Engine misfire ...

[firehawk]

Hmm, I have a similar setup with 44mm Mikunis and the standard ECU for ignition. Do you have the TPS and MAP plugged into the wiring loom but not connected to the throttle shaft/vacuum?

I had problems with misfiring at first when I had the MAP connected electrically but not into manifold vacuum. The ECU didn't provide enough advance at above 3500rpm and I had fire spitting out both from the carbs and from the exhaust. The hotter the engine got, the worse the misfiring became. Providing vacuum, albeit only from cylinders 1 and 4, to the MAP sensor fixed the problem. The same problem also occurred when the CEL is lit due to missing sensors and the ECU falls back to base advance (~10deg BTDC as standard) only.

If the TPS is connected into the loom but just dangling there, the idle switch is always closed and therefore the ECU uses only an extremely simple advance map intended for overrun and idle. Locking the TPS to a slightly open position would put the ECU off idle and and into the actual advance map.

To get rid of the CEL and error codes, I have modified my ECU with a few resistors so that it sees a constant +20C intake air temp and a ~80% throttle input. It has no pin for O2 sensor and uses the idle mixture pot instead but similarly, the O2 sensor also has effect on the fueling only when on idle. Off idle, the ECU only considers RPM and MAP when it determines the ignition advance so static readings from the other sensors doesn't really matter. The ECU is happy as long as the sensors return a sensible voltage/resistance