Check a few basics first:
Make sure the Mychron / Alfano is reading correctly. Remove from kart and put the sensor in a pan of boiling water – should read 100 degrees or thereabouts.
Ensure that you are using the correct mix of petrol / oil. Should be 3% Shell M ie 30mls oil per litre of standard / super unleaded petrol. Make sure it is mixed well and filtered etc. before putting in tank. If the weather is particularly hot, then you might increase the oil by a small amount.
Check sprocket / chain alignment. Lubricate chain well.
Make sure rear axle bearings are running free. Check that chain is not too tight – 1cm play in upper chain run with no ‘tight spots’. Ensure that driver is not ‘riding the brakes’ when going round (usually knackers the clutch….!) Set gearing for max revs of 12000 - 12500
Normally expect to see approximately 100 degrees plus ambient temperature after 3-4 laps. In warm weather, use 31 Denso plug; cold weather use 27 Denso plug.
Increasing temperature can be an indicator that the kart is ‘bogging down’ through corners. Lower the tyre pressures and / or adjust front end to promote lift on the rear inside wheel. Use short rear hubs and move the hubs outwards if possible. Loosen off side pods and rear bumper. Use softer rear axle.
Sometimes, richen the low (rear jet) by 1-2 ‘seconds’ (0-60 on clock face) – screw the jet out anticlockwise to richen, clockwise to lean. Only use small changes.
Never really found a huge correlation between the head temperature reading and lap times, but tended to use the 31 plug when air temp was above 15-20 degrees and the 27 plug when colder or in wet weather.
The Iame does not seem to be quite as temperature sensitive as the Comer used to be and is far less likely to seize - however I stand to be corrected on that one !!
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