It's funny you mention this Curt! just yesterday I was trying to find the dead cylinder on a 350 chevy and got bit pretty good...

Well if you got bit once it was a single fire and if you got bite twice it was a dual fire. If you banged your head on the hood it was a triple fire.

I think we're getting different definitions of what a dual fire system is. My definition is that the plug fires with each revolution of the crankshaft or twice as many times as it needs to (dual). In order to fire only on the compression stroke the system would need a camshaft position sensor in order for the computer to know when the piston was on the compression stroke and the Road Star doesn't. Your car does though. Because the bike has 2 coils it takes a load off of 1 coil trying to do it all and fires the wasted spark at a more precise time during the rotation. If one of our coils fails you might make it a short distance home with a bad miss which is not the case on a system with a single coil.

Also, it would be overly complicated to run 4 spark plug wires out of 1 coil.

Scott B.

i know the 2002 is single,i had to set my valves on tuesday when i finished my rebuild.(also the pushrods go back to back front to front on the rear cyclinder and back to front front to back on the front cyclinder)

I'm confused now also. I've tried to work this out and came up with a comparison between the Harley and the Road Star.

Starting with the rear #1 cylinder the Harley triggers the coil and fires on the compression stroke with a wasted spark going to the front cylinder. 405 degrees later the coil is triggered again and the front cylinder fires with a wasted spark to the rear cylinder. 315 degrees later the coil is triggered again for the rear cylinder. That's 3 signals in 720 degrees.

I've read that this off time wasted spark is part of the Harley sound.

On the Road Star I'll use the rear #1 cylinder. On the compression stroke the coil is triggered and the plug fires. 360 degrees later the coil is triggered again and a wasted spark is sent to the exhaust stroke. 360 degrees after that the coil is triggered again and the cylinder fires again. As with the Harley that's 3 signals in 720 degrees. So, if the tach is hooked to that coil it's getting the same number of signals as the Harley.

Depending on how the igniter is wired internally it might even be possible to hook things up so the Road Star would work with a single coil.

Would someone please show me the error in my thinking. I'd really like to know what I'm missing.

Scott B.

I think your reasoning is sound texasscott, my only question is does the r* fire the wasted spark? In todays world the signal being generated once every 360 doesn't mean that both coils get energized at the same time, I figure the ECM chooses which coil gets the signal.. I don't see the purpose for putting 2 coils in a bike if you run a dual fire ignition..like you said in your first/previous post, they did it cause it was simple back when the signal was generated with ignition points, now days with all the electronics it seems as tho it would be just as easy to do the single fire..In the old days, they used to have dual point setups that would change a dual fire to single fire...

And thats all I know about that...and still didn't come up with a definitive answer....

But I can promise ya that old 350 was triple fire....

texasscott1 wrote:
I'm confused now also. I've tried to work this out and came up with a comparison between the Harley and the Road Star.

Starting with the rear #1 cylinder the Harley triggers the coil and fires on the compression stroke with a wasted spark going to the front cylinder. 405 degrees later the coil is triggered again and the front cylinder fires with a wasted spark to the rear cylinder. 315 degrees later the coil is triggered again for the rear cylinder. That's 3 signals in 720 degrees.

I've read that this off time wasted spark is part of the Harley sound.

On the Road Star I'll use the rear #1 cylinder. On the compression stroke the coil is triggered and the plug fires. 360 degrees later the coil is triggered again and a wasted spark is sent to the exhaust stroke. 360 degrees after that the coil is triggered again and the cylinder fires again. As with the Harley that's 3 signals in 720 degrees. So, if the tach is hooked to that coil it's getting the same number of signals as the Harley.

Depending on how the igniter is wired internally it might even be possible to hook things up so the Road Star would work with a single coil.

Would someone please show me the error in my thinking. I'd really like to know what I'm missing.

Scott B.

IMO you've got the cycle theory correct, just don't count the last spark on the same cyliner you started with. The third spark your counting is the beginning of another full cycle.
So Harley's would have 2 pulses per 2 crank revolutions.
I don't think our coils fire on the exhaust stroke, just the compression stroke. For ours, a coil would produce 1 pulse per 2 crank revolutions. I guess I need to test this per Curt's instruction. Defibrillator?

This started over buying a tach for the Roadie! I ordered the one for the dual fire, and it hooked right up and works fine....Butch

Agpilot wrote:
This started over buying a tach for the Roadie! I ordered the one for the dual fire, and it hooked right up and works fine....Butch

This is all I really wanted to know I guess, which tach to order, thanx Ag