I have a 2006 Heritage Classic, fuel injection. Recently, about one out of ten times, it will backfire when I start it, but will kick over. It does it hot or cold. is this a symptom of running lean? GThx.

 

Would like to know. My Superglide has done this a few times. Fires right up, runs great but every once in a while.....BANG!

 

Your IAC could be hanging up. Take off the air cleaner and switch the bike on without starting. You should see the IAC valve pop down into the throttle body (it may actually bob up and down a bit). You can try spraying some throttle body cleaner into the throttle body which can release a stuck IAC if that is your problem.

I don't think it would be other sources of lean or rich because it only happens some times and it only happens when you start up. It could also be timing but that would be consistent I would think. Make sure your air cleaner is clean. Notice if it is temperature sensitive. If it always happens when it is really warm out or really cold out then that could be mixture... I guess.

 

Thanks, man. I'll check that out.

 

What's an IAC? I took off my air cleaner and body on my fuel injected Heritage. The only part that moves is the throttle valve. It does not move when I turn on the ignition It is spring loaded. When I push on it, the handle bar throttle moves. It does the same thing if I move the handle bar throttle. it is not hung up. When I turn on the engine and rev it, the valve moves freely accordingly. It did not look dirty, but I sprayed some throttle cleaner inside anyway. I don't think this was the cause of the backfiring. Any other suggestions?

 

Ok. I found the "IAC." When I turn on the ignition, there is no movement, up or down. But when I switch if off, it slowly moves down. Is this the way it is suppossed to work? What does it do?

 

ok, making some progress now. In another thread, I read that IAC stands for idle air control. This appears to bypass the throttle butterfly. As I said in the previous note, mine only moves outward after I turn the ignition switch off.

 

The IAC sets the mixture and thereby the idle speed when the bike is being started and the computer tells it what mixture to use when the engine is at a particular temperature. There are a number of 'steps' that set the pintle extension distance based upon these conditions. If it is a little gummed up then it could be causing the variability that you are experiencing. I don't remember if you are using an aftermarket tuner but there are also settings in the ECM that have an effect on the IAC's steps and that's why I asked if you are experiencing this with a particular set of environmental conditions (same weather, variable engine temps, variable fuel source... variable everything... whatever). The IAC uses what is called a stepper motor to vary it's response if I'm not mistaken... at least that's how they work on cars.

There are a huge number of possibilities here. For example, your throttle cables could be hanging up on occasion. Have you ever shot some cable lube into them? If your air cleaner is dirty that could cause a rich condition. You could have the beginning of a clog in an injector. I would not want to have to chase this down until it got much worse and more predictable unless it is causing harm to the engine. Try to eliminate the variables. Buy your fuel from the same place with the same grade and the one that seems to get you the best mileage. Make note of the outdoor weather conditions. Make note of what you did before the backfire occured. (I mean, really, a note in a pocket note pad). It could be that your exhaust system or your intake system leaks air under certain conditions (always after a long ride for example). It could be that your battery voltage isn't consistent and you are losing fuel pressure on some days.

As for the IAC, it's no big deal to spray it with throttle body cleaner. When you take off the air cleaner, check to make sure that the throttle valve is completely closed. Turn on the key for two seconds and then turn it off while watching the pintle. Within 10 seconds the pintle should extend and then retract. If that is the case, do it again and blast it when it extends with the TB cleaner. (Don't start the bike right after using the cleaner... wait a few minutes.)

I always recommend, without asking, that anyone that wants to DYI on a Harley buys a complete set of HD manuals... shop, electrical, and parts specifically for your bike. It's an investment that can't be equaled. Every time I read one I see something I missed.

Without knowing how big a backfire you're dealing with, I can't predict if this is doing any harm... for that, you need to have it witnessed by someone that is an expert... and I recognize how difficult that may be. I spent a year each chasing two different problems. One was due to the characteristics of my exhaust system which I couldn't figure out how to solve and one was due to an ignition switch that was starting to fail. When the switch finally failed I was going along at 50 mph in traffic. At least it didn't fail when I was turning left in front of oncoming traffic. That's a good example of not really understanding how serious the problem could be.

Good luck.

C#

 

Thanks, that sheds some new light on this. I had the bike running today and placed my finger in the opening of the IAC, it had quite a bit of sucking pressure, and made the engine stumble. Also, now, when I shut off the igntion, the needle moves up and down a little bit and stays retracted. This tells me the whole thing is working right. I think I will remove the spark plugs next and see how they look. Thanks for all your input.

 

sorry, my bike has been backfiring and did a lot of things to check. Changed sensors redid fuel system. Now checked compression and both cylinders are at 140. By chance I checked the voltage at the battery and when I throttle it up the voltage goes bonkers. I check the voltage pretty regular due to the age of the bike and the voltage always stays close to 14 and doesn't bounce. Right now it goes from 13.5 to 9.6 and anywhere in between when I twist the throttle.

Any help would be appreciated.