12th Oct 2017, 20:14
Blimey, major lack of AR knowledge.
I'm just writing this on the hoof, but I've got a garage full of AR stuff.
Running the KH400 piston after trimming the skirt and removing about 3mm from the barrel bottom (will need to check) and a head reprofile plus a fair bit of port work sorts the power plant out, even with the restricted cool. The coil seems to be a red herring. Portwork is not hard, but you need the tools to work the transfers properly.
You need to extend the disc valve closing by a good amount and the opening by about 2mm.
Reprofile the disc cover and open the reed stops by 2mm and flow the inlet tract. Forget the 26mm carb, use a KR1s Keihin PWK 28mm flat-slide as you get a better throttle response and it's bigger oh and hassle Padgetts - they made a pipe called 'top speed' that was a chrome chamber and stinger with an alloy can. Nice.
You will need to gear up by (at least) 1 tooth as it will rev clean out in top after all this and you will probably kill it, so go premix and a good fuel - 4 star prefs.
The air box is optional, but unless you're racing I'd keep it. Strokers like airboxes from a health and reliability point of view.
The problem with handling is the the top yoke and chassis - it flexes like a jelly d*ldo and will lowside you, so plate it up... don't be shy, good thick steel is needed and get a steering damper / fork brace and slightly heavier oil. Go 1 bigger on the rear boot and leave the front stock.
You don't have to throw a fortune at it, just find the right people.
Peterborough Kawasaki and Padgetts were great as was Uncle Bob... Bob Farnham of course, the god damn genius!
You can easily see 25hp as an AR145; the extra 20cc'c make the PWK28 work well and it retains a good induction pop when the disc valve opens.
You can make reasonable gains from a stock engine / pipe and carbs, but it struggles to shine. Get an RDZ or a TZR instead if you want easy power.