route of checking everything under the sun, including plug orientation. Check you cdi first, my plugs looked exactly like that.