Were the spark plugs black (sooty)? and had the oil level dropped?
Forgot to mention the outcome: the engine was running too lean on the lower third of the rev range, thus when pottering about at low revs the engine was getting too hot, fine if you thrashed it though, dynojet sorted out the fuel flow and it never suffered from that problem again.
Aparantly when the Harley engine gets too hot the rear cylinder (which on a Harley would be the hottest)only fire every alternate cycle, if it is still too hot it somehow allows oil into the cylinder bore to help cool it down, thus the sooty plugs.
Last edited by exbiker; 10/12/15 09:17 AM.
