Sputtering on deceleration... normal?
11-09-2009, 02:13 PM
#1
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Superstock
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Join Date: Sep 2009
Location: Woodland Hills, CA
Posts: 421
Sputtering on deceleration... normal?
Hi all,
So I've had my SH about a month and a half now... and after sorting out a few issues. I love it!
The only issue I seem to have now, and it may actually be a non-issue, is the way the bike sputters when it decelerates. How much should the bike do this, and should I even be concerned?
- Mike
So I've had my SH about a month and a half now... and after sorting out a few issues. I love it!
The only issue I seem to have now, and it may actually be a non-issue, is the way the bike sputters when it decelerates. How much should the bike do this, and should I even be concerned?
- Mike
11-09-2009, 02:21 PM
#4
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Superstock
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Join Date: Sep 2009
Location: Woodland Hills, CA
Posts: 421
No backfiring... just an irregular gurgling. it gets stronger with engine braking.
The bike is completely stock and still has the PAIR system in place.
I figured it was just part of the v-twin sound... my buddies Ducati 900ss makes some similar noise. Just thought I would ask to be sure.
The bike is completely stock and still has the PAIR system in place.
I figured it was just part of the v-twin sound... my buddies Ducati 900ss makes some similar noise. Just thought I would ask to be sure.
11-12-2009, 09:29 PM
#9
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Join Date: Oct 2009
Location: Newport, RI
Posts: 143
PAIR Valve purpose
This is actually precisely the purpose of the PAIR system. PAIR stands for "Pulse secondary AIR injector". I believe the PAIR-ectomy thread explains this. In short, those sounds are pulses of air micro-exploding in your exhaust
system in order to burn off unused fuel that gets sucked through the engine on deceleration, especially engine braking. The fuel is there because the vacuum is disproportionately strong in relation to the throttle position, and as a result, the carbs provide more fuel/air mixture than is optimal for the situation, so not all of it gets combusted in the cylinders.
I think I got that right...
This is one of the many reasons nobody uses carburetors any more. As elegant as some of them are, they are a total hack compared to modern fuel injection. Carbs are all about coercing the laws of physics into doing something pretty close to what we wish would happen as often as we can get away with. FI is all about deterministically making exactly what you want to happen directly happen at all times.
I would be *very* interested in riding a FI'd hawk (ok storm) someday.
system in order to burn off unused fuel that gets sucked through the engine on deceleration, especially engine braking. The fuel is there because the vacuum is disproportionately strong in relation to the throttle position, and as a result, the carbs provide more fuel/air mixture than is optimal for the situation, so not all of it gets combusted in the cylinders.
I think I got that right...
This is one of the many reasons nobody uses carburetors any more. As elegant as some of them are, they are a total hack compared to modern fuel injection. Carbs are all about coercing the laws of physics into doing something pretty close to what we wish would happen as often as we can get away with. FI is all about deterministically making exactly what you want to happen directly happen at all times.
I would be *very* interested in riding a FI'd hawk (ok storm) someday.
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