Jet Black

[tek]

Jet black is the color of my plugs just a few minutes into running. After checking for air leaks, etc. I did the setting according to Dave Andrews' article "Selection and tuning of Weber DCOE Carburetors" posted elsewhere on this forum. It appears the whole problem is with the jetting combination. I have no idea where this setup came from, but I have a suspicion that many years ago someone simply plugged in a set of Webers from another engine, probably a larger displacement. So the engine runs super rich, and I can't lean it out.


I live at about 3,000 ft above sealevel with average humidity about 30%.

Using a weber jet calculator I downloaded from www.alfabb.com, it appears I will have to change out nearly all of them.
The existing setup seems to be more for all-power for a 1600 to 1750 at sealevel. I want to lean it out for flexible performance and best mileage. My engine is the 1290 cc , Junior with 40/28 Webers


Existing setup:

IDLE JET 50/F11

MAIN 110/F16

PUMP 35

AIRCORRECT 220

CHOKE TUBE 28



Proposed setup:

IDLE JET 40/F9 (would the existing f11 work here?)

MAIN 100/F11-F15 (would F16 work here?)

PUMP 35

AIRCORRECT 150-160

CHOKE TUBE 25(flexible) -27 (Power)



I was going to replace only the idle jets to see if that would do it. But those 220 air correctors seem way out of line too, Could the air correctors be responsible for the over rich mixture? I ask, because the existing setup for All Power seems about right except for those air correctors. But I tend to think the whole setup is just too rich. And now with the price of fuel...well...
So as it is, I'm getting a quote from webercarbs direct for what THEY think the setup should be.
I'm posting this so I can get a second, probably more accurate opinion, from you guys.
Thanks for your comments.

[60sRacer]

What plugs are you using? Alfa tended to use pretty cold plugs on the carb cars - Loge 2HL was common, and I always had black soot deposits for minor local driving; only got good plug color on long or hard-driving excursions.

At altitude, you will be rich with the stock jets as well.

Robert

[tek]

It came with Champions. I ran those and some NGKs, and some Marine plugs that were pretty hot. It's got E3s in it now and the problem is unchanged. Have good spark with the standard ignition. I'm rechecking the timing today, but am going to the leaner setup.

[101 Alfa Mike]

Assuming the car runs good with the current jetting, I suggest you concentrate on the idle jets. If you doubt that advice, take a short test drive with the main jet stacks removed to get a first hand feel for just how much driving is done on the idle/progression circuit.

40F9s might be just the ticket, but I'd probably wimp out and try some 45F8s first.

Mike R

[Alfajay]

Tek:

You had written: "But those 220 air correctors seem way out of line too, Could the air correctors be responsible for the over rich mixture?"

It is my understanding that air correctors do just that - they add more air (at full throttle) to correct for...well, something. So, unlike main and idle jets, larger numbered air correctors will add more air, resulting in a leaner mixture. Again, this only applies at full throttle, so it may be irrelevant to your sooty spark plugs.

Another thing that I have learned about Webers is that the advice of Dave Andrews, WeberDirect, the BB, your local guru, etc. is helpful as a starting point, but you still need to "dial in" each engine. Your 3,000 foot altitude will also result in different final settings than jetting.exe would suggest.

[crashmctavish]

Try driving at sea level & do a plug chop with the motor hot. Your altitude is the main issue. What octane fuel are you using?

[tek]

Driving at sea level is not an option, so I ordered the jets and tubes as indicated by the jet program. Basically, it calls out all the leanest settings and I think that'll give me a comprehensive setup. Then if I'm not happy with the way it runs, I'll at least know I've got a system match for all the elements.

Also, initially I did not understand exactly how the emulsion tubes were categorized, and that is still a bit of a question. But the F16 tube has an orifice value of .181, where the F11 is .031, about a six fold difference without any geometric conversion. Along with the 220 air corrector, it seems to me that this might actually defeat the purpose of the tube. Rather than producing an emulsion of fine bubbles temporarily suspended in the fuel it might produce big bubbles which could quickly percolate out of the mix. Add to this the small 100 or 110 jet size, and it seems that the emulsion might be stalled ahead of the jet, causing the bubbles to perk out completely. This would result in an unemulsified stream of pure fuel, which would not disperse or atomize correctly causing a wet fuel condition ahead of the valves. And that is exactly how the engine feels and acts.

