I bought an 2003 Ultra back in May. I did a scheduled mantenance on it a month or so ago and also replaced the spark plugs with standard HD plugs. The old ones were Autolite. My gas mileage seems to have dropped a few miles per gallon. Could it be the plugs? I'm in California so its not like I'm dealing with extreme tempertures changes from summer to winter. Any thoughts?

 

Don't know if they do it on the left coast, but here in jersey they use a different blend of gas in winter that usually will kill your mileage.,,

 

In N. Ca. and N. Nv there is ethanol in the gas beginning in Oct. to the start of Spring.
Probably true in Socal as well.
I notice a drop in mileage of 5-10%.

 

I hadn't thought of the change in gasoline during the winter months. I'm pretty sure they do that here in SoCal too.

Thanks for the input.