Hi Dave, some info you may be interested in. I’ve recently bought an ’02 VTEC as my daily commuter, after using a BMW R1100S. My VFR doesn’t run badly, and personally I like the VTEC transition. Really the only issues I’ve had are a flat spot between 3.5K and 5.5K rpm where the motor vibes a bit and struggles slightly, an occasional surging when throttling on from low revs, although that’s easily avoided, and fuel economy not being as good as I’d expected. Oddly enough, the harder I ride, the better the fuel economy, so I suspect something is slightly amiss.

Anyway, I’ve not found any concrete info regarding disabling the flapper valve, so I decided to have a go myself while checking the air filter. I had previously bought a bag of little plastic inline air valves so I could leave hoses attached to the inlet vacuum spigots on my CBR for synching the carbs (they’re a bitch to get to, so this saves time at each service). Using an extra length of hose on the flapper actuator, the air valve is sitting just beside the fuel tank, and I can enable and disable the flapper at will.

So far after about 100 miles or so, what I’ve found doesn’t fit the perceived wisdom. Most info I’ve found indicates that the flapper should only make a difference at large throttle openings. With mine disabled, it definitely makes a difference to smoothness at low throttle openings, perhaps a little less throttle snatch, but doesn’t feel like it’s added any bottom end grunt. It certainly hasn’t solved my flat spot anyway. When the motor gets hot, having the flapper disabled seems to cause a frequent surge at around 5000 rpm at low throttle openings. The revs rise to 5000, then the motor seems to “hang” for a moment until I add a little more throttle, then it passes it OK. Very weird, and it doesn’t happen every time.

I’ll do some more riding and test further. I can see at the very least a new air filter, and possibly a Power Commander in my future.

Oh and nice bike, and nice mods by the way!