This would be similar to the relationship of the choke tube air velocity and the fuel stream. Too big a jet , too slow the air, too rich and wet the mix, especially at low rpm. I should have the jets and tubes in a couple days, and I expect there to be a dramatic change. I'm hoping that the leaner mix might actually enhance performance.

We'll see. ayone else want to weigh in here? Papajam, you still out there?

[crashmctavish]

Thats sounds right mate. Altitude compensation has an surprising effect. Two stroke motorbikes wheelie like crazy on frosty mornings because the air is denser. Take one over the swiss alps and they play up, run rich & cough like crazy, snow is on the ground but the air is thin. Aircraft pressurise their cabins at 10,000ft so the passengers stay awake! 3000ft is nearly a third of the way there, when you have the jetting right run high octane for a bigger bang.

[tek]

I've been running 91.5 Octane, thoughI found no appreciable difference running 85.5. When I had a GTV in 1976, I think I ran 93-96 octane, which is probably more like what it should be running.
I have access to some 110 fuel. At 3,000 feet you have to use it up quick or it just evaporates. And now at around 8 or 9 bucks a gallon, I'll probably tune for pump gas, and throw in some octane booster.
By the way, what kind of fuel mileage have you gotten with your Alfa? It seems to me that my 67 GTV got something over 25 mpg when I drove it sensibly.

[101 Alfa Mike]

The Weber Tuning Manual has an altitude correction table which suggests multiplying the stock main jet size by .95-.97 for continuous operation at 4900-6600 feet. It seems that the correction at 3000 feet would fall within the normal "dial in" range for individual engines.

Speaking of individual engines, are you running the stock cams? If so, you may want to return to the stock jetting for your starting point.

Mike R

[tek]

Since the smallest main jet is .100 , that .95/.97 conversion works about right if the stock mains were .110
at 104.5 to 106.7 . So a 105 might be appropriate too. I'll run the 100's and if that's too lean, I'll put the 110's back in with the f11 emulsion tube. Running a tad rich is less dangerous than too lean.

[papajam]

I'm assuming valve clearance, cam timing, dwell, ignition timing, compression, float levels, fuel pressure, etc. are all good?

If so then you're not far off at all since your current carb jetting is stock for a Series 1 & 2 1300 Junior (except for the main jet; 112 stock vs. 110 now).

Do the plugs turn black when the engine idles, under part throttle, under full throttle or any combination? The reason for asking is because when the plugs turn black determines what may need adjusting.

[alfaparticle]

You are running rich with standard jetting so I would suggest that you check the float levels. Also, what kind of fuel pump are you running and do you have a fuel pressure regulator? The carbs will flood if the pressure is too high. Are the venturis wet?

[tek]

Right now I am operating on a number of assumptions. According to the PO, the engine was completely rebuilt in 1985 by a german tech/engineer who was hot on Alfas. The PO also told me he drove the car a couple hundred miles at the time and it performed excellently. Subsequently, the car was put away in 1986 until the summer of 2006 when I found it. So initially, I have not touched anything internal. I replaced the points, coil, and plug wires. With E3 plugs, I have a good blue spark.

The engine runs rich whether idling or cruising. High RPM at road speeds does not clear it up. And even after 20 miles or so of road driving at 75-85 mph, the plugs are so carboned that they get wet at idle and have to be cleaned. And I get sooty exhaust under acceleration, or idle. Once the plugs get dirty, I can hear the fuel dribbling at the valves, like pouring fuel down a four barrel trying to keep a v8 running.

So, I'll plug in the new setup and then analyse it further. Tell me what you think about existing setup with the 110 jet, f16 tube, and 220 air corrector. That just seems way out of line for a 1290 cc engine.

Regarding float levels: I did what you suggested Ed in your postings elsewhere. Instead of a nail, I used a 6" digital caliper, setting the base of the slide on the top of the cover plate rim, and measuring with the slide rod down to the top of the fuel in the main jet cavity. It was on the high side , 1.70 inches or so(or whatever your figured in the post were) , and we adjusted the fuel level down to about 1.88. That did seem to help a bit. Maybe I'll have to take them down a bit more.

[tek]

I'm running a stock mechanical fuel pump.