Dellorto Tuning, for head temps and power Options

[yeahmag]

The new motor is fully broken in by now, so I've started tuning. For reference it's specs are:

2056cc
AA 96mm P&C (5+ years old now) balanced
Raby 86A based cam
2L heads with SS valves and dual springs. Cleaned up and fly cut.
Stock rods - balanced
9.5:1 CR
Mallory Unilite (grey-grey, 12-28)
Mallory 6AL (6500 RPM rev limiter)
CB Dry Sump pump (very massaged)
4:1 header (1.5" primaries with 2.25" extend secondary and Phase9 style silencer)

Gauges:
Innovate LM-1
Aircraft Spruce M1000 CHT
VDO Oil Pressure and Temp

Head temps were always great when wide open, but fairly warm when cruising and rich at WOT. Idle seems a bit lean too. Seemed to cruise at 350F-375F on #3 and 3K RPM. Nice and cool around town. Initial configs:

40 Dells
34 vent
180 air
140 main
60 idle
2 turns out on idle volume adjusters

Initial change to a 200 air to bring the mains in a bit sooner. That brought the 3K RPM cruise head temps down to 300F! Perfect! But as I started cruising closer to 4K RPM (80+ MPH on a hot day) head temps climbed and the AFR leaned out. I also noted that while I was no longer pig rich at WOT I managed to go a bit to lean. Next change was to a 145 main.

The 145 main seems to have had a very positive effect. The car is FAST. AFR is 12.5-12.7 at WOT and I'm cruising around 14.5-15.5. I need to get it out on a long highway drive to see head temps, but I expect positive results.

Idle seems lean (16-18 AFR). While I'm not popping and snapping I think I could stand to throw my 62's in there. I imagine the AFR is a bit skewed at that low of RPM due to reversion, but on the other hand you have to wonder if the Mallory 6AL is covering up some of the lean mixture. No head temp issues, at those low speeds (250F), but I'd like to keep the AFR readings on the rich side of 16:1.

I love this stuff... There is also something very satisfying about reaming your own jets.

[yeahmag]

And now for some more updates.

Instead of getting to go to G&R I had to rebuild my carbs and what a difference it made! The car was dropping cylinders and acting all kinds of strange. I was sure I had ethanol gel in the float bowel again. What I ended up finding was that the floats were grossly misadjusted. Equal, but misadjusted. They were set something like 0 closed, 5mm open. Way, way up there.

After setting them at the recommended 5mm closed and 12-13mm open the car runs like a dream. The low speed AFR is much more consistent. The idle volume screws went from 1.5 turns out to 3+ turns out (in line with the CB Book recommendations) and my head temps are rock solid. I need to get it out on the highway still and go for a long drive, but it's a completely different car.

Symptoms that went away:

* Idle "dive" under hard stops.
* Popping and banging under decel
* Briefly loosing a cylinder under very light cruise (intermittent)
* Wild, unpredictable swings in AFR (I always thought it was my LM-1/exhaust leaks)

I'm sure I went through these several times by now, so I'm a bit concerned that it might be metal fatigue at the floats. But, now when and if that strangeness starts again hopefully I'll remember back and know what to check!