Originally Posted by coldfusion
Guys, just some findings at the track yesterday...
It could be many things that have gone wrong. I assume the clutch is set correct? If it's not, you could also overheat the engine when the clutch overheats causing the carb to overheat as well.
I also think that the head clearance may be too much with 0.4 mm shims. Check the total head clearance with shims. You should typically aim at about 0.5 to 0.6 mm at most for ideal performance. This may end up using the stock 0.3 mm aluminum shim or you may end up with even less at 0.1 mm or 0.2 mm to get you at those head clearance measurements.
Anyway, when you start to tune to race, always start with a small carb opening when the engine is idling at neutral position. Take out the carb insert and check the carb opening. It should be about 0.7 mm if I recall. A rough guide would be that the thickness of the flat tuning screw end should be the same as the carb opening.
Reset the needles to stock setting. Warm the car up about a tank or so around the track. Then start to race tune the engine. This is assuming your engine is broken in.
If you find difficulty in keeping the engine idling, try leaning the LSN bit by bit. You will come to a point where the engine idle will rise a bit. Stop and then richen the LSN by a 15 minutes.
Tune your HSN till you get crisp top end on the starter box first to get you in the ballpark. Slowly lean it bit by bit and try to listen to the engine revving. Put it on the track and try to run on the straightest part of the track. A few rounds and come in to check the engine idle and temp. Lean the HSN bit by bit and 5 minutes movements at a time. The engine should come in and idle should be steady and not idling erratically. If it is idling erratically, then richen the LSN. Test the engine out on the track till you're satisfied. Hope this helps.