RGV250 Sp VJ23.

Sorry about the state of this page, other things have taken priority,



ChartObject 29K-50 YPVS

With the pot set fully clockwise the timing will be static as per graph. Just off fully clock the timing will be "BDK RANGE". The timing is adjustable in between "BDK RANGE" and "DEGREES 29k-50,31Y/K-50,52Y-50 & 1UA-50" With the pot fully anticlockwise the timing will be standard to your particular cdi (degrees 29K-50,31Y/K-50,52Y-50 & 1UA-50) Note: the initial start point (degrees btdc) can be changed by advancing/retarding the stator plate. This will advance/retard the whole curve by the amount it is moved.
Cost of modifying a YPVS CDI is 140.00 + vat.

This is an example of fitting one of our CDi's to a Stan Stephens tuned 350YPVS, FII Race Bike, the Power Valves are fixed in the fully open position, it has Bored Standard Carbs with Ledair nozzels, Jolly Moto Pipes, with an airbox. 350MJ and C5 on the needle. Dyno1 Dyno2 The Standard CDi was 1UA-50.

We ran with the advance set at mid position, 12 O'Clock, and got more or less the gains shown, we jetted to suit, and then reduced the advance untill we started to loose power, this was about 11 O'Clock on the adjusting pot.

Dyno1 Dyno2

We have always tuned and prepared the LC's, YPVS350's and TZR's for racing, and as this has become more popular, we are now preparing more machines for racing. Obviously our main work is the engine, this is where our passion is, however with more and more rules, one has to stay ahead. Weight for these old machines has never been their strong point, so we have started producing light weight components, for example: suspension tie rods, and race wiring harnesses, hollow wheel and swingarm spindles. As I am sure you can appreciate, weight gains performance everywhere, cornering, braking and accelerating. Whereas HP only gives you better acceleration. Pictures below. The standard ones are 0.5Kg each, the new ones are 155g each.

The Tie Rods are £85+vat a set. This includes 2 Hard Aluminum shims per linkage.

Std Ones.

The shorter ones are favorite because they lift the back of the bike about ¾”. Not really enough to visually notice, but exactly what they need, probably closer to what they would have been when they were new with new shock and tall old section tyre.

Cart Shorter Ones.

Tie Rod Tie Rods Tie Rod

RD/RDZ 500
Power Valve Bhp/ Rpm

Power Valve Control




With the adjusting pot fully anti-clockwise the timing will be standard(47x or 1ge). Fully clockwise is the same timing asTZ500 (corrected for con rod,stroke length). The std ignition cuts out approximately 5% of the sparks at about 9800rpm increasing to approx 20% at 12000rpm. This circuit is completely removed and will not effect the timing even in standard setting.
We are currently charging 140.00 for the ignition(CDI) modifications and 140.00 for the p/ valve control units, however, if they are ordered/done as a pair we are charging 240.00 in total. The reason for this is that they do complement each other and it is easier for us to set up.


As can been seen from the graph, the optimum point to close the p/valves (on this bike), would be approx. 7100rpm,where approx. 8bhp would be realised from 7100 to 8300 rpm. This very much depends on how mismatched the p/valves are to start with. The example shown had been optimised for mid range power, with loosing too much top end, before adjusting the p/valves. However, although Suzuki say the valves turn at 7800 this varies by at least +/-200rpm. There is a time delay from p/valves starting to close to actual closing point, we have tried to address this by adding a circuit to sense rate of change of rpm . A high rate of change will start to open the valves approx. 180 rpm earlier,(1st or 2nd gear) and a low rate of change (6th gear) will start to open the p/v's 180 rpm later than set. In the example p/v's started to turn at approx. 8200rpm. The best way to find the optimum point is by running on a dyno with valves fixed closed, and then open, to get the curves as above. The range of adjustment is from 6000to 8000 rpm with a calibrated and graduated scale. There is also a calibration pot (which should not require adjustment) that could be used to extend the range. Cost of modifying your SAEC control unit 160.00 Supply modified unit 260.00.

saec control unit



The Graph below shows the effect of changing the power valve timing on a Graham File Tuned TZR250.
This is the only change that was made, no jetting, ignition timing or adjustments of any kind.

TZR250p.valve Re-timed

Power Valve Control
Below are some of the options for changing the power valve starting to opening rpm and the fully open rpm's.
Above example was using the standard TZR250 1KT program. This was reprogramed to prog' 14 (Top Row). As you can see this changed the initial movement of the power valve from 5850 rpm to 6000rpm, and the power valve was not fully opening untill 10050rpm this was changed to 8550rpm, the power gains are seen above. The eg' for the RD/RDZ500 uses RD500 (standard) and is reprogramed to prog' 8, for mildly tuned engines or prog' 18 for highly tuned engines.
The switch options 1 to 12 are fitted so all the programs listed are available by turning different combinations on/off.

Clear as mud?
The cost of modifying a P,Valve control unit to do all these things is 140.00 + vat.

 YPVS adjustable P.Valve Control


Contact: mail James  

Telephone: 01508 481713 Fax: 01508 481714 Ashwellthorpe Industrial Estate, Norwich, NR16 1ER