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Discussion Starter · #1 ·
Ok I am not sure what happened but maybe someone can help.

So I am on my way to Laughlin, NV for the River Run in April from Portland, OR. I get about 700 miles from home, I just fill up at gas station, and I get a loud backfire (I nearly wet myself :eek:), then my rpm's shoot to over 2k. It sounds like it is missing in the rear cylinder not really missing but not firing right either.:dontknow:
After it backfired it won't throttle down correctly; it rev's down slowly so it is a little hard to shift from first through third gear, but I can ride freeway speeds with no problem. In first through third gear unless I accelerate hard it bucks a bit and stutters.

So I have Cobra shorts, FI2000R, and Sidewinder Intakes which I have been riding with since I had the bike at 650 miles and I have 10k now (had around 8k when it scared the hell of me). I rode another 2k miles to Laughlin and back hoping it would work itself out but unfortunately it did not. It does not seem to lack in horsepower at all but it just does not seem right either.

Oh yeah I was just messing around with the bike today and I was looking at the FI2000R and the yellow led does not light at all. So maybe this is my issue or maybe I have a bad coil pack not sure.

I am just wondering if anyone might have any idea what happened or how I may be able to fix this miss in the rear cylinder.

Short of taking it to a stealer I am hoping it can be fixed economically.

Thanks. :redfaced:
 

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2007 Candy Sonoma Red
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I'm assuming you don't have an FI light?

First thing I would do is check the injector connectors to see if one has partially came off.

Second would be the plugs, if you haven't changed them it's a good time to do so. It will run even if one plug goes out on a cylinder, but poorly. And it has to be the right plug going out as one fires all the time, and if that one goes out it will have a constant miss all the time until the 2nd plug is called on to fire. But since it runs under hard acceleration that's a likely cause too.

Next would be the fuel filter. Usually the first signs of them getting clogged is when the bike starts stalling at a stop, but not always.

Hope that gives you something to look at, and :welcome: to the forum. :D
 

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Discussion Starter · #3 ·
Thanks been viewing the forum for a while now and have had bike for 2 years and love it, but now I can't figure anything out :redfaced:.

So far I have checked both injectors (seem ok and seated), have changed both plugs, but still acts the same.

It does not so much run rough but you hear like air is being pumped out of rear exhaust like one of the plugs is not firing, of course I am not sure how the firing order is on the M109.

Will have to check fuel filter but I only get this on the rear cylinder and front is running like a champ.
 

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2007 Candy Sonoma Red
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It's an even fire engine, so you should get an even bang-bang-bang idle cadence from it.

I forgot to address the yellow light. That's for the middle pot, which adds fuel any time you are accelerating. If it stops working it could be leaning out, but it sounds like it's running OK under power. You can set the 3rd pot rich enough to compensate for it, but it's going to run rich all the time like that. The 3rd pot adds fuel across all rpm ranges.

If you pull the access cover off the box and watch the lights, the yellow light should come on when you hit the throttle, even sitting still. That shows it's active. Otherwise only the green light should be on. There have been a couple cases of the ground wire for these coming loose so you might want to check that too. It's easy to put back on if it is off, and I kind of recall the symptoms being similar to yours when it does. The ground wire runs out of the bottom of the unit and connects to ground.

Something you can check is the exhaust temps. It's best to do it with a infrared digital non-contact thermometer to be accurate, but in a pinch you can just touch the pipes. If the rear isn't firing, especially at idle, it's going to be a lot cooler than the front pipe.
 

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How did the plugs look? I would check to see if you are getting spark to the plug. A couple of people over the years have had that coil go bad.
 

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I think you're on the right track with the coil and I would check the connections at the coils (the standard style with a plug wire and the coil over) and see if the coils are firing. Since there are two spark plugs in each cylinder and two different coils per cylinder, the cylinder will fire just not quite right and it sounds like one fired at the wrong time. Just a thought.
 

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Air box is not seated properly. The reason for the backfire is still unknown, but what it more than likely did is unseat the airbox off the/a throttle body. Explains why it ran/runs since the backfire. Backfire could have been from bad fuel---you did just fill up right before. Backfire could also be from the fuel settings on the cobra---Zoom could better help you there on that set up. Check the airbox, bet you will see an issue. Also, check the rear center spark plug boot/coil (stick coil). Some where not pushed on all the way from the factory.
 
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