Thread: Fouling spark plugs

Hello. I had my VF with a 318 dyno tuned a few months ago and it ran great. last friday it was starting to sound a little rough and was harder to start in the morning and backfired that afternoon. I looked at the plugs yesterday and cylinder 1,2,3,4 plugs were fouled but 5,6,7,8 plugs looked good. From memory initial timing was set at 18 degrees and locked at 36 degrees total. The carby is a 650 ultra DP, the primary jets were changed from 62 to 65 as it was too lean. What could be the potential cause?

Thanks!

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Possibly a blocked idle air bleed on the primary side.