Today I refitted the EFI having used a Hitchcock’s carb conversion for the last two years. Why? Well, I had become aware lately of a knocking noise just off idle. This and the issues I’ve had with vibration made me wonder if the ignition timing is right throughout the rev range with the later H carb conversion. In other words, though it fuels nicely with the Amal Concentric I’ve always been a bit suspicious about what happens to the ignition timing with the later conversion. The original one, which cost a lot more, came with a new generator rotor and ECU as well as all the carb mounting hardware and cables. This suggests to me that it had a new ignition map. With the later one it’s the same rotor and ECU as standard. So, does the ignition timing retard at tickover the have a nice advance curve or is in just fixed at full advance? I do wonder.
Anyway, having refitted the EFI, I started the engine, being somewhat surprised to find that the MIL went out
. Joy was short lived as I noticed fuel spraying from the pump joint. After sorting this with a better fuel clip I tried again. Success; it even ticked over nicely. Went for a ride and found that it was a lot livelier. This is partly down to the faster acting throttle. (With the H kit you use the same twistgrip. With an Amal this results in quite a gentle throttle opening as the drum is a bit too small to lift the slide in one twist of the wrist). Against this, there was too much slop in the EFI twin cables - adjusted when I got home.
I summary I don’t think I’d recommend the “Mark II” conversion kit. Whilst the fuelling is as good as you can tune the carb ( mine was fine as supplied) to me there’s a question mark over what exactly happens with the ignition timing. The exhaust I now have on my C5 is the road legal stainless one supplied by Hitchcock’s. It has a removable baffle but I prefer mine with the baffle. I imagine like this the back pressure is similar to the standard exhaust, though it’s a lot lighter, looks better and is better made. I doubt I’ll refit the carb unless an expensive bit of the EFI packs up.