Random Idling issues

[mk2davis]

First, let me say that you guys have a fantastic source for information here. Everyone seems to me very informative and helpful.

I just bout my first FZR400 about 1 month ago, and it runs great when I'm moving, but has trouble keeping idle about 70% of the time. Usually she'll find a false idle at 2300 rpm, and then down to 1600rpm. Sometimes it'll slip down to 1200 and slowly die over the course of 30-45 seconds.

I just replaced the pilot jets (15) and the mains (100). The bike has K&N airpods and aftermarket exhaust from the previous owner, and was originally fitted with 114 main jets! Seems very rich to me, although the bike at the time was specifically a track bike. I don't know what else has been done to the bike.

I know the idle mixture screw should be set at 3.5 turns, but I know sometimes the factory sometimes plays with that setting. Where is the idle mixture screw on the 400, and does this sound like it could be the culprit? I don't want to start messing with something that won't fix the problem.

Thanks again for your help.

[rotortech]

mk2,

Just wondering why the pilot jets were changed and how was it running before that?

You may just be dealing with an air leak. Sometimes there can be air leaking in where the filters clamp to the carbs OR there is an air leak in the boots that connect the carbs to the engine. Spray starter fluid on these areas while idling. If the idle jumps up then you have an air leak at that spot.

Stock, unmolested carbs, have a metal plug over the idle mixture screw from the factory to make it tamper proof. I doubt that that plug will be there on a track bike. The idle mixture screw is in a cutout below the bowl. Here is a photo and more carb information: http://www.fzronline.com/wiki/doku.php? ... retor_page

Tell us why you did the pilot jets and what else you found in your carbs. That might help us help you.

[mk2davis]

When I first bought the bike, the idling issue was very sensative (sometimes not sounding like it was running on all four cylinders), and given the smallest throttle input would stall it out if not done carefully. I cleaned the existing pilot jet, and it not only sounded better, but held idle better, although the stalling issue with throttle was still present. Goosing the throttle after holding consistant hwy speed would cause hesitation, as well. Both of these issues let me to believe my mains were too big.

Sudco is about an hour away from me, and I figured if I am going to drive down there for new main jets (to help with the sensitive throttle), and new pilots would be better than trying to clean the old ones.

I'll see where the idle mixture screw is at for each of the carbs.

[sweekster]

Doesn't sound like these carbs have been synched or tuned-which in some cases is one in the same. I suggest having a carb synch session. You've already changed the jets so that next step can't hurt.

[rotortech]

+1 to what sweekster said. The previous owner may have just dropped these carbs on to sell the bike or never got it sorted out worth a damn. Read the carb thread, get a jet kit from Factory Pro and get it right. Doing a little at a time will just make you crazy anyway.

[mk2davis]

I read the page that was linked on the previous response. The pic showed the idle mixture screw in the bowl, but my manual (and my bike) has that screw underneath the plated diaphram cover. 1-3 were 2.25 turns out, and 4 was 2.5. Set these all to 3.5, and it seems to idle like champ!

I think your right, the next step is to sync the carbs, which I heard was a difficult endeavor with the pods. Is this not the case. Getting the factory airbox from England is going to be about $100 to get.