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.

[DBCooper]

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

Ain't it the truth. I have a cousin who's a gearhead, also gets off on speed, but he's a newest model BMW M5 - Mercedes AMG kind of guy. I can see his point of view but he doesn't have a clue about mine. None. I think it's a flavor of that old "cut your own firewood you're twice warmed" thing. To some there's pleasure in accomplishment and knowledge, to others the very same thing is just needless work.

[bobhasissues]

Perfect timing on your thread.
Just pulled my Dells and put on my old Webers last night.
Difference is night and day.
The Webers scream compared to the Dells, so now I need to figure what is wrong with my Dells. My current jetting is similar to your initial.
Our engines are somewhat similar. I do not have the benefit of an AFR, and am running a 494 cam but your findings will benefit me a great deal.
Can you share some more info:
What plugs and what gap are you running.
Do you know what emulsion tubes you are running.
What size accelerator jets.

[yeahmag]

Plug Gap: .045" I use an NGK plug that is pre-gapped to that.

Emulsion Tube: Stock ".2"

Accelerator Pump Jets: I don't recall, but I'll check soon.

[mrbubblehead]

aaron whats your timing set at? i settled at 35 degrees at full advance and my head temps went down 25 degrees easy. im using an svda dizzy.

[mrbubblehead]

your idle jets have good numbers. i wouldnt put the 62's in.... your mpg will suffer.

[yeahmag]

I run 12 degrees at idle, 28 degrees at 3500RPM (16 degrees total advance), and grey-grey springs with the Mallory. This seems to be the most universally accepted setup.

[ChrisFoley]

If you want your idle afr a little richer just open the idle mixture screws a tad.

[yeahmag]

Chris,

Thanks for the advice! This is with that goofy header of Evan Fullerton's that you helped both of us with back in the day. I've found with the last engine it backfired out the exhaust less with the idle circuit a bit richer. Not sure if I should care or not though. It runs great as is, just not at target AFR at idle and during transition.

I've worked hard to try and seal up all the leaks in that thing, but I'm positive there are still a few. Especially before it gets up to temp (slip joints are a bit loose).

The idle hunts ever so slightly as is, which would indicate a RICH mixture wouldn't it?

[yeahmag]

Time for a couple of updates...

Did a nice drive of about 25 miles at highway+ speeds, varying between 60mph and 85mph (3000-4000RPM). Head temps were 300-350F and again seemed to be fairly stable. I do feel like I'm getting a bit of "heat soak" for lack of a better term. At the beginning of the drive I was more along the lines of 300-325F where at the end of the drive I was averaging 325-350F.

My header is a leaky pig... I'm leaking at the slip joints on the collector, my header to collector gasket is leaking (again), and I found another pinhole in one of the primaries. I don't think I can trust my idle AFR's with this amount of leakage...

I'm considering playing with my timing a bit to see what effect i may have - the motor does feel fantastic though.

Finally, I added the Headflow Masters oil pressure control valve and it may have made few PSI difference at idle, but that's it. It does seem to control my oil pressures a bit better in general though and it's dead easy to install. I've ordered a voltage regulator to help stabilize the voltage to my gauges.

http://www.amazon.com/gp/product/B00BXDH9A...=UTF8&psc=1

[mrbubblehead]

ya you gonna have to fix all of your exhaust leaks before reading the af gauge. also you need to disable the accelerator pumps. they will change your readings. you will find that you should need very little pump squirt if any at all.

[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!