It's been nearly 10 years since I started the engine project, so I've gone back and updated most of the missing photos. I've also got a summary of the last 3 years below
When we left off in 2021 the initial Cooper S twin HS2 carbs were sold and I was running the Dellorto DHLA again. I was still getting the intermittent pinging at around 3000rpm at part throttle.
I stripped down the Dellorto, checked over everything, added a new bearing seal to the spindle and sealed all the manifold threaded ports. I also added a soft mount kit (the type with the rubber O-rings). Overall this helped a little, and the carb was much cooler as the soft mount kit also acted like an isolator.
I had a reoccurring fouling on #4 spark plug, so bad that it'd foul up while driving. After a bit of searching I found one of the screw in spark plug leads wasn't making decent contact. With some modern push on leads it was running nicely again
In July 2022 I had another head gasket failure, again between 3&4
When I'd had the previous failure in 2020 I'd used my spare copper gasket as there wasn't much in stock at the time. It was a very similar failure to the previous cheap copper gasket in 2020. Once I got the engine running again I noticed the base timing was 20 degrees, which would have put max timing at 40 degrees. I have no idea how it had got to this point, normally I'm pretty careful with the timing
While the head was off this time I gave it a good clean and decided to check the volume of the combustion chamber. They measured up at 24.6cc, so with my flat top pistons, 1100 bored out 080 over & a couple thou deck height the compression ratio ended up about 11.2:1 . This is quite a bit higher than I was expecting, but it does explain the issues I had getting an appropriate timing curve & the intermittent pinging
This time I was able to find a Victor Reinz head gasket. It lined up much better between the 1/2 and 3/4 cylinders and doesn't overhang the bores which is an improvement on the previous ones I've been able to get
While this was all apart I had an O2 sensor bung added to the manifold, so I'd get better readings at idle.
It was back running again now, and with the idle mixtures able to be read on the gauge I started adjusting the idle mix screws and jets to get the reading better. BUT - still getting the 3000rpm pinging
I made some adjustments to the dwell setting on the blackbox to increase the dwell time and increase the spark energy. This helped to some extent, but didn't solve the problem. Next I changed it to 60 degrees at all RPM points (the same as a points system) and there wasn't any improvement
Initial dwell setting
After
Now we are up to 2023:
I just kept having problems with the Dellorto keeping the mixture under control. If I put in a lean idle jet I'd get excessive bogging to the point it was hard to drive. With a richer idle jet it'd drive around at 10:1 and foul up the plugs. I couldn't get a decent middle ground. I stripped and checked the carb another few times but I couldn't see anything obvious, so I'm going to get it checked out by someone else
April 2023 I lost a core plug on a MITG drive and had to get towed home. I've since replaced all the core plugs. At this point I took off the Dellorto and sent away the chokes to be resized (in hindsight a rebuild would have been a better option) as I was just sick of how it was driving
I had bought some dual HS2 carbs on a Peter Manton manifold many years back and decided now was the time to rebuild them and use them.
The dual HS2 drove really nice! They were smooth, quiet and had a very good throttle response from idle. With a few days of tuning it was driving perfectly, good pickup from idle and cruise mixtures were exactly where they should be. However there was a significant performance difference compared to the Dellorto
Next up the HS2 carbs started running really weird, and they'd go full lean on the gauge while idling. I did all the usual checks and couldn't figure it out - so back on with the Dellorto! But then the Dellorto had the exact same super lean running. I ended up stopping around the corner from home when the fuel pump stopped. The wiring was very poor and it'd been starting and stopping the pump. That explains why both sets of carbs were running super lean!
So now with the fuelling mystery solved and the Dellorto still running poorly I put the HS2 carbs back on again (which is how it is today). It runs fine, a liitle rich on full throttle but otherwise ok. However the 3000 ping is still there
Getting to December 2023, I swapped from the standard 3.0ohm coil to a 1.5ohm coil (a Bosch SU12R). This coil makes approximately double the power, so to make sure the remainder of the system can cope the dwell curve was updated to a setting of 27 degrees at idle to a max of 60 degrees at 5000rpm. I have noticed a slight improvement with the extra spark, it'll run cleaner at a leaner mixture and starting performance is slightly better too.
During 2023 I regained my appreciation for SU carbs so I decided to track down a HIF44. While the dual HS2 have been good, with the Manton manifold they are restricting performance and obviously there is twice as much to tune and make sure it's the same side to side. I figured the most simple thing would be get one single big carb.
This carb came with a Metro manifold and all the brackets to work on a mini. I've since got a gasket kit, some extra needles, throttle cable etc and hopefully this will be ready to use soon. At this point of the project I just want it to work and be reliable as I've definitely spent more time off the road than on in the past few years due to various issues.
At this point I'm still getting a ping at 3000rpm on part throttle, despite only 15 degrees of timing and rich mixtures. I think at this point the only cure will be reducing the compression ratio down to an acceptable level for 98 octane fuel. I've tried everything I can think of and it's the only thing left. My ideas range from:
Double head gasket
Send the head away for modification
Machine a dish in the pistons? (There’s no other choice in +080 than flat top)
Get a 998 crank and pistons