Firehawk's N2 racecar project

[firehawk]

Ok, finally the engine is starting to run a bit like it's supposed to. Without ignition advance, it started and idled nicely but didn't really pick up revs at all. Now that the advance works, it both starts and runs properly.

I hacked together a quick'n'dirty method for gathering enough vacuum to provide the standard ECU a MAP-signal. As mentioned earlier, the ECU itself is modified slightly to overcome the lack of a TPS, air temp sensor and the idle mixture pot. These have no function on the ignition side of things so just faking them with two-resistor voltage dividers works quite well. The ECU does throw error code 11 when the diagnostic plug is connected but this is completely harmless as it only indicates that the idle switch was open on power up (the switch is normally inside the TPS).

Since the TRD intake manifold only provides vacuum ports from cylinders 1 and 4, I took those two, connected them with a Y-junction and ran a small hose via a filter to the MAP sensor. This seems to work reasonably well and the ECU runs the car with the stock ignition advance map. Since the fueling is performed by the carbs, the slight "jumpiness" of the vacuum doesn't matter as much as it would with ITBs+injectors.

Now that the ignition advance works properly and the engine starts to burn the fuel earlier, I found out that the carbs are way too lean. The engine idled very nicely, at a stable 850rpm but when carefully pressing the throttle, the carbs spat puffs of smoke and the exhaust popped and crackled loudly. On the other hand, the acceleration pumps seem to work exceptionally well with the 40 nozzles as a fast dab of the throttle picks up revs very sharply without a hint of hesitation.

A friend of mine shot this video while I tested the throttle response and tried to peek at the smoke-spitting carbs through the gap under the raised bonnet.

http://hanza.1g.fi/kuvat/sekalaista/corolla.AVI

Even with the muffler I added, the exhaust is ear-piercingly loud and on the video it's hard to tell when it backfires because the camera's mic gets completely swamped. Also, the recently applied heat-resistant paint on the muffler started to emit an acrid smell and white smoke towards the end of the video.

Anyway, since the engine ran so obviously lean, I pulled the 52.5 pilot jets and 135 main jets and skipped two sizes on both and replaced them with 60.0 and 150. No more backfire and the engine still revs quite eagerly. It may have gone a bit too far into the rich side but I won't know that for sure until I get to do some actual full-throttle driving. Gotta bleed those brakes first.