KR1-S Airbox

Engine Tuning Pt I A(let it breath)

In this bit I hope to show how to fit a bigger set of carbs. So far I have some carbs, airbox plus rubbers and inlet rubbers

Standard and bigger carbs

If you manage to get a set of PWK 35 carbs these are the jets and needles you should have - source Autodata 2000 (ISBN: 0-85666-922-9)
There is a difference between the carbs on the various models of KR Table below shows what I have managed to glean so far. Still got to add slide sizes as they have different cut aways.

Bike	KR-1R	KR1	KR-1S C2	KR-1S C3
Carb	PWK 35	PWK 28	PWK 28	PWK 28
Main Jet	145	135	135	135
Idle Jet	40	38	40	40
Needle Type	R1327J	68A	68X	99E
Slide

First up Keihin have changed the nomencluture they use for their needles a R1327J is now a CEN. Secondly we have found that the main jet and needle are to weak. For our engine with semi pressurised air box we have found that a jet around 155 is correct 20 ° C 1000mB 50% humidity. For a needle we have gone to a DEN slightly richer on the taper. Clip 2nd from bottom.
PWK Carbs are listed here http://www.pro-flo.com/proflo_keihin_flat_slide_carbs.htm#PWK%20SERIES for about £75 + import duty

A couple of links to American sites listing Keihin Carbs. The first also has useful info on setting the carbs up. http://www.carbparts.com/ and http://www.ctracing.com/carbs%20&%20reeds.htm

Though I have the rubbers and carbs I didn't have the reed block inserts so have had to mod a set of standard ones. The green ring is the amount a standard block needs to be opened up. As this makes them a bit thin I filled them with body filler before starting - good job to as I have broken through to filler in a couple of places.

Reed block insert modded for 35mm carbs

Hit a problem. When re-assembling the reed blocks noticed that the reeds were damaged. It is the corner of three of the four reeds have broken off. In the piccy, sorry it is difficult to see, the corner of the reed has gone and the black bit is a gap between the reed and the frame. Looks like a set of reeds before the dyno test.

broken reed

Finally fitted the carbs - I have used the standard choke cables as they seem to fit - the tails could do with being a bit longer. I will check this a litlle more carefully when I split the engine. Piccy only shows one but both are in along with the airbox. It is all very tight but everything fitted beautifully. I was paranoid about fitting the trumpets as I didn't want to damage them as they are no longer available. After a bit of a struggle they just slipped on. Changing mainjets will still require removing the airbox and carbs. But at least you don't have to struggle with the float bowl. There is a little inspection plug in the bowl that allows jets to be changed. I will try the carbs without the pressurised box first then will plug all the breathers into the airbox to get the ram air working.

35mm carbs going in - it's tight but they fit

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