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The effect of exhaust on compression

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thekeeper199
Borekit Bruiser



Joined: 08 Feb 2014
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PostPosted: 20:12 - 11 Jul 2014    Post subject: The effect of exhaust on compression Reply with quote
Hi, holes in the exhaust muffler effect the engine compression?
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mjn51
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Joined: 04 Feb 2011
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PostPosted: 20:18 - 11 Jul 2014    Post subject: Reply with quote
No ,but holes in the piston do
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Nobby the Bastard
Harley Gaydar



Joined: 16 Aug 2013
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PostPosted: 20:18 - 11 Jul 2014    Post subject: Re: The effect of exhaust on compression Reply with quote
thekeeper199 wrote:
Hi, holes in the exhaust muffler effect the engine compression?


No.

BTW it's affect, not effect.
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thekeeper199
Borekit Bruiser



Joined: 08 Feb 2014
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PostPosted: 20:46 - 11 Jul 2014    Post subject: Reply with quote
Klx250 previous owner had drilled holes in the muffler for noise
Btw how can i know the good compression test result for that specific bike? I mean what is a bad compression.
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RhynoCZ
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Joined: 09 Mar 2012
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PostPosted: 20:53 - 11 Jul 2014    Post subject: Reply with quote
thekeeper199 wrote:
Klx250 previous owner had drilled holes in the muffler for noise
Btw how can i know the good compression test result for that specific bike? I mean what is a bad compression.


Bad compression is no compression. Thumbs Up

Find the manual and read it.
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Dalemac
World Chat Champion



Joined: 15 Oct 2006
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PostPosted: 22:02 - 11 Jul 2014    Post subject: Reply with quote
I think you are getting confused with compression and back pressure.

https://en.wikipedia.org/wiki/Back_pressure
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Sload
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Joined: 28 Aug 2011
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PostPosted: 22:07 - 11 Jul 2014    Post subject: Reply with quote
https://www.veryuseful.com/mustang/tech/engine/exhaustScavenging.pdf
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Ariel Badger
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Joined: 02 Dec 2006
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PostPosted: 23:13 - 11 Jul 2014    Post subject: Reply with quote
Exhaust can affect performance but it does not alter compression ratio
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thekeeper199
Borekit Bruiser



Joined: 08 Feb 2014
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PostPosted: 23:33 - 11 Jul 2014    Post subject: Reply with quote
thanks for the replies.. i understand.
my model have the auto compression release..
means the compression ratio should be lower?
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Dalemac
World Chat Champion



Joined: 15 Oct 2006
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PostPosted: 23:36 - 11 Jul 2014    Post subject: Reply with quote
thekeeper199 wrote:
thanks for the replies.. i understand.
my model have the auto compression release..
means the compression ratio should be lower?


OK, what is making you think you have issues with compression?

The only thing you have mentioned is some holes in the exhaust. This will affect only exhaust back pressure and not compression.
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thekeeper199
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PostPosted: 23:44 - 11 Jul 2014    Post subject: Reply with quote
cause according to the mechanic i have 70PSI and he did mention "auto compression release"
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Dalemac
World Chat Champion



Joined: 15 Oct 2006
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PostPosted: 23:55 - 11 Jul 2014    Post subject: Reply with quote
thekeeper199 wrote:
cause according to the mechanic i have 70PSI and he did mention "auto compression release"


Right. That is meaningless unless you know what RPM the test was ran at.

Auto compression release just reduces the amount off compression until the pistons are moving quick enough to start. The valve then closes, the spark plugs kick in, and your engine starts.


If the bike starts easily and runs well, your compression is good enough.

If not, you will want to think about replacing the piston rings and at least checking the valves are sealing properly.

It has absolutely nothing to do with the holes in your exhaust.
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thekeeper199
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PostPosted: 00:47 - 12 Jul 2014    Post subject: Reply with quote
okay. thanks for the explanation. basically on cold weather bike starts then stalls 1 - 2 times then runs fine. on normal days it starts fine.. does this consider as bad start?
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thekeeper199
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PostPosted: 10:00 - 12 Jul 2014    Post subject: Reply with quote
this is the EFI model so choke is auto...
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Old Thread Alert!

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