The Tweaking Begins

It's surprising how quickly 600 miles have been racked up in the cobra, just from a few trips around the local villages on the back roads, pootled to work in the frost/ice (that was interesting!) and a few other short journeys when the weather has allowed. 

Following the Christmas drive when it was running quite badly, I bought a vacuum gauge and adjustable timing light. The engine info from BAE said the engine should have 36deg "all in" timing at 3000rpm. It was set purposely retarded for run in. I measured this at approx 24deg all-in, static timing was about 4deg so total centrifugal advance is around 22deg. The engine came with no vac advance fitted, dizzy is a newer style HEI with module built into the cap. 

I went for 20min drive to get everything warmed up then set the timing to the 36deg all-in figure, which would give static timing at about 14deg but I forgot to measure and check this. The car re-started easily when warm but the morning after it kicked back against the starter so I had to back off the timing to 32deg all in and it seems fine now.

Using the vac gauge at idle I was getting 9-10in.hg at idle which is pretty low but my cam is pretty big, comp cams xe284h with following specs:

Advertised Duration		Duration @ 0.050		Valve Lift W/1.5 Rocker		Lobe Sep. Angle	RPM Operating Range
Int.	Exh.	Int.	Exh.	Int.	Exh.
284	296	240	246	.507	.510	110º	2300 - 6500

Knowing that my idle set-up was pretty crap, I set it back to "stock" according to the Edelbrock carb manual. It advises that for a reasonable setup when trying to get a new carb to run, you wind the two mixture screws in until they bottom out, then out 1 1/2 turns, then this is your base setting. I did this and immediately saw better vac and the revs rose. I backed off the idle speed screw to get the revs down to about 850 but its hard to tell exactly what revs as the needle isnt steady. I ended up with the mixture screws out roughly an extra turn which gave peak idle vacuum of almost 13in.hg but again this value wasn't steady but probably due to the cam and varied by ±0.5in.hg.

Went out for another drive and it was a little bit better but still lurches and kicks a bit below 2200rpm so I'm wondering if the idle throttle position is still slightly too large which will uncover transfer slots etc that I'm still learning about and trying to understand.

More fiddling required, next stage is wideband O2 sensor to see if I can home in on a better idle mixture setting.