Tech Tips

Two EFI Brain-teasers

Written by  October 31, 2003

Q: Last month I bought a used fuel-injected 2001 Harley Davidson Road King. This is the first bike I have ever owned that is fuel-injected and I have a question on how it works. The main reason for this question is that to check the mileage on my bike, I have to turn on the ignition, thus priming the cylinders. Does this affect the engine in any way if I do not actually start it afterward?
J.D., Overland Park, KS

A: Well J.D., great selection on your bike, as I too have the same bike! It’s not red is it? Anyway, I had that same question when I bought my 2001 Road King, as it was my first fuel-injected bike! The answer to your question is: When you turn on your ignition of your fuel-injected motorcycle, you do not “prime the cylinders,” as you put it; any sounds you hear are simply those of the electric fuel pump pressurizing the fuel system. The injectors do not squirt any fuel into the intake manifold until the starter button is depressed and the engine begins to turn over. So, you could switch the ignition on and off all day without ever starting the engine, and the worst thing that’s likely to happen is that sooner or later, the battery will go dead.

Q: I’m going to buy my buddy’s 2001 Honda RC51. I don’t have much experience owning a fuel-injected bike, and I am having a difficult time finding an answer to a question, in which I have gotten many varied answers. I am told that fuel-injected bikes do not require a choke/enricher, but it appears that the RC51 has the latter. Do I really need it?
Speed Demon - Jimmy H., Blue Springs, MO

A: Speed, with a name like that, it leads me to believe that you already bought the RC51, as Honda built that bike knowing that most riders would turn it into a race bike and thus have their fuel-injection programming altered. A manual cold-start system ensures that the engine will always start quickly and easily no matter how the engine or injection system might end up getting modified for competition. Sorry, I digressed from the answer to your question: Fuel-injected bikes do not need a manually operated choke or cold-start enricher. On MOST injection systems, the information provided by one or more of the system’s various sensors tells the engine-control module that the engine is cold, and the ECM automatically adjusts both the mixture and idle speed to compensate. On your bike, the system neither adjusts the mixture for cold starting nor raises idle speed; the rider must manually operate the “choke” lever. This opens two plunger valves that, like the enricher systems on many modern carburetors, pass enough additional fuel to allow the engine to start and idle at a higher rpm than usual.

A: OK, I know I will get a follow-up question from the BMW crowd, so I will answer it now. A BMW fuel-injected bike automatically adjusts the mixture for cold starts, but the rider must operate a manual lever to raise the idle speed during warm-up.

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