[Burdekin]

Bit of an update had a bit of a play with the ignition curves; B20A it didn’t like, I was recommended giving the B18B curve a try and it now goes nice. Currently about 17deg at 1500rpm so will try 19deg and see how it goes.

I then thought I’d swap the metering needle over in the carb so ordered a new B1CC needle thinking that was what was in the carb and it didn’t like that at all at idle. I never changed the jet. Originally I found out it was fitted with a B1AN needle. I then thought I may as well fit the adjustable jet I bought previously and rebuild the carb so that is what I did. I used the body of a spare one I had as the original had some wear under the diaphragm area. After the rebuild I tried to use the colourtune I had sitting at the workshop and I didn’t get on with that at all so I used my mulitmeter to help set idle mixture. I lowered and raised the jet until I found the position where the jet was at its highest position with the highest rpm; lowering it more richened the mixture but did not increase revs. I also replaced the cracked carb isolating block, new hoses, clips and brake booster NRV and seal to ensure I had no vacuum leaks. Set idle at 800rpm and she idles lovely.

The engine goes well and next I wanted to check the air fuel mixture when driving and idle so I dug out my old wide band sensor. It is quite old and basic and new ones give a numerical display so I bought a new one and welded in a boss in the exhaust. Did some testing with the standard filter and my K&N filter with stub stack. Firstly the standard, idle was spot on for a Stromberg/SU about 13.2:1, cruising speeds was again spot on between 14 to 15:1, over 75mph and it starts to lean out at about 16.5:1 and wot it goes to 12.5:1 but then leans out to 13.5:1 pretty quickly. The K&N filter arrangement was similar but probably 1/2 point leaner. I’m running 80/90 gear oil in the dashpot. All totally acceptable but above 70 and wot could be richer so I thought I’d like to try a richer needle through most of the range but a good bit richer at the high end. Hopefully this matches the K&N and stub stack better and gives extra performance. For my Stromberg there are 53 needles to chose from so I typed them into a spreadsheet and compared and plotted them against the B1CC needle and the one I want to try happens to be the B2AF which was fitted to some earlier B20As. And that is where I’m at, just waiting for the new needle. I’ll then see how it goes with the wideband and if okay I’ll then do some 0-60mph runs and compare things.