To do the flapper mod look right in front of your gas tank and right below your instrument cluster. There will be a thing there that looks like a mushroom head with a tube coming out of the left side of it. Its the valve that open and closes the flapper. Pull that tube off and plug it up with a screw or something. It will just sit off to the side so dont worry about it. There you go. You just did the flapper mod.
The soft rev mod is alittle tougher cause you have to move around some wires on your ecu. All it does is remove the soft rev so you can run it up past 10K with out it hitting the rev limiter. I personally haven't done this mod cause I feel better with the rev limiter there cause I spent alot of money on my bike and I don't want to blow it up.
If you remove the flapper actuator (on top of the air duct), you can order a plate from TPO Parts to seal the hole.
It uses the spring steel plate from the actuator to snap into place.
As for the soft rev limiter, since my RC51 will not be raced, I've perfectly ok with the 9250 soft limit.
Revving higher will gain a bit more HP, but not worth the engine reliability.
Even then, the hard limit is 10.5K, so you only gain barely a 1000 revs for your effort.
As long as you've plugged any associated vacuum lines for the flapper to prevent leaks, the engine doesn't care.
The connector for the vacuum actuator is the round one at the top front of the left radiator for an SP2.
The squarish connector below it is for the left radiator fan so don't disconnect that one.
Mine was already removed and I just ordered a plate for the actuator mount hole from TPO parts to tidy it up a bit.
The whole flapper thing was to damp intake noise. I happen to like my intake noise
For the flapper, I used a little valve from a fish tank.
As for the soft rev limiter, Mike from rc51.org sent me one. Don't worry about motor issues, from what I understand, the US bikes were the only bikes with the soft rev limiter, everybody else got the regular hard rev limiter.
Directions on how to build one are on the rc51.org "free" mod page.
i too, heard the flapper removal was a must have mod for the rc. really had no idea what it entailed, just took it to my buddy's honda shop and said "do it". already running with a set of TBRs and and a pcIII. wow! i think my neighbors hate me now.
Yeah it's mostly plumbing and hardware.
Some leave the hardware in place and disconnect the solenoid and block the vacuum line. Others remove everything and plug the hole in the intake snorkel.
It was there only to damp intake noise.
It caused a big dip in power in the mid-range.
When the flapper valve closes, it blocks about 65% of the intake area. If you could locate a dyno chart of a stock bike, you should be able to view this.
How much I'm not exactly sure.
And this occurs around 5000-7000 RPM, and is responsible for some fueling issues around 6800 RPM.
The Basic Racer never had this since it was for intake noise control.
This via RC51.org http://www.rc51.org/valve.htm
You don't have to remove it, you can just disable it so it won't close.
Most remove the hardware to save weight and have a cleaner engine area.
If you disconnect the solenoid it will not open to allow vacuum through to actuate the flapper diaphragm.
I checked my bike for this and it appears it was already done. The hose was taken off, a screw put in it then with electrical tape taped backed in place basically on the flapper....if you plug the hose and it hangs loose does the old connection to the valve need to be closed?
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