KR-1S.co.uk Forum

Anyone here owned one of these little beauties? Engine looks like a jewel, frame and running gear look ok too. What were they like good or bad any info appreciated

Supposedly the Tandem Twin was basically based on the Ar125's engine. Not owned one myself, but there's a full write-up in the Nov 2011 Practical Sportsbikes, a comparison test with an RD125LC.

Came in 2 versions, a 12bhp learner bike, and a 20bhp unrestricted version.

I remember them and also remember my best mate's brother having a red and white one. If I remember correctly, these were brilliant little bikes and I certainly have fond memories.

Post some pics up for us please.

I've had a soft spot for these li'l 2strokes for years. Rebuilt and tuned quite a few. Not many have been looked after and people never seemed to revere them as much as the AR50/80 or the RD and RG125.

I believe their time will come and prices will start to rise as they become rare. Currently I have five AR125's three of which are pretty good. They range from a 1983 A1B (first full power UK model) to a B7 (one if the last UK models made in 1990)

The frame, suspension and running gear is very good. The front forks and tyres are a little small by modern standards but perfectly capable.

The engine is very strong and is like half a KR250 with rotary disk valve and reed valves. It is very torquey and pulls very well, even in restricted 12bhp form.

The standard unrestricted UK bike has 21-22bhp and goes pretty well. On standard gearing 85-90mph is pretty easy. With a stage 2/3 tune the engine is capable of over 30bhp and with adjusted gearing exceeds 100mph. As you can imagine the more you tune, the more highly strung it becomes and ultimately fragile.

For me, the bike to get would be a model A1B, A2-A8 if you can find one as these are the unrestricted bikes. I believe these were quite common in Ireland. Not so common in the UK due to 80's learner laws.

Alternatively, the more common restricted bikes B2-B8 make a great starting point. They are not easy (read cheap) to totally derestrict to Kawasaki's original unrestricted spec (different head, barrel, carb, oil pump etc) but it is very easy to get the bike up to 18-19bhp with just a good expansion chamber, disk valve, ramair filter and careful rejet of the carb. Nothing too expensive or difficult.

Clearly I'm biased and a bit of an AR geek (says the missus). I think they are great fun. You can thrash em to an inch of their life and they keep coming back for more. Like all good Kawasaki 2strokes, just make sure you dont skimp on the oil quality.

See Diffrent Strokers Stafford show site and CMC charity ride out below for pics of my Green White AR smoker 

http://diffrentstrokers.com/stafford2011.htm

http://www.facebook.com/photo.php?fbid= ... 971&type=3


Cheers

Thanks for all the info there, that AR of yours you brought to Stafford was lovely.

I for one would like to see more pictures of your collection please.

Luders wrote:that AR of yours you brought to Stafford was lovely.

It certainly was, very nice to see one there. =D>

I'm lucky enough to have had a quick look at the other bikes too.

Engines on the way from Japan probably a bike in parts in the future. Will be used for Period 5 (pre 83) racing here so would appreciate links or scans of tests/articles on the bike as I believe they came out in 82????
The engine will go straight to stage XXXVI tune, with a 116mm rod and 56mm piston on the list. Has it really got the odd ball bore/stroke 55 X 51.99 or something?
Cheers

Iron barrel and disc valve induction.

The discs are rubber mounted and the splines shag out if you rev them too hard too often.

My younger brother had one. Quick for what it was.

I've checked the original japanese parts book I have for the AR125 A1 and it shows manufacturing commenced in 1982. I don't have any evidence of imports into the UK until 1983. Maybe someone can clarify the first date of import?

I have dates and listings for all models of AR including frame and engine numbers.

The barrels are Cast Iron and are not the easiest to port. The early model disk valves were all steel and were prone to wear on the splines. This was cured in the later models with the addition of a rubber damper in the centre of the disk. If your rebuilding an early model engine I would fit the later model disk valve as it works just fine.

The restricted disks can be cut to alter the timing, typically on the inlet from 95degrees to 120degrees before TDC with the exhaust 55degrees after TDC or you can fit the unrestricted disk. This is an easy mod giving immediate results more power and more midrange grunt.

Happy to discuss rebores / compression / port dimensions / timing for exhaust and transfers if anyone is looking to tune the engine. I'm not an expert by any means but I am willing to share what has worked for me.

Same with jetting of VM24 and VM26 Carbs to suit mods.

As for racing - I have contemplated taking a tuned AR to one of the Classic Track Days (see http://www.classicbiketrackdays.com/ ) as I know that it may not be the fastest but it would sure make me smile !

Cheers

55ATDC for closing is still way to mild, I'm sure the disc is the same as the KR, might have to make a little hub like a Rotax to hold a carbon fibre disc.

TwoStroke Institute wrote:55ATDC for closing is still way to mild, I'm sure the disc is the same as the KR, might have to make a little hub like a Rotax to hold a carbon fibre disc.

IIRC the AR125 is the same as the KR except for the actual timing. Mounting a CF disc valve on a custom hub sounds like quite a good idea.

Hi Guys,

Just scanned this from the current issue of Practical Sports Bikes.
(Only scanned the bit about the AR125)







Cheers,
Bernie

Thanks for scanning that Bernie, great article (I'm
Going to have to go and buy it now though )

I could pick fault with some of the details like they haven't mentioned the early AR A1/A1A/A1B models from 1982/1983 and the fact that the carb has no restriction (24mm B model/26mm A model), like all 2strokes change the tune and to get the best out of it you have to upgrade / or / and reject the carb etc etc.

Nevertheless I'm with them on the conclusions, the AR125 (to quote another AR lover) was never a bride in it's day, more the bridesmaid... However its time has come. It's a best kept secret - just how good they really are and I for one don't regret any I have bought.

With a garage that includes Suzuki, Hond and Kawasaki bikes I'm nearly always out on the AR because it's such a hoot !

(uh oh ok until I get the KR1R back on the road, LOL)

As for CF disk, this also sounds worth a try as long as it will fit in the casing space. It could be mounted/bonded on the newer disk rubbers maybe?

55 exhaust timing has worked for me with more gained by raising the exhaust and transfer ports and sorting compression. Always up for trying new ideas though...

Cheers

Thanks for the scans