I have an '02 VTEC bike - and a little question about fueling. I notice a bit of a "hiccup" effect occasionally between 4000-5000 rpm. It acts like I just momentarily closed, then opened the throttle. At first I thought it was just me -- maybe I was a little "jerky" with my throttle hand. But then while browsing one of the British VFR forums, I found there were many people discussing a similar problem. It isn't anything major -- just a bit of an irritation. And it doesn't even happen all the time -- just once in a while while cruising (but always between 4000-5000 rpm). I wondered if others were noticing something similar in their bikes on this side of the Atlantic. Also -- some of the people on the British forum mentioned that they solved the problem by installing K&N air filters, and maybe O2 eliminators. I checked the K&N website, and they don't list an air filter for the '02 VTEC bike. So what gives? Do they have something there that we don't have over here? (by the way, I posted this question elsewhere as a reply to another fueling question - but I just got registered on the forum and thought I'd post it as a new thread.)
Very lengthy reply follows. First off you are not imagining the “hiccup.” It’s there; it’s also on almost all other fuel injected sport oriented motorcycles. Welcome to the world of fuel injection and federal regulations. I can duplicate the "hiccup" easily with just a slight movement of the throttle hand. I don't experience it on a regular basis though, mostly over rough pavement. The reason this happens is no real defect but can be considered and artifact. Manufacturers are tested for emissions and sound level at several rpms but the one that really counts is between 4000 - 5000 rpms. So manufacturers have for years leaned out their bikes and designed air boxes and exhausts to muffle their bikes to get through this test. Now add in fuel injection, if you've read any magazine tests they have been noting for a while the light switch response of fuel injected motorcycles. As to cures, I wouldn’t know why a K&N would have any effect as the fuel injection system will learn to lean it back out to factory settings. Anyway, by flowing more air you are creating a lean condition, that’s why you used to have to change carb jetting. Now O2 eliminators do have an effect in the rpm range and eliminating them could very well reduce the effect of changes in throttle as their purpose is to lean the mix out as much as possible without damaging the engine: just to get through the testing with flying colors. If you’re still interested here are some more things to think of on the subject. The lighter the reciprocating mass the more quickly the engine will gain speed and new to most of us, lose speed. Carburetors had a good deal of overlap when decreasing throttle, fuel injection doesn't. When the system senses a closing throttle, particularly in the 4000-5000 rpm range it immediately reduces the fuel. Add in very little rotating mass effect as in a 2002 V-TEC and you have, with very slight throttle movement, a decrease in engine rpm but little decrease in speed. You then correct for it and wonder what the heck was that. Now if you ride a large sporting V-twin as well, you get to experience serious engine breaking when you close the throttle if there’s no flywheel mass. That can be really unsettling. Are manufacturers doing something about this? Yes and no, they still need to pass the required tests but they are beginning to add slop into throttle closings. Suzuki has gone so far as to create a secondary throttle circuit to help eliminate the effect on certain v-twins. Basically Suzuki is mimicking a CV carb with electric circuitry. If you’re still reading, you may be asking why I don’t have the momentary throttle “hiccup” as much as others. Don’t know to tell you the truth. Only thing I can think of is I keep a very light throttle hand barely touching the grip.
bicycle66 , What did you ever make of the problem, I have a similar one that I just posted. The dealer cannot replicate the problem because he would have to keep the bike for a few weeks . 03 vfr non-abs . Sincerely, James
My stock '02 VFR had the same problem. I installed Staintunes and a K & N filter and it just made the "surging" worse. As others have mentioned, the bike is running very lean from the factory, and adding a less-restrictive exhaust and intake filter just made this matter more pronounced. However, once I installed a Power Commander, the surging/hesitation disappeared, presumably due to a more ideal air/fuel mixture.
