i switched out my old UNI silencer that was packed full and has about a 2"x1" big hole in the midpipe.i put a good FMF powercore.first thing i noticed was it was ALOT quieter.it sounds so much better.then i took it out for a ride and it seemed like it didnt hit the powerband as hard.just seemed like it had "easier" power.i dont know if it is just because i cant really hear it hit it as good or what.what do you guys think?also after it was completely warmed up and it was in neutral ideling and you would punch the throttle hard it would bog a little then pick up like normal.it dosnt do this in gear.the plug looks fine.i have a 68 pilot/slow jet,150 main jet,and a DGJ needle on the 3rd clip.how do these sound.also if i switch to 40:1 from 20:1 which jets will i more than likely need to change?if you can possibly answer that.

 

i went from having no backpressure to having backpressure.is no backpressure bad for a two stroke.

 

anybody know??lol

 

i dono mutch but i think u need some back-pressure for something? lol

 

for a 4-stroke, a little backpressure is good for low-end torque.
For a 2-stroke, it's trickier, because while you want as little backpressure as possible, you need a contained flow to create something called 'cylinder scavaging'. That's why tuned pipes are so much better that a stocker, because they are just the right shape to use the expanding shockwave of exhaust gasses to actually pull the intake mixture IN to the cylinder, and help evacuate any exhaust from the combustion chamber. Since a two stroke doesn't have the benefit of a whole, separate stroke to push out exhaust gasses, this 'cylinder scavaging' is necessary for optimum performance. If you look at old pics of 2-stroke performance bikes, like drag-bikes, or race bikes, you will see they have this big cone sticking out the side by the exhaust port. When they were first figuring out how to tune a 2-stroke, they would use the cone like a tuned pipe, it was just FREAKING LOUD. Now they can model an efficient cylinder scavenging pipe that is also relatively quiet. So, I suppose that you could say that no back pressure for a 2-stroke IS good, but just running an open exhaust port won't work, even though it would be the least theoretical back pressure. Open headers on 4-stroke, yes, 2-stroke, no way!

Does that make any sense?

 

if you go here, http://www.hpt-sport.com/tunedpip.htm you can get a very technical explanation of what I was talking about.

 

yeh that made some sense.so if i made a straight silencer from the FMF Fatty back i wouldnt do any damage?im not going to use this to ride with.i just like the way it sounds when the powerband hits.ill just ride around our field sometimes with it.

 

I think that as long as you don't disturb the actual resonator portion (fat part) of the pipe, it's ok. But, don't quote me on that. Maybe the whole pipe is critical! Call FMF, they'll probably tell you.