Flapper Mod Findings - Wrist Twisters
 
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post #1 of 14 Old 10-17-2008, 10:14 AM Thread Starter
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Flapper Mod Findings

Probably nothing that hasn't been said before but since there isn't a lot of posting today and I'm kinda bored...

I performed the flapper mod yesterday and after riding about 150 miles here is what I think of it...

Without dyno testing the bike before and after, I don't know if there are any full-throttle gains. However, that little place between accelerating and closed throttle that used to be very jumpy is now gone. Also, decelerating with the throttle totally closed is much smoother.

I never could get the flapper to 'flap' even while riding with the side covers off and looking at it, but feel that it more than likely mostly kicked in under heavy deceleration with little/no braking due to the high vacuum created then.

Since it smoothed out decelerating to the point that the low gear jitters are gone at stoplights, and slow moving jerkiness is gone...it's going to stay plugged. If you are questionable about it, just do it. It only took about 5-10 minutes total. Just undo it if you don't like it.

Probably nothing that hasn't been said before but since there isn't a lot of posting today and I'm kinda bored...

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post #2 of 14 Old 10-17-2008, 10:36 AM
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I had the same thought and compared back and forth. The first time I thought I had lost horsepower but, it really seems its just the jerky throttle response smoothed out.

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post #3 of 14 Old 10-17-2008, 11:26 AM
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I always thought the flap closed when the throttle was open and you passed a certain rpm. check out Wheeler's info on it at 919.org look in the mods section there's a link to Flapper mod. He never dyno'd it but he gives a little description of his "seat of the pants" impression.

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post #4 of 14 Old 10-17-2008, 01:43 PM Thread Starter
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I understand the flap closing at high RPM theory, but I always thought a car produced less vacuum the higher the RPM and the most vacuum when engine braking/decelerating. If it indeed did close at higher RPM, all it would do is starve the engine for air.

All I care is I like it better without it.

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post #5 of 14 Old 10-17-2008, 01:48 PM Thread Starter
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"Some cars built before the 1960s used manifold vacuum to drive windscreen wipers via a small piston and valve arrangement connected to the wiper mechanism. This system was simple and reliable, but meant that the speed of the wipers directly corresponds to engine speed. Also, under certain conditions (such as when the vehicle was climbing a hill at full throttle), little or no vacuum was generated and the wiper system would either stop all together or slow to the point of being unusable."

Little snippet from this...Wikipedia Link

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post #6 of 14 Old 10-17-2008, 02:50 PM
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Engine vacuum has to do with engine speed/throttle blade position ratio.Example at idle throttle blades closed 1000 rpm =ample vacuum. WOT engine speed 6000 RPM and climbing =no vacuum. The engine ia always trying to suck atmosphric gases when the trottle position is limiting the amount the engine can pull=vacuum. I hope this is clear enough. I ripped it all out flap door, and vacuum motor as it would create turbulance in the intake thus slowing the air flow

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post #7 of 14 Old 10-17-2008, 03:16 PM
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Quote:
Originally Posted by cmurphy84 View Post
"Some cars built before the 1960s used manifold vacuum to drive windscreen wipers via a small piston and valve arrangement connected to the wiper mechanism. This system was simple and reliable, but meant that the speed of the wipers directly corresponds to engine speed. Also, under certain conditions (such as when the vehicle was climbing a hill at full throttle), little or no vacuum was generated and the wiper system would either stop all together or slow to the point of being unusable."

Little snippet from this...Wikipedia Link
thats why my helmet wipers stopped the other night...lol...



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post #8 of 14 Old 10-17-2008, 03:57 PM
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When I went out of warrenty, I took the whole she bang out and put a patch over the hole left in the snorkel.
The position of the flapper at WOT is the same as it is when the motor is off,~ WO. When the motor idles the flapper shuts off half the snorkel, for a smooth idle, as speed increases, it gradually ( or should ) opens WO. It may affect drivability in a very cold climate, but, I never noticed a differance here in La.
Just like my choke~enrichner, I have never ever pulled it out.

[
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post #9 of 14 Old 10-17-2008, 05:48 PM
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Doing the flapper mod does not change in the cold. I have riden in well below freezing up here in the great white north. I would never undo the flapper. Is it unflapped now?

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post #10 of 14 Old 10-17-2008, 07:58 PM
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Quote:
Originally Posted by rickard919 View Post
Doing the flapper mod does not change in the cold. I have riden in well below freezing up here in the great white north. I would never undo the flapper. Is it unflapped now?
the flapper is vacuum actuated, so temperature of the bike and ambient temperatures have no effect on it.

I personally recommend it, even if riding in the cold as it smooths it out, the powerband feels more flat now, not a jump at 5500 or so anymore.

stock the flap closes half the intake beloew 4500 or 5500 rpm, above that under load it is open.

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post #11 of 14 Old 10-17-2008, 08:17 PM
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Flappers are mod!


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post #12 of 14 Old 10-17-2008, 09:06 PM
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Quote:
Originally Posted by sbeau1960 View Post
Flappers are mod!

ohhhh there are sooooooo many jokes..... mmmuussst connntroolll myselfff...





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post #13 of 14 Old 10-18-2008, 02:30 AM
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Until just a few days ago, I had the flapper 'modded'. I couldn't really decide on whether it made any/little/or NO difference, overall, at all. As quoted by others before, it seemed to flatten the power curve out,, but whether that flattening was because of a more even spread or actually taking away some power at certain revs, stayed a mystery to me - it just felt different than before, so I 'unflapper' modded it back to square one and I can now feel that same rush in the mid revs again. I have to admit,, I DO like that sudden power rush... It stays as per original unless I can find some technical reasons to re-mod it again...

I will watch this thread...

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post #14 of 14 Old 10-19-2008, 06:44 PM
8th bike and 2nd 919!
 
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dyno run would be nice

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