RULES

If you have any technical questions regarding the Supermono class, please email our Technical Representative (see below). Past questions are listed below.

Technical Questions

If you have any technical questions regarding the Supermono class, please email our Technical Representative by clicking HERE.  

Question 1

Hi, I have an SRX600 motor it is 10.5:1, 640cc, big valves, motor cross spec cam.  it also has a very free (read as bloody loud) exhaust. I have fitted it with 32mm keihn round slide carbs from the GPX 250.  My question is what size jets should I use? 

Regards, 

George

Answer 1

As a starting point I would use 130's, but for any engine the only way to be certain is to set the bike up on a dyno equipped with a lambda sensor which will tell you exactly what the air/fuel ratio is. Singles are not that fussy with the fuelling and you want to be running slightly rich to be one the safe side, so if you are not going to use a dyno then 140s would be your best bet for all round use (A/F ratio that you should be aiming for is approx 12.5 to 13).

If you do use a dyno then bear in mind that the jets that are appropriate for that day may well be inappropriate for other days - a hotter day will require a leaner jet and a colder day a richer one; although Kehien jets go in steps of 2 so there is a lot of scope for fine tuning; which is not really worth it on most singles - a step of 10 is generally OK. (essentially within reasonable limits, running too rich will make the throttle response a bit fluffy, but being too lean will cause you to melt pistons, so always stay slightly rich).

Note the info above is for the main jet only; which is the most important thing for a race bike, but with any road derived carb - I.e. from a GPX, you may well need to change the other jets and needle as well, as these affect part throttle openings and hence the "feel" of the engine - for this a dyno is really the only answer. If you do use a dyno then make sure that the operator has a good range of Kehein jets available for you to try before you arrive, as otherwise you will need to provide your own and plenty of them so that you can try different things out  (note that they are quite expensive so you don't want to be doing this).

Hope that this helps.

Techie

Responce 1

I used 140 jets and the bike is a huge improvement. I actually use the bike as daily transport (though it is ridden like a race bike) the motor is stuck in a stripped down RGV.  

Question 2

G'day. I am building a Supermono using an srx600 motor with some serious work done fitted into an RGV, my question is how much oil should I be building the oil tank to carry.  I am told about 2L's but this is a race bike and I have been told the more oil I can hold the better (for cooling purposes).
Any help would be appreciated .
Cheers, 

Jonathan

Answer 2

Certainly some people do use as little as 2 litres and previously I have used as much as 4 (due to the tank design and poor outlet positioning - to prevent oil starvation). The exact amount to use is hard to say. Personally I am going to make a tank that is as big as the space available will allow, so that I can alter the level, but ideally I would want to run with about 3 litres of oil mainly to allow
the air of the returned oil to separate out before being used again (to this end I would suggest fitting some perforated baffles inside the oil tank to aid this).

Regarding oil temperatures - check with your oil manufacturer on the web, but oil can happily run hotter than you would imagine. Also, note that the positioning and design of the tank and hose routings can make as much difference as the volume of oil (within reason) - i.e. in air flow and using aluminum for the tank material and a large surface area to volume design, etc. I would suggest that you aim for 3 litres and if you are in any doubt about the temperature then fit an oil cooler - even a small one in or out of airflow makes a large difference.

Sorry that this is a bit vague, but as you can appreciate each bike is different. Also, for the sake of an extra .8Kg for a litre, it isn't worth the risk to either starve the motor of oil (remember that oil surge due to braking/cornering etc may cause feed problems on a badly designed and/or low capacity tanks) or running it too hot.

Techie