Little off topic ,,but a motor is a motor Old Harley Sportster had sat a while,,new gas ran fine for about 200 miles,,now seems a lil sluggish,,like on 1 cylinder..Both are getting spark and new plugs,,and oddly the exhaust pip for the front cylinder does not get hot ( pipe is cold to touch ) Bad rings ?? Bad intake seal ?
That cyl isn't firing for some reason. Check the plug to see if it's fouled or the gap is closed. Also, I'm a complete idiot when it comes to bikes, but don't some old harleys fire both plugs at the same time like a waste spark setup? If so, you could be seeing spark at both plugs, but not necessarily on the compression stroke for the cold cyl. Not sure, just a guess...
if one pipe is not getting hot, then it's only running on one cylinder. Just because you have a spark at the plug when the plug is out of the engine does not mean that you have a spark under compression. Combustion produces heat- no heat no combustion. You could have a weak coil, bad plug wire or what I've seen is that the cam that triggers the contacts for that cylinder is wore out. Try making the sparkplug gap a lot smaller and see if it helps, if so then you probably have a weak coil or bad wires. Bad rings will not make a cylinder run cooler and an intake leak will, if anything make the pipe get even hotter because it's running so lean. I've seen exhaust headers on Harley's glow red hot from an intake leak. hope this helps
Cool thanks question ,, you say no spark under compression..why is that?? Is the spark so weak that the compression stroke snuffs it out ?
Compression makes it harder for the spark to jump the gap. And yes just half the coil can go bad, not too long ago I came across a guy on a sporty who was stranded at the auto parts store with the same issue. Luckily a biker buddy of mine lived around the corner and I ran and got him a spare coil.
This is what I see most often with those motors... You could also try to switch the wires on the coils, that would help to narrow it down.
When the air/fuel mixture is under compression and subjected to the heat of the engine it is much more dense and makes it harder for the spark to jump the gap.
no because both sparkplugs fire at the same time, just like someone earlier mentioned wasted spark, you can switch the wires all day long it will still run because it fires both plugs at the same time
I dont think so. My sporty has a single fire ignition, Fires both plugs at the same time. So theoretically it couldnt possibly be out of time if they both fire at the same time. If youre stll stumped jump over to the Jockey Journal. Its like HAMB for bikes.
What you have is a dual fire ignition because it fires both plugs at the same time, dually. A single fire system fires each plug separately, singly. All harley come with dual fire systems stock (except for the new fuel injected ones with the Delphi system).
Try putting in the old spark plugs. My OT Guzzi did the same thing a few years back. I could get it to run on either cylinder, but not both at the same time. Put the old plugs back in an it was cured.
The Jalopy Journal
