decompression , manual and auto ?

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decompression , manual and auto ?

Post  xr honda to the max on Wed Apr 22, 2015 10:32 pm

l took a look at my spare engine l bought resently , it has low compression , haven't taken it apart yet , l took off the the valve covers off and see the manual set up opens the valve for less compression .So these bikes have auto decompression when crank over for start to aid in starting , how does this work ??.
l learnt from from second xr 650 r owner, which l purchased, that one needs to use the manual decompression hand lever , stating the purpose is too lub the engine with 10 cranks with the kick starter , lubs the crank and other areas as its a dry sub
After taken the valve covers off l see the right side exhaust is still open when turning over engine with kick starter is the valve need a valve adjustment
Also is their a description on a old topic on the decompression system so l under stand more
thanks mike
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Re: decompression , manual and auto ?

Post  xr honda to the max on Wed Apr 22, 2015 11:07 pm

l under stand the manual decompression lever
Wish to understand the auto system
The resent motor l purchased has a hot cam stage one l believe , will remove cam cover and head
May need directions , l have another engine which l may use the orginal cam
Any thoughts are welcome
thanks mike
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Re: decompression , manual and auto ?

Post  Mad Frosty on Thu Apr 23, 2015 8:07 pm

The stg1 and stg2 hotcams have no autodecompressor , you can still use the manual decompressor .
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Re: decompression , manual and auto ?

Post  Mad Frosty on Thu Apr 23, 2015 8:08 pm

Sounds like top end jobby from what i undrestand from you .
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Re: decompression , manual and auto ?

Post  xr honda to the max on Thu Apr 23, 2015 10:19 pm

l will take a look more closely and remove the cam cover top , l think l will install a honda cam with the auto decompression also
l see one exhaust valve could be adjusted it has no free play so valve maybe still open
Didn't know that stage one or two cams didn't have auto decompression set up
Any info on how the auto decompression works for starting purposes
thanks
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Re: decompression , manual and auto ?

Post  xr honda to the max on Thu Apr 23, 2015 10:49 pm

l still have a few xr500r drt bikes that l run .The decompression works on a cable , still do not know how the 650r works on kick starter set up
thanks
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Re: decompression , manual and auto ?

Post  BuRP on Fri Apr 24, 2015 10:12 am

The XRR's autodecomp works 2 ways.... no wait, the auto - part works only 1 way!

Auto: when the crank reverses direction an exhaust valve is forced open to bleed combustion pressure off so as to prevent the foot/ankle/leg/shin of the kicker from breaking, hence a safety measure.
Keep this in mind when adjusting the valves, only rotate forward.

The lever/cable assy allows you, hence manually, to bleed compression pressure off so as to position the piston closer to TDC than when this feature would not be there.
This we all do, by cycling the kicker until it gets 'hard', pull lever and push the kicker an inch or so further, then release lever and whack the bugger into life - and this is just a convenience thing. This way in fact we start the bike with a lesser compression than when it runs/idles, but because our legs are less powerful than the piston this makes life easier.

Only 2 cams have the auto decomp system on: the std cam and the (rare!) genuine HRC cam.
No other cam or hotcam has this on, also not any reground cams as the base circles are smaller and the system will not work anymore, it is taken off by those who regrind cams.
But, the manual lever/cable system will still work as it is a separate system altogether.
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Re: decompression , manual and auto ?

Post  xr honda to the max on Fri Apr 24, 2015 11:10 am

thanks BURP
think l got it now
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Re: decompression , manual and auto ?

Post  xr honda to the max on Sun Apr 26, 2015 2:34 pm

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Re: decompression , manual and auto ?

Post  xr honda to the max on Sun Apr 26, 2015 2:41 pm

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Re: decompression , manual and auto ?

Post  xr honda to the max on Sun Apr 26, 2015 2:42 pm

l was on you tube today and see n these videos , which related to my bike and will help out
thanks mike
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Re: decompression , manual and auto ?

Post  xr honda to the max on Sun Apr 26, 2015 2:59 pm

https://www.youtube.com/watch?v=wezL2KYt6CY
seen this as well , which will me understand bike more with the hot cam l have , but really think l will go with a original cam like the idea of the anti kick back decompression idea , saves on shins , l have three xr 500r and had some times back fire or kick back , HURTS much
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Re: decompression , manual and auto ?

Post  xr honda to the max on Sun Apr 26, 2015 3:01 pm

l see this is a L model but think simular in process
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Re: decompression , manual and auto ?

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