Another CR500 question for Eric Gorr

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#1
In another post you mention that you bore the cylinder 1mm over to eliminate
the decompression ports. What is the reason?
Thank you
 

EricGorr

Super Power AssClown
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#2
The decompression grooves make it easier to kickstart but they do sacrifice some BMEP and the way the expansion wave forms in the exhaust port. For the application of roadracing, maximum power (75-85hp @ 8,250 rpm) you can afford to inconvenience your kickstarting leg. Besides, most of these bikes are started with a electric motor and roller on the rear wheel.
:)
 

EricGorr

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#4
That depends on the skill level of the guy riding it and the available traction. In some cases I make the grovves deeper and open sooner just to take the hit out of the power. That works good for guys riding over rocks and roots. My thoughts are that if a guy wants to detune a CR500 that much then he should just buy a KDX instead.:silly:
 
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#5
Thank you very much..I had a CR250 cylinder ported by you a while back and I would like to get my CR500AF ported. I ride sand dunes and motocross therefore I need a very broad spread since some of the tracks I ride are very tight while the dunes are wide open. Would you recommend boring it out to the next oversize as well? Is it possible to make a 500 have more power and be smooth too?
 
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#6
BigCR,
I have a '91 CR500 that was ported for a broad smooth delivery and combined with a flywheel weight is surprisingly easy to ride. You will always have to show it a little respect, but it isn't as wild as stock. It seems to have less hit in the low to mid area and a lot more top end......much more than you would expect from a 500. I'm sure Eric could help you out.

Eric,
Do you know of people haveing any luck road racing a CR500 motored bike? I was going to do something like this but everyone I talked to said this was a bad move. They said that crank life was very short under the sustained high rpm use. Do you change anything in the bottom end or just live with an accelorated replacement schedule?