Rough at lower revs

Hello all; I have a '99 that I rescued and have been riding for about 8 months now. It has a K&N filter, OEM pipe and a PCIII with the stock (not zero) map. It also has pretty new NGK iridium plugs.

The problem is that when compared to my '91 carbed VFR, the 800 is kinda rough below about 2000RPM, then as soon as it seems to get going, then it goes like a steam train. I installed the PCIII hoping to improve the engine smoothness (like it did on my other 2 bikes) and it definitely made a noticeable difference higher in the rev range, even the pipes are a healthy color.

I'm wondering if I have a mid-connected air hose somewhere. Does anybody have a simplified hose diagram somewhere?

Any thoughts would be highly appreciated.

Thanks!

 

Have you Sync'd the SV's ?


Check out below link on the UK VFR site on SV syncing: ( note need to register to see photos )

Poor @ low revs? = Starter Valves...a guide - Honda VFR Club

 

My 2000 did this too. Under acceleration below 4000, it did not have much power and was rough. Felt like a twin under 4K with a load. Up top, it felt fine. I found 2 of the spark plug caps on the end of the plug wires were electrically "open". These caps have a resistor and a long spring pressing that resistor against a contact inside. Corrosion and oxidation can make the contacts fail. I took the caps apart, tried to clean all the contacts and I was not successful. You can test yours with an Ohmmeter, end to end should be 5000 ohms. If you get an open, your cap is defective. The plug wires are just copper so they are just a few ohms. You can buy replacement spark plug caps 30700-MBG-000 for $23ea from Honda. I did not like the design, (I had 2 failed caps on a 10 year old bike) so I bought Magnecor wires and caps. These don't use resistors or springs, just resistor wire (carbon fiber looking center) and you need to screw on spark plug nuts on the threaded plug tip to grip the cable end (it is an automotive style end). This fix is basically converting to a automotive plug wire, except Magnecor has a 7mm resistor style cable and they have caps (our VFR800 uses caps about 4" long.) I got these from Steve Brown - Magnecor (Michigan, USA)
Telephone: 248-471-9505
Fax: 248-471-9506
WWW: MAGNECOR Race Wires: WELCOME TO MAGNECOR!

 

Thats how Honda tuned the engine, its a v4 don't run it under 3.5k revs unless in first gear!

 

It ran smooth at low speed when I bought it- then started running rough and chuffing at low speed under load. I found open plug wires- I replaced them with what I consider a better more reliable system than what honda used and I wrote it up. I doubt your fireblade feels that rough at low rpm. If your VFR does feel rough, you might want to fix it- it is NOT the way Honda built it. Mine is smooth now.