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post #1 of 12 (permalink) Old 02-12-2017, 06:00 AM Thread Starter
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carbs spitting

Good morning guys, I need your help please.
I did a 2L build with an 83 block and head, european 2L manifold, weber DCOE, motronic pistons,
IAP 306 11mm cams, don't think I have any air leaks cause everything is new, but the carbs are spitting mostly between 2-3K. Set the carbs according to pierce manifold suggestion after I gave them my specs. Here's where I'm at with settings please let me know if anything seems out of wak.
lash ..010 for intake .012 for exhaust
cam timing 104/104
timing mark at F at 800rpm
123 ignition
main jets 140 primary 33 or 36 (not sure, will check w/pierce on Monday
air correction 185 secondary 4.5
emulsion tube F11
idle jet 50F9
pump jet 40
pump exhaust 50
needle and seat 200
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post #2 of 12 (permalink) Old 02-12-2017, 06:13 AM
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Fuel mixture is too lean probably caused by too small idle jets regarding your carb intenals.

Which DCOE´s are you using ? 40 DCOE xx ?
Suffix is missing but very important. Depending on carb´s suffix also emulsion tubes could be wrong. If you have 151´s right out from the box, then your chokes would be 30´s which are too small for a 2 liter Nord.

Ignition timing advance probably could need some more degrees than "F". Which 123 ignition curve have you set ?

At the end you´ll not get it right without using an AFR measuring device like Zeitronix. Ed surely will chime in with more input on it, I guess.

Last edited by hunttheshunt; 02-12-2017 at 10:50 AM. Reason: Corrected typo
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post #3 of 12 (permalink) Old 02-12-2017, 07:15 AM Thread Starter
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The carbs are DCOE2-31874 & 30513, my spare Venturi are 33 so I'm 99% sure the new ones are 36.
The 123 setting is alfaholics low altitude setting and yes I thought of advancing a bit more but did not try yet.
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post #4 of 12 (permalink) Old 02-12-2017, 07:27 AM
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Spitting back can be caused by cams with too much overlap but I have no data on the IAP cams.
Alfar7 has reported that machining is required to correctly match a Euro manifold to an L-Jet head. Are you sure that you have no air leaks?
As Sir James said - what curve are you running and what is the advance at 5000 rpm?
Carb settings look reasonable but 36 venturis are large and will cause a delay in the main circuit which could result in a lean condition at mid rpm.

Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke

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post #5 of 12 (permalink) Old 02-12-2017, 07:47 AM
Richard Jemison
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Cams

Actually those cams measure 10.5mm lifts.
If you set the exh cam at 104 to 106LC with the intake at 102 LC that might solve the spitting that is commonly caused by excessive overlap.
If it still spits move the intake to 104.

These cams will probably do better with 33mm venturis, or if the 33mm venturis are stock Weber pieces, reshaped to 34mm with a true & correct "Venturi" design. That should improve drivability.

Ed, you should conller 45 DCOE venturi send them and I`ll correct them to try.
Rj

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post #6 of 12 (permalink) Old 02-12-2017, 07:49 AM Thread Starter
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no I'm not 100% sure that there are no leaks but I guess I could start checking for that.
As far as the curve I'm not sure how to give you a value as I purchased it from Alfaholics and they preset the curve.
Also as far as advanced timing at 5,000 I forgot to mark the pulley prior to reassembly and did not realize that pulley for L-jet engine does not have M mark.
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post #7 of 12 (permalink) Old 02-12-2017, 08:00 AM Thread Starter
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Hey RJ, the venturis I took off seem to be reworked because they do measure 34 and the stamping is no longer there. Also I did get these carb from Florida form Terry user 459 perhaps you did them already.
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post #8 of 12 (permalink) Old 02-12-2017, 09:50 AM Thread Starter
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I installed 34 venturi and advanced the timing a bit just before the F letter, running a bit better but spitting only from #2 now. I'll check fuel level again because some fuel came out of venturis.
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post #9 of 12 (permalink) Old 02-12-2017, 10:43 AM
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First, try 55F8 idle jets and see if it's better or worse. Early on in this thread mixture was discussed. Also try the F-16 emulsion tube on the HS circuit with 135 main jets and 190 air correction.


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post #10 of 12 (permalink) Old 02-12-2017, 11:35 AM
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"spitting back can be caused by cams with too much overlap"

Not surprised. When I had my 67 Austin Cooper S modified by Downton Engr to 3/4 Race setup, the SU carbs would spit out fuel below about 2800 rpm because of the cam characteristics. Common problem for such cams it seems.

Lived with the spitting. For street driving, used air cleaners to smother the gas spray; for competition, used air bells instead for better and smoother intake airflow.

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previously owned since 1964:

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Last edited by Del; 02-12-2017 at 11:43 AM.
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post #11 of 12 (permalink) Old 02-12-2017, 12:21 PM
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Quote:
Also try the F-16 emulsion tube on the HS circuit with 135 main jets and 190 air correction.
I tried F11 tubes in my 45DCOE's instead of F16. They were significantly leaner at the top and I had to go to bigger main jets and smaller air correctors and then the AFR was too low at 4000 rpm. F16's certainly work better in my setup.

Ed Prytherch
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76 Suzuki GT500

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post #12 of 12 (permalink) Old 02-12-2017, 12:22 PM
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Quote:
Ed, you should conller 45 DCOE venturi
Can you elaborate on that?

Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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