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Author Topic: Exhaust and jetting  (Read 478 times)

jedaks

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Exhaust and jetting
« on: February 10, 2014, 04:57:13 PM »
Curiosity question.

Why is it that a free flowing exhast leans out the fuel mix? How does that work, considering the engine has already turned the fuel into energy and it is expelled beyond the exhaust valve?

Conversely, why does a more restrictive exhaust richen the fuel mix?

Thanks

ace.cafe

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Re: Exhaust and jetting
« Reply #1 on: February 10, 2014, 07:20:03 PM »
Because the scavenging of the cylinder changes, so there is less burned and unburned gasses left in the cylinder. These exhaust gasses have the effect of making the engine burn richer.When the exhaust gets more completely scavenged, the mixture is more pure than it was previously, so re-jetting is needed to meet the new combustion conditions which have more fresh air in there..

A less restrictive exhaust system gets more of the exhaust out of the cylinder. A more restrictive exhaust system leaves more of the exhaust inside the cylinder.
« Last Edit: February 10, 2014, 07:24:06 PM by ace.cafe »

Hoosier Bullet

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Re: Exhaust and jetting
« Reply #2 on: February 13, 2014, 12:05:57 AM »
for the high-falutin':
le chatelier's principle
google it.

Sorry Tom, couldn't resist chiming in even though you already explained it.  The workings of the whole damned universe operate on this one!

ace.cafe

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Re: Exhaust and jetting
« Reply #3 on: February 13, 2014, 01:07:32 AM »
for the high-falutin':
le chatelier's principle
google it.

Sorry Tom, couldn't resist chiming in even though you already explained it.  The workings of the whole damned universe operate on this one!

Thanks Justin!

I'm gonna use that one from now on!

X-file

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Re: Exhaust and jetting
« Reply #4 on: October 25, 2014, 02:03:45 PM »
The people at Amal don't claim that a less restrictive exhaust requires a bigger main jet.
They advise that if you remove a muffler and run a straight pipe, it's likely you'll need one size smaller main jet and one size larger slide cutaway (leaner).

Only if you fit an open mega do they recommend a main jet increase (about 3 sizes).

It's always worth doing a main jet test, in any case.

ace.cafe

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Re: Exhaust and jetting
« Reply #5 on: October 25, 2014, 02:11:32 PM »
L.O.L. !!!
« Last Edit: October 25, 2014, 02:13:40 PM by ace.cafe »