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Author Topic: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp  (Read 45759 times)

Offline teazer

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #390 on: Sep 02, 2019, 10:17:26 »
It's hard to tell from the pictures but I hope that it's the exhaust port that's polished to prevent (slow down at least) carbon build up and the intake is rough to prevent fuel puddling, and not the other way round. 

Your buddy does nice work in the ports BTW.

Now the seats need to be cut and blended in.

Offline JadusMotorcycleParts

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #391 on: Sep 03, 2019, 07:15:46 »
It's hard to tell from the pictures but I hope that it's the exhaust port that's polished to prevent (slow down at least) carbon build up and the intake is rough to prevent fuel puddling, and not the other way round. 

Your buddy does nice work in the ports BTW.

Now the seats need to be cut and blended in.

Pretty sure he has done things right.  He will do the final valve seat cuts when the valves are finished :)

Offline JadusMotorcycleParts

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #392 on: Sep 03, 2019, 07:51:19 »
The slow rebuild continues.  You can see that the clutch side of the crankcases is much emptier now without the electric start drive and its centrifugal engagement assembly (much lighter too ;) ).  Also got the cover plug out and installed the kick start seal.  Just waiting for the final head work  ;D

Offline Sav0r

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #393 on: Sep 03, 2019, 09:47:59 »
You should lop off the majority of the starter boss. Might only save a few grams, but it works with your build. I reckon it wouldn't be much of a project to do.
Sav0r the adventure.

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Offline irk miller

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #394 on: Sep 03, 2019, 11:49:46 »
Has anyone done a gram for gram comparison between the electric starter bits and the kick start bits?  The kickstarter mechanism on my XS650 engine, which includes the arm itself, the shaft and all gears, is heavy as hell. Not saying the kick start deal is heavier, but if we're talking about just a few grams, while keeping the ability to just push a button to start, many would choose the electric option.  Seems like everyone's first inclination, when it gets in their head to lighten the bike, is remove the electric starter.

Offline Sav0r

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #395 on: Sep 03, 2019, 13:54:01 »
Probably because in many cases you can get rid of all or most of the battery too.
« Last Edit: Sep 03, 2019, 13:58:39 by Sav0r »
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Offline Sav0r

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #396 on: Sep 03, 2019, 13:58:24 »
The kickstarter spline shaft (for lack of a better name) could be partially center drilled. Just go deep enough that you don't penetrate through the back side. A fabricated tubular aluminum kickstarter lever would be nice too. Lot's of weight to be shed there.
Sav0r the adventure.

Visit www.chrislivengood.net to get more information on my RD350 dubbed Mia Wallace as well as my other projects and snafus.

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Offline crazypj

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #397 on: Sep 03, 2019, 21:19:31 »
Kick-start lever is probably a 'standard ' Yamaha spline so one of the motocross bikes may have a direct bolt on ally kick-start lever? As for electric start, as pointed out, even on XS 650 you save at least 10 lbs by removing it and all the reduction gears then use a much smaller battery. BTW, are the valve springs one off or are they a standard fitment on something?
« Last Edit: Sep 03, 2019, 21:21:07 by crazypj »
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Offline hooligan998

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #398 on: Sep 04, 2019, 00:29:37 »
Get rid of kick start and the electric starter motor.  Just push start it everywhere.  It should be light enough. :P

Offline teazer

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #399 on: Sep 04, 2019, 00:42:29 »
You can drill right through the shaft to at least 50% of the shaft diameter to lighten it and then insert a short aluminum plug in each end.