Why do oversized PV covers do what they do?

Bailey28 said:
For jetting changes, I tried the new cover with the stock setup, N1EF-1, 40 175. Not much improvement. I went leaner everywhere, then richer everywhere to get a feel for what the changes would run like, mostly changing the pilot and experimenting with different needles.



I could never get rid of the softening of response with the cover. The bike seemed to make a bit, and I mean a tiny bit more power at the very bottom end. Anything above that it just seemed less crisp. The power was there, but the sharpness was lacking some from the stock cover.



The cover was well made and looked great but it wasn't working for me in my situation. Without the cover I finally settled on a 42, NOZH-1, 160 main. I know the 160 looks lean but with the rich final taper of the NOZx series and the 95+ degree weather it rocks.
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I have just taken a flywheel weight off for similar reasons, it just feels vague at the bottom end. A bike with the weight and the cover would feel vague all the way through the range based on our perceptions. Not sure about proponents of these devices and how they ride but anything that reduces snap and crispness surely makes it more difficult to lift the wheel out if trouble? And I am not a racer, more a brisk trail rider.
 
I run a single 8mm spacer between the cylinder and stock powervalve cover. Seems to bump the bottom end a touch, without giving up too much of the snap.
 
I have a 10mm one to try this weekend.....i hope you are wrong in that it gives up none of the snap..... seems like these add ons would be better for people entering long distance trials, based on what people say.
 
I have the spacer fitted a while and like the extra torque and snap down low but I fell it takes a bit from the top end...
 
spooly said:
I have the spacer fitted a while and like the extra torque and snap down low but I fell it takes a bit from the top end...
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Odd that you felt that. I wonder if it could be in relation to something else?

When the PV is wide open the drums have rolled shut and the additional volume of the PV cases are no longer in effect. Its all just the exhaust port. Only when the drum valves are open (PV closed) should the extra volume be felt, and its effect is that of a longer/increased exhaust length.
 
Well that awnsers that.. it neither takes nor gives to the top.. maby the dents in my pipe have effected the top.. or possibly im getting to the top faster. . Or very possibly its all in my head lol
 
Maybe it seems that it takes away top end because having more bottom end and the same top end makes the power curve more linear so there is not as much of a "hit"?
 
Jakobi said:
Odd that you felt that. I wonder if it could be in relation to something else?

When the PV is wide open the drums have rolled shut and the additional volume of the PV cases are no longer in effect. Its all just the exhaust port. Only when the drum valves are open (PV closed) should the extra volume be felt, and its effect is that of a longer/increased exhaust length.
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Close but wrong if I can be an annoying winker. The effect is only to disrupt the returning wave to disrupt the positive effect turning up at the wrong time. So its not so much retuning as lessened effects of the pipe
 
(F5) said:
Close but wrong if I can be an annoying winker. The effect is only to disrupt the returning wave to disrupt the positive effect turning up at the wrong time. So its not so much retuning as lessened effects of the pipe
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Can you illustrate this for us? :D
 
Erm as in draw? Not really. I'm just saying that you are right in that the pv drum and gate are positioned to be effective when at high rpm but the drum opens up the chamber at low rpm to disrupt the return wave from doing harm. The additional volume of the pipe doesn't work to alter the speed of the wave for benefit if you see what I mean.
 
I hear you! But I like drawings..

So the extra volume actually results in? What is it that people are feeling? I haven't done any crude - big changes, back to back to gauge the over all effect of it alone.
 
OK so this thread has me wondering. Quick rundown of my bike. Ltr power valve cover, steahly 8oz. Fw weight, ltr jet kit and the head is milled. It is very much like an old farmall tractor in the woods. Tons of torque and will lug around in second and third gear all day. BUT it just seems flat from mid to top. Been considering ditching the flywheel weight. I bought the bike the way it is so Idk what it would be like. What's your thoughts?
 
The FWW is most likely NOT your problem. I have a very similar setup and it revs quick. All it did was give me some out of the corner grunt, not anything earth shattering but noticeable. Did not notice one bit on the acceleration. The steahly may be different since I got the GG/S3 or whatever Gofasters had for it.

I can tractor mine around, and yes the LTR cover, head mod, and FWW all add to that.
 
Do you have a Gnarly pipe on it or any FMF head pipe on it memphis.

Every GG I have ridden that signs off early had one.

Maybe the House of Horsepower is calling your name?
 
House of Horsepower!? It sounds awesome but what is it?

Also I have an FMF fatty pipe on it. And to make matters worse I had to switch to my Gnarly pipe temporarily until my fatty gets back from pacific for repairs. Keep in my mind prior to this bike I was on an 01 CR250 for 10 years and nothing revs and hits faster or harder than those motors so a lot of my complaint might just be ME!
 
Forgiven I would like to just buy your bike and not worry about mine. Lol got generate a little cash and convince the other half why I "need" it first though
 
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