Torque dip at 4500 rpm

Hey VFR World!

I got my first VFR, a blue 5th gen from 2001 with 38 000 km/23 600 miles, in the spring, and have since rode 6000 km/almost 4000 miles on it. Love it!

Something I've noticed is that when it is cold, there is a very noticeable torque dip at around 4500 rpm, so bad that if you accelerate moderately in first gear when just having started it, it jerks you forward at 4500 rpm, almost as if you let go of the throttle. When warmed up fully (not just up to coolant temp, but having ridden it a few minutes past that) it goes away and behaves reliably. This makes me think it sounds related to the wax unit?

I've tried to research this, but only thing I can find is it could be the starter valves needing synchronizing, but I really hope it could be something else, as that seems pretty complicated. I have read about the flapper valve mod, which I could try, but the flapper valve shouldn't be causing a problem.

Has anyone experienced the same thing?

 

Congrats on acquiring a VFR. Likely MAP sensor, clogged or fallen off vacuum lines making the MAP sensor not play properly. Above 4500 the ECU listens to TPS and rpm more than MAP. IAT possibly, fuel pressure regulator possibly, dumping too much fuel lower rpm. It should stink of unburnt fuel in this case. . Coolant temp sensor possibly, so ECU thinks engine is warm already when it isn't. Starter valves are all done by around 3000rpm, so it's not them. Wax unit is just fast idle, so not that either. Flapper mod, nope, when they fail they stay open. agood luck with it.