If the rear cyl failed to fire upon startup and you solved the problem by changing out a fouled plug. Guess what, it will happen again! A bike with a fouled plug setting for a couple weeks on a weak battery will show it's common practice of poor firing capabilities in the rear cyl.

Although the rear plug being fouled and producing a non-existant spark or at least a "weak" spark is a sign of carbon buildup caused by improper carb setup. Most Harley's are running this way due to the EPA restrictions imposed on the Harley factory.

Therefore, there will almost always be some plug fouling and the rear cyl seems to be more effected by it. Most of the time a good run on the bike will burn off excessive carbon build up and we all just keep chugging along. That's till winter time comes or the bike sets for spells at a time between startups.

Due to coldness, moisture and some fouling on the plug, a weak battery that doesn't produce a "strong" spark in a cold engine willbe the weakest link during a startup. The battery is suppose to provide engine spark (fire) for initial startingthen once running the bikes own ignition system keeps the spark coming! If there is not enough juice coming from the battery for the initial start due to a weak battery combined with a fouled plug... The engine may start on one cyl and the 2nd cyl may or may not come into play. Hence, gotta have a good strong battery esp in cold weather startups to assure plenty spark is avail.

You can clean your plugs and they may look good however the carbon down in the bottom of the electrode will weaken it's ability to properly spark so you may have 2 issues to deal with. Engine carberator settings and a weak battery. <------- Thoes 2 items may not seem to show any problems during warmer weather or daily riding but when the temp outside drops or the bike set awhile they will show their ugly heads..

 

Thanks for all that info...........Ill be sure to check all that stuff tom