1) The quick question: There is an amount of free play in the carb damper before the oil slows the piston rise. Why?
2) The longer version.: I have got twin HS4s on a 1310cc A+, AAA needles, Red spring. SW5 cam. When I got the car, it was running very rich, you could smell it, and see it on the plugs. However, it had previously been set up on a rolling rd, but it's remit had been max power (98bhp) rather than anything sensible I believe. Rather than take it to be rolling roaded again, I decided to spend the money instead on an AFR meter & put it on the exhaust near the gear stick recess. Works a treat. Sure enough, the AFR was reading 10-12 at idle, and still rich through to 30-50mph generally. 50-70, too lean at 16ish. I changed the needles to what I thought woukld be a better profie, AAB, and adjusted the idle to be a bit better at around 13. But was still too lean over 55mph. The worst thing though, was the lean spikes when just touching the throttle (at any speed, but worse at low revs and before warmed up) The lean spikes were causing terrible engine stutter, especially cruising at 20-40 & in traffic. Though generally the AFR reading was OK at that speed (14-15) I figured the lean spikes might be being caused by the free play in the damping, before the oil resistance is met. So I removed the circlip in both dampers, and inserted a small washer. It helped. I put in another washer. The lean spikes are almost gone, drives really well (overall a tiny bit richer too). I could probably tighten things up a bit more with a 3rd washer, and still leave plenty of room for the oil to pass on when the piston comes down. So why is there so much free play before damping occurs in the stock damper ? There must be a reason,.
I put a data port in the ashtray for logging, so I have graphs of before and after if anyone is interested.
