Ok, there is definitely going to be a lot discussed here (depending on who replies). I've had many bikes over the years and I'm beginning to challenge the assumptions I've had about rejetting a carb due to changing the exhaust. Let's get after it.
It has always been known to me that a change in exhaust will need a change in jets. That was usually because of decel popping, backfires, and/or the result of a lean or fat condition after the change.
I completely agree with what Sense said in another post. To paraphrase, the flow of an exhaust cannot change what the intake pulls in from the air box. Which makes perfect sense to me.
And if that is the case, then why does a bike's air/fuel mixture appear to lean out or enrich after the exhaust change? There is some valve overlap (at least, I think I'm right about this) when the compression stroke near the top pushes gasses out just before the intake strike pulls in air/fuel. Is it possible a free-er flowing exhaust created a low pressure area in the exhaust that during the valve overlap caused some of the incoming air/fuel to leave the combustion chamber before the exhaust valves fully seated?
Or maybe the rejetting is "necessary" because the exhaust muffler hid the (what I am now learning) normally occurring decel pops, but now a richer mixture is needed to prevent it altogether.
If that is the case, and a richer mixture is needed (desired more than needed), then why do I hear decel popping is a rich condition where unburned fuel is reaching hot air in the exhaust and igniting? A richer mixture would make that worse instead of fix that, right?
Or maybe, just maybe, the 'need' to rejet is not a mixture problem at all. Is it truly a naturally occurring thing that doesn't need attention, and if you do address it the solution depends on THAT bike's configuration and how it is running? Which makes more sense to me than what I previously thought was correct.
Let the replies come!
It has always been known to me that a change in exhaust will need a change in jets. That was usually because of decel popping, backfires, and/or the result of a lean or fat condition after the change.
I completely agree with what Sense said in another post. To paraphrase, the flow of an exhaust cannot change what the intake pulls in from the air box. Which makes perfect sense to me.
And if that is the case, then why does a bike's air/fuel mixture appear to lean out or enrich after the exhaust change? There is some valve overlap (at least, I think I'm right about this) when the compression stroke near the top pushes gasses out just before the intake strike pulls in air/fuel. Is it possible a free-er flowing exhaust created a low pressure area in the exhaust that during the valve overlap caused some of the incoming air/fuel to leave the combustion chamber before the exhaust valves fully seated?
Or maybe the rejetting is "necessary" because the exhaust muffler hid the (what I am now learning) normally occurring decel pops, but now a richer mixture is needed to prevent it altogether.
If that is the case, and a richer mixture is needed (desired more than needed), then why do I hear decel popping is a rich condition where unburned fuel is reaching hot air in the exhaust and igniting? A richer mixture would make that worse instead of fix that, right?
Or maybe, just maybe, the 'need' to rejet is not a mixture problem at all. Is it truly a naturally occurring thing that doesn't need attention, and if you do address it the solution depends on THAT bike's configuration and how it is running? Which makes more sense to me than what I previously thought was correct.
Let the replies come!
