Hey guys,

Hopefully the title explains a bit of what I'm asking.

I've got an '07 Road King. I just replaced my stock air cleaner with the K&N equivalent to the Screamin' Eagle Stage 1 air cleaner (RK-3909-1). I also added Rinehart 4" pipes onto the stock headers. Here's where it gets complicated.

I replaced the rear Y-pipe header because it had cracked, so I'm a little that I may have left exhaust leaks because, if I'm honest, I'm not a particularly great mechanic. I couldn't feel/see/find anything, but that doesn't necessarily mean nothing is wrong.

After I put it all together I couldn't resist firing it up just to hear it. It sounds awesome, so now I'll trailer it to the shop for a remap and some tuning, all that good stuff.

Now, obviously I assume I must be running very lean, after freeing things up fairly considerably. So the popping didn't startle me, but I was surprised to see orange flames shooting out the tailpipe on decel (No load, just in neutral) after revving it up a bit. Isn't this the sign of a RICH mixture? Am I missing something, shouldn't I have a lean mixture?

What could I have screwed up here guys, can you help me out? Or at least put my mind at ease?

Thanks!

 

The "decel popping" and the flames are caused by the same thing. Un-burned fuel is exiting during the exhaust stroke. That fuel ignites when it comes in contact with the hot header pipe. Decel popping is normal. Stock bikes have decel popping but riders don't usually hear it until they put on less restrictive exhaust systems.

Basically what's happening is as you reduce the throttle to slow down, the throttle plates reduce the amount of air and fuel entering the combustion chamber. This creates a vacuum (reduced pressure). As the pressure reduces the air/fuel combination burns slower causing some fuel to be left over as the exhaust valve opens. As stated before, this causes fuel to enter the exhaust and ignite due to the heat of the pipe. The ignited fuel is what is causing the popping sound. This is also the cause of the flames. Stock Harley mufflers usually have spark arrestors that prevent flames from exiting out the end of the muffler. Performance mufflers to not have spark arrestors so you run the risk of flames exiting.

Get the new map for your current setup before you start trying anything else out. It will probably help with the flames, but just remember decel popping is normal and it's almost impossible to get it to go away completely.

Good Luck!

 

Thanks so much enodrano, you've given me some peace of mind!

Seems so counterintuitive to have unburnt fuel when I'm running lean to begin with, but your explanation makes sense. I'll wait to decide between a Power Commander or a Screamin Eagle tuner once the weather gets a bit warmer here.

Thanks again!

 

It's not really all unburnt fuel per se, as some of the exhaust gases are still combustible by themselves and that is what is reigniting.