How well (smoothly) does your F4 idle?
 

I've had my '00 since last fall. When I got it, it needed a little carb cleaning. Nothing major, but some cleaning. It idled very roughly, but ran very well otherwise. I cleaned them up, and the idle was a little better, but still stumbly. I cleaned them more thoroughly this spring, and the idle got better, but was still stumbly. I now live in the desert southwest, and bikes get emissions tested here. Having absolutely ZERO space here, I took the bike to a pro to let them go through the carbs (again) thoroughly. I have the bike back now, and...
...it still stumbles at idle. The guy said the carbs were clean. Maybe just a touch of varnish in the pilot circuit, but good. Valve clearances are right on spec. Compression and leak-down are right on spec and extremely even. Just got a UOA back on it and the numbers agree with what the shop is saying; namely, the engine is great. Still, the idle's stumbly.

So, how smoothly does your F4 idle? The only other F4 I've ever heard idle was an F4i, so not sure that really counts, but it didn't misfire even once.

hmm... mine is rock steady 1300-1400rpm...

check your idle screw

Define "stumbly".

W/a carb'd bike, you're going to have minor variation in rpm at idle.

Are you saying that w/ your idle set at 1300-1400, that it doesn't want to idle?
Or, are you saying that the idle just isn't constant/uniform at 1300-1400? And if so, how much variation?
Or other..?

The idle _speed_ is quite steady. Minor variation; not more than 100 rpm, usually less. However, it's misfiring (stumbling) noticeably. I don't mean it's running on 2 or 3 all the time, but it's clearly misfiring; not firing on all 4 each revolution. It sounds to me as if the misfiring cylinder is either moving around (seems pretty unlikely to me), or the misfiring cylinder(s) isn't misfiring every time.

If I slowly roll on the throttle from idle, it's not uncommon for me to be able to get a consistent misfire from one cylinder. IOW, I can clearly hear it running on 3. Under load, it evens out nicely and pulls like it should. I believe I had the pilot screws a touch too tight before, as there was the slightest hesitation during the transition from closed throttle to open. That's now gone, and I know the shop reset the pilot screws (and re-balanced the carbs, which were balanced, and checked the plugs, which were new, etc...).

I can't think of much to chase here. Maybe a vacuum leak, but I can't figure out where that would be.

The only thing I know of that's non-stock on this bike is the fact that one of the Direct Air Intake hoses was missing when I got it, as was the "T" that hooked that DAI hose into the DAI hose coming from the other side. I'll be looking around for one at a junkyard, but I have to be honest that the DAI system seems to me to be almost totally unlikely to have any impact on anything at idle. Has your experience been different?

I appreciate the feedback and help here. I'm not quite sure what to do. It may not be significant. My main reasons for wanting this corrected are:

1) Emissions testing here might get me on this,
2) More fuel is getting into the oil than it should (known via oil analysis; not horrible, but long term I want less fuel in the oil),
3) It bugs me. :)

I actually have a similar thing, the needle just slightly, like 100 rpm, but you can hear the change in the pitch of the engine noise.

is that normal?

Mine does it as well. Do you guys have aftermarket filters/exhaust? I'm thinking mine is that. I want to pull the carbs and see if the jets were ever changed. I think that might be part of my problem. Might is idling better after changing the r/r though. I'm going to upgrade the grounds and power wires here soon and see what that does. It's always helped out the idle on my civics.

Yep, normal.

I have a Yoshi exhaust.

Changed my R/R to the factory Honda upgraded finned version (very nice part) a few thousand miles back.

Any developments?

I almost asked at first about your vacuum hoses. Would be interested to know how it runs w/ the stock setup connected.

I had the upgraded honda finned one - didn't hold my voltage high enough. I had to go to the new mosfet r/r to get my voltages higher. Helped out tons. My bike used to barely idle if not die when the fan would kick on. Now it just has a slight miss every now and then. Very happy with it. Going to upgrade the wiring to see if I can get a bit more juice out of it. I'm holding 12.9v at idle with the cooling fan on.