Tuning the KR

I have left the old words in yellow as some of it is still relevant - have learnt quite a bit over the years so to distinguish between the old and new the more recent stuff is in Kwack green. (18 Oct 2003)

First the disclaimer. I mess about with engines for fun and I do not claim to be a tuner. If you do not know what you are doing and are not willing to get it wrong then I strongly recommend that you get a professional tuner to work on your engine - it will probably be cheaper in the long run. If you mess up a set of barrels it will cost ~£500 for a new set (good second hand barrels are very rare). To minimise errors I have a set of scrap barrels that I practice all the modifications on, before applying them to my good barrels. As the modifications are aimed at increasing flow, the way I test if the flow has increased is to hold the barrel under a tap and pour water into a standard port. I increase the flow until the port can't flow any more water. Leaving the tap on that setting I then pour the water into the modified port. If it can flow more you can open up the tap. You can also see how the flow from the port is angled into the barrel, and how turbulent the flow is. Getting this right is important. Opening ports up without taking account of the flow into the barrel can mess things up. I don't have a proper porting tool (~£300 and £500) so I have to make do with a Dremel. I recommend great care if you use one of these as it is very easy to slip and score the barrel (replating the barrels will cost between £200 and £300 pounds). Use as small a cutter as possible and take your time. I tend to use an engraving tool as this only cuts very small amounts, you can run it at very high speed and if you slip the damage is minimal. Though I like playing with the engine, I just don't have the tools or the experience to build an engine as well as a professional. Having tried a KR-1S which had been put together by Graham File, I was so impressed with the way the engine drove (I don't think the bike was quicker than mine but it was easier to ride) I have got Graham to rebuild my engine this winter (99). What follows is a list of the modifications I made that appeared to work. The result of my efforts was one of the quickest if not the quickest KR-1S in the races I competed in. If you want to know what Graham can do for you then give him a call on 01303-262222. All the above is still relevant the only thing I have done is buy myself a small tool (FOREDOM) that allows me to get into a port. It isn't ideal as it is too small (not enougth reach on the piece) and bits are limited.

Harmen Lambrects has been running a home prepped KR in Holland and has kindly passed on info about the preparation of his bike. There are plenty of good tips on what to do and not to do. As with anything I have said if you mess with your engine than the risk is yours. If you unsure what you are doing get a proper tuner to do the work.

According to the workshop manual a stock KR1 should make about 55 hp and a KR-1S about 60 hp this probably converts to about 50 and 55 hp at the back wheel. To be competitive you need to be making over 60 hp hopefully closer to 65 hp. To get this without messing up what is a pretty good engine is not easy. The KR runs the same bore and stroke as the RGV and Aprillia (which is an RGV) and the early 90's TZ250. The TZ's put out between 75 and 80 hp. You won't be able to match that but you can pinch ideas and bits from the TZ's. Also it is worth having a look at what they get up to tuning RGV's and Aprillia's. These engines being a little newer have quite different porting, ignition systems and power valves to the KR. For what it is worth - it looks like all the manufacturers have abandoned the 56x50.6 format used in these engines and have gone over to the 54x54.5 used by Honda, the new RGV and TZ's using this bore and stroke.

If you have not already done so, have a look at the tuning bit on Dave McGeachie's KR-1S website http://www.kr-1s.net/

We spent a day at the dyno trying a number of bits reults are off this link

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Material Copyright © 2000 Mark Jordan