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Old 08-01-2013, 01:33 PM   #16
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Joined: Jan 2011
Location: Summer: Kemiö, Finland; Winter: North Germany
Oddometer: 872
May be old fashioned, but this are some of the tweaks KTM made to tweak their MX models to Enduro bikes in the end of the eighties:

- they restricted the air flow through the airbox, A
- a thicker head gasket, B
- a heavier flywheel, C
- a more restricted rear silencer, D
- a smaller carb, to add something else, ( will increase low and mid throttle and decrease high end power output ).

A and C are certainly too done to get the moise output down.
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Old 08-02-2013, 07:36 PM   #17
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Joined: Aug 2013
Location: Texas
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Maybe a pipe and expansion chamber that favors the low end? Provided you could find someone who makes one for that model.
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Old 08-03-2013, 05:22 AM   #18
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You can strangle output with pipe/carb/timing but it's the port timing that sets the stage for RPM efficiency range. Cutting the cylinder base .030"/.75MM and adjusting squish to suit will be the most efficient way to tame output. Some tuning from there will adjust to suit preferences. It will still be a compromise with the pipe/carb.

Me? I'd give Scott Clough a call.
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Old 08-03-2013, 02:39 PM   #19
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Location: Oregon City Orygun
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Also RB designs in Portland can/may help you too, nice guy and some what local to you
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Old 08-03-2013, 02:45 PM   #20
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Location: chico,just below rag dump(nor-cal)
Oddometer: 12,901
The CDI box makes a huge difference in how the thing runs,the box off the enduro model might make a huge difference.

But any modern 2 stroke should have decent low end already rt out of the box,its the old clunkers that are peaky screamers.

Make sure the top end is fresh and see what sort of flywheel can be fit.
Also check that the power valve isnt stuck.

Or buy a bone stock KTM 300 most any year,they run great!
Some bikes around at times
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Old 08-03-2013, 03:00 PM   #21
Joined: Jan 2011
Location: You're Mama
Oddometer: 3,773
The power-valve is a good idea too. Keeping it closed / down , lowers the exhaust port.
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Old 08-05-2013, 10:19 AM   #22
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Joined: Feb 2006
Location: Corvallis, or-a-gon
Oddometer: 67

Thanks for the responses. Just got off the phone with Eric Gorr and intend to send him my top end for porting.

The 300E is the enduro bike. However, I believe this vintage shares porting with the MX bikes. It came with an alternator, which added some flywheel weight. To add more you need to remove the alternator rotor, so it ends up being a wash.

I have had the power valve governor shimmed shut. It helps, but the transition into the power band is still pretty brutal. I haven't measured the porting but I suspect from the behavior that the exhaust timing is too long as is the transfer timing.

For the price of a porting package, plus what I paid for the bike, plus my distate for riding orange, seeing what Eric can do with the welder, mill and some epoxy is worth it.

Plus 1 week turn-around.

I'll report on the completed package.

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Old 08-24-2013, 06:10 PM   #23
Joined: Apr 2007
Location: Ohio
Oddometer: 15
You can make your exhaust flange longer (maybe an inch) will move the powerband up to a higher RPM and but hit a harder.

On one of my bikes my longer tuned put me on the pipe at 6500 rpm's instead of 6000.
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