F4i Sputter
 

Hey everyone,

I have 2002 Honda F4i owner since 2004 30,000 miles. Bike mods, PC3 (had custom tune however, it was at high elevation now I'm at sea-level) So I am currently running Pc3 canned tune stock exhaust / stock air filter. I have M4 high mount slip on, APE manual CCT, +1 front/stock rear sprockets. Recent FPR replacement and Spark plugs (stock).

My bike has always had a sputter especially between 3-4k rpm, but now I have developed in the past year an off throttle sputter, pops and crackles very fast sounding from 9k-5k rpm. This is with throttle off decelerating. The bike starts just fine initially @ 3k, and at temp it idles 1300 +/- 100. I have tried multiple gas stations (non-ethanol, ethanol, 87, 89, 93) 93 offer the best throttle response. I have put sea foam in gas tank a while back, I have tried stabil, Pulled the plugs to check gap. I have not had valves adjusted in my ownership nor have any hoses been changed. The had a lot of garage time from 2008-2013 with minimal riding. The gas mileage varies, from what everyone says I am average, but I used to avg 45-50 mpg with this (hand calculated, with higher gearing which has my speedometer accurate within 1mph. Now I am getting 35-40mpg. I drive 90/10 highway/city average 65-80 mph on interstate.

The exhaust smells rich. I'm at a loss as to what is going on. I can deal with gas mileage issue, but that sputter is driving me crazy. About a year ago when I was developing this issue, I discovered a marble, yes a marble, in the Large vacuum line coming off the back side of the airbox. How it got there is beyond me because a marble does not fit through the nipple those connects to. I removed it, with no real improvement. I was not sure if it was used when I had a custom tune placed on bike years ago.

Hope I gave some decent details of my situation. Any input would help!

Thanks in advance

Someone put the marble there to block airflow, why I'm not sure. Has the PAIR mod been done? If there are block off plates on the cylinder head cover then the answer is yes, perhaps the marble had something to do with that?
The PC is wasted on your setup besides throttle mapping, which requires the custom tune you don't have anymore, so disconnect it and eliminate that as a possibility first. I hear about PC's causing issues all the time on trackbikes. Poor running at only certain rpm's makes me think air/fuel ratio as well.

From a quick glance, it does not appear to have the PAIR mod. I had never heard of the mod prior to your post, but based on the placement of this marble, it would be mod of some nature to eliminate the popping from the PC.

It blows my mind when people who have had custom tuning done have never been told by the dyno operator about the PAIR removal mod. Its required to tune correctly. Pair is just an emissions thing.