Backfire without starting bike - XJ11

[Prothec]

This morning I rolled my XJ out of the garage and down the driveway. When I got to the end I turned the key on and a moment later POW, I had a very loud backfire out the exhaust.

Before I rolled the bike I had turned the key on and switched to brights, then back just to see that the battery isn't extremely weak because I had charging issues recently before I swapped out my reg/rect and stator so I don't get to the end of the driveway and have to push it back up and I wouldn't want to wake up SWMBO by firing it up in the garage in the morning

My best bet is I'm set real rich (pretty sure I'm running quite rich right now) and had a decent amount of fuel sitting in the exhaust and the rolling of the bike built up enough static to discharge through a plug.

A little bit ago at work I rolled the bike around a bit and turned the key and got a good poof out the exhaust, again not touching the starter.

I've never seen this happen before.. anyone else have this happen?

[DAVINCI]

Kill juice to an ignition coil and what do you get?

SPARK.

That is simply how they work, my friend.

The TCI will shut down if it doesn't see any signal from the pickups. It does this to save the life of the coils. What you saw was the TCI shutting down.

Where the fuel came from, I can't say

[CatatonicBug]

Pretty common for me, but I don't have to roll the bike around first. Just turn the key, and I often get a quick pop. Usually not loud, but just enough to get my attention.

[Prothec]

Awesome! That puts my mind at ease. I always heard something in the past that almost sounded like compression releasing and that must be what it is. This time I had the ignition on for a minute before i shut the key off and rolled it out. That's the only reason i considered the rolling.

[bikerphil]

I have never had that happen in 20+ years.

[DAVINCI]

Phil, maybe yours is broke

[Rasputin]

I'm set real rich (pretty sure I'm running quite rich right now) and had a decent amount of fuel sitting in the exhaust and the rolling of the bike built up enough static to discharge through a plug.

Fuel sitting in the exhaust would seem to be indicative of a carb issue, where the fuel is flowing thru your motor while stopped. I think I would do a little looking around.

[bikerphil]

Phil, maybe yours is broke

Aw crap, not again. It's my voodoo electrics that prevents it.

[DGXSER]

I have to admit, I have never had any vehicle bike or cage backfire or sputter without having cranked on the starter at least.

I get what Randy is saying that the coil will charge when you turn the key on, and turning it off releases the charge and the magic juice goes out the wires to the plugs and makes a spark. But you would need some amount of compression in there, and fuel. So as has been suggested, you must have fuel leaking through carb floats, or a leaky float valve while running for enough fuel to still be there hours later, but still where is the compression coming from???

[Prothec]

Imagine my surprise when it happened.. It was loud enough to make me look behind me looking for someone holding a gun. I turned the key off, hopped off and took a look around the bike. It did start right up barely hitting the starter.

I will see what happens in the morning.

[WMarshy]

I have had this happen but only when I use the kill switch on the handle bars (have to return it to run) then turn the key off. It will ignite the unburnt fuel in a cylinder if the stroke and timing is just right... Ive never had a pop, usually nothing more than a good huff.

[Prothec]

I almost always kill the bike with the kill switch. I would usually hear a small huff near the carbs maybe 5 seconds after I turn the key. If this is just a stray discharge, I guess it makes sense it could either pop into the intake or the exhaust. It all depends on where the cams stop, which coil discharges, and the right fuel/air ratio.