Anyone else observed that the baggers seem to be sensitive to spark plug condition? I have a 2003 FLHTCi with 70,000 km on it and this is the 3rd year in a row that after winter storage the bike has vibrated and given erratic mileage until I replaced the spark plugs. As background, I do about 15,000 km a year, I fill up the gas tank before putting the bike to bed, I put in gas stabiliser and I put a tank of new gas in as soon as I can each spring when I start riding.

 

Nope. I've used stock HD, Champion, NGK and Autolite and not had an issue with any of them.

 

I have noticed on a few Harleys that I have messed with is sometimes they tend to run a little rough after storage. I think it the blow buy that gets into the air box and filter and tends to stick the idle pintal or throttle plate with storage. I personally run year round and if the evening is not below 35 and no ran /snow I will run mine to work and back (20 miles) plugs seem to last forever. However 15,000 km a year is 9321 miles to me. Air cool motors are hard on plugs. You have the fuel injection I think which is a little easier. However Harley recommends 10,000 mile replacement. If you run some a mixture of slow speeds which tend to crud up plugs and then some high speed runs plus tend to get a glaze on them causes misfire especially on a damp morning. If I was you and I had to put the bike up as long as you must since you say you use gas stabilizer (I park my mowers 3 months and I do not use anything other then a fuel up in spring) and I drove 15,000km I would just put in a new set of NGK 3932 DCPR7E plugs if that's what it takes to smooth it out. (Check the crossover number on the plug for correct requirement for your bike) Its probably what it needs.

 

My wife suddenly started complaining about seriously excessive fairing vibration on her 2007 Ultra at engine speeds between 1700 and 2500 RPM. I checked it out and she was correct. I checked all the brackets holding the fairing and found no problems. As a last resort, I changed the spark plugs and the problem went away and stayed gone. Last Saturday, I noticed a little excessive vibration in my 2008 RG fairing at the same engine speeds. I changed the plugs and no more problems. The plugs on my wife's bike were at about 24,000 miles (about 4000 past factory recommendation of 20,000 for a change) and my plugs were at about 11,000. Both sets of plugs indicated somewhat lean mixtures in both front and rear cylinders, but none of the plugs were overheated. Both bikes have FI.