1018cc wrote:
It is very useful Simon. I have been helping Tadhg with mine. He has a 1310, big cam, race headers, AEG163 head etc etc etc but with a pair of HS2s. Multiple people told him yellow springs, WinSU told him yellow springs but when I put the borescope down the carbs the yellow springs were only letting the dashpots raise approx 5mm at WOT/redline. After swapping around springs, it actually needed blue springs. The process of finding what damper oil to use and what needles had to start all over again.
Nick's been brilliant with this. I've learned a LOT playing with his borescope and AFR setup. Think he's learned a bit, too. He did at least learn his HS2's are running blue springs. I bought yellows, and I had reds. I'm now on blues. Between a MegaJolt (which gives MAP and advance), the borescope and AFR, I don't see how you could tune any better, especially given it's real world testing, which is hard to simulate on the dyno. And not cheap, and hard to schedule... Nick can get out and tune his cars at 5am or 11pm.
Nick's right, set your spring before you set your oil. And, for mine, you should set your needle before you set your oil. Oil is the last piece in the puzzle.
Your spring should have the piston fully raised no more than 500rpm before peak torque. When Nick says 'the full length of the needle', just remember that SU needles vary in length. So don't try to measure it. The best measure is that the piston rises so that it's completely clear of the throat of the carburettor. I phrase it this way because my car runs M's, Nick has GY's. GY's are 3 or 4 stations longer than M's, but a HS2 (both cars run HS2's) can't use the extra stations on the GY - the piston doesn't rise that far.
Your needle should give you good AFR's at all stations on steady throttle - at idle, low cruise, high cruise - and under full acceleration (high revs).
Your dashpot oil should hold your piston down just enough to stop you going lean under load/acceleration at all speeds under peak torque/full throttle. If you've got a stock setup, which uses a stock needle, then stock oil will be right. If not stock, it's trial and error...
My thing's still not right. WAY better than it was, as good as it can be with the other hardware. But I now know that the problem's even further up the chain... I started out trying to set a needle, when I didn't have the right spring. And it turns out I've got significant issues with exhaust reversion, caused by having too large an exhaust. This is something Matt Read cautioned me about 9 years ago - but I couldn't argue the cash to fix it... Proof is the carbon build up on the back of my inlet valves. Headers are ex-ReadSpeed, 1963, speedway spec. HS2's were fully refurbed over Christmas, with custom stub stacks, spindles thinned, throttles knife edged, bores smoothed, pistons bevelled. So they're pretty well fully Vizarded, and I'd guess are close on a HS4 for flow. And the engine's 1301cc.
When I can get to fixing the mismatch in exhaust to the rest of the engine, then I can re-start the process of picking the correct spring (which I'm expecting will be heavier than blue - when there's actual vacuum in the inlet manifold), then the needles, then the oil...
