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Discussion Starter · #3 · (Edited)
Thanks tmas
when raced back in the seventies the engine had extensive mods as my dad raced drag cars and was a engine builder
crank is lightened and stroked to 120cc it originally had a wiesco 54mm piston modified from another model
but since i rebuilt it ive used a takegawa R type piston that was to suit Z50 with takegawa roller head {124cc}
bore size 54mm and pin size 13mm and piston pin to deck hieght the same as the xr piston
this also gave me the right valve pocket relief and clearences to run the takegawa R type head its got now with sr35 roller cam
this takegawa head was to suit a xr100 took a bit of modifying to fit the xr barrel for correct alignment
the original head was ported with 1mm oversize inlet valve and running a PK roller cam cage with a modified web cam to fit the roller cage
if i remember the web cam was a 58c/58b with big lift over 330 thou at 0.050
barnet cevlar clutches,oil cooler,24mm pop yosimura tm flat side and takegawa manifold
originally had 24mm klien with straight shot PK finned manifold
PVL ignition system
exhaust fmf reverse mega phone
the front forks had spacers fitted to stiffen them up and goji air caps fitted
the rear mono shock swing arm is new as the original was a modified stock one my dad fabricated
and it was a bit rough and had some cracks in it
the original shock was a koni with different spring its now got a chinese one
engine runs on methonol and castrol R30 oil
have had it running sounds great and is fast to ride brings back memories
in Australia there is vintage moto racing and they still run a XR class might put it back on the start line again
got a couple of other projects nearly finished
cheers
Bruce
 

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Discussion Starter · #6 · (Edited)
Text Handwriting Font Diagram Document
Auto part Engine Automotive engine part Machine Carburetor
Hi Guys
found the flow spec sheet i used when playing around with the standard xr heads and the Takegawa head
the writing in the red is the flow rate for a std xr head {pretty piss poor}
the rest is after i played with the ports on the Takegawa head, first i flowed it straight from the box
then played around with the ports until got final figures listed
valve lift opening in thousands of inch on the far left
Also found picture of bottom end of engine showing stroker rod and old pvl button ignition
Cheers






 

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Discussion Starter · #8 ·
SL Mono Shocker

I love you're bike. Here is a picture of my SL mono shocker. Now it has a Daytona Anima 190. That XR is Trick!!!!
Very kool SL
Sl 70s pretty rare in AUS there is a couple with modified engines that race in the xr class
how much hp/kw does the Daytona motor put out?
posted a couple of pics of my old unrestored race dax in show us you dax thread
its on my list for a resto and engine rebuild
cheers
 

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Thanks. I haven't had it running since it was a 150 anima. But it ran really strong. Here is the 150 with a 70 mm crf150r piston and now also a ported head. I think it will make a easy 20 hp. It's a short stroke big bore 190. I always wanted to build a early XR 75 with a turtle lay down shock kit. They are so cool. I wanted to keep the big tank like you have but my inverted forks hit the tank so I had to use a later tank. I also have 14-17 wheels with disc brakes. My favorite year XR is a 1977. My friend had one when I was a kid
 

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Discussion Starter · #10 · (Edited)
Land vehicle Vehicle Motorcycle Car Motocross
Land vehicle Vehicle Motorcycle Automotive tire Motor vehicle
Hey Geezer
1977 honda barn find about a year ago
got a sprare tank for it and a recovered seat
cost 100.00 couldnt say no
bike had no ignition on it or carby when i got it so fitted up a chinese inner rotor kit and xr100 carby and manifold I had, and she runs
a bit smokey but i will rebuild the engine
will be a future resto
when i start it i will post all progress on this one
noticed it also has a Early rm80 suzuki front end and rear wheel with alloy rims
cheers
keep me posted on your SL 70 engine build looks like your putting alot of effort into it
should be a handful on the track
View attachment 155541 View attachment 155542
 

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Discussion Starter · #12 ·
ajcmbrown,the ignition system is a cheap honda 50 one off ebay
the trick is modifying it to fit the xr
things to modify listed below

altering the taper on the rotor in a lathe
shortening the posts on the stator to align rotor magnets to stator pick up
modifying the mounting plate and redrilling the holes and indexing the holes so the plate run true to the rotor
then as you cant use a keyway on the rotor as it is set wrong
because the 50 engine is horizontal type and the xr is vertical type
that means key way location is wrong for TDC
so setting up the timing approximately to tdc, get it running and dial it in with a timing light
thats why you don't see them fitted much
you can get one off a bloke in Melbourne set up already
Andy from big 50s race and retro he has been dabbling in mini bikes and pit bikes and sells a lot hard to get bits
including a cdi ignition for xrs around 250.00
or if you want to spend some bucks xr mini racer in the usa ,Alex judd can get you a tailored PVL unit the will bolt straight up for around 500.00 delivered to OZ
thats what im running one the old KO XR75 in the engine pics above
 

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Thanks for the reply sgtbilco, I purchased a crf50 chinese ignition system and coil, and your instructions are spot on other than the taper, it seems to fit quite well on my '77, I have yet to fit it but I have arrived at the very same conclusions as you describe above, with the exception of the shortening of the posts as I haven't got that far yet, I may get to it one night this week.
All up cost, $80AUD so if it works like a suspect it will, a very cheap conversion.
I will post pics of the mods required as I go.
 
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