Throughout my studying/reading up on Webers ( bought all available books and read posted procedures on F-Talk and the "other" site), it is obvious everyone has different opinions on how tuning should be performed.
I would, however, like to get something clear. During the tuning process, when you are at the point of adjusting the mixture screws, should you turn ALL mixtures screws by equal turns THEN listen how the rpms are affected OR should you turn ONE mixture screw, listen to engine rpm, get that one set, and continue doing each mixture screw independently (and each screw may happen to be turned by different amountsfrom the others to get the desired response)?
Theoretically, mixture tuning is the very last part of a complete tune. You should start with either or both a compression check and/or a leakdown test. You must have the plugs in good condition, wires in good repair, ignition timing set right, and the engine 'stinking hot'. Idle mixture control is so picky if these are not correct, attempting to adjust idle mixture is more likely to lead you off course than on.
The best way to tune the mixture is with a set of manometers, but since mercury is frowned upon in this country we need either a matched set of vacuum guages, a set of water/ATF columns, or a set of 'carb tune' columns to read the vacuum on each cylinder individually. As each cylinder sucks air in, a vacuum is developed in the manifold. These manometers measure this vacuum and allow you to see subtle changes in the performance of individual cyclinders.
With the engine hot, start with a lean idle mixture (all screws 1 to 1.5 turn out from closed) and 2000 RPMs or so. Now adjust the carb-to-carb throttle balancing screws for even vacuum readings cylinders 1-2 matched to cylinders 3-4 and 5-6 matched with 7-8. After these are matched, set 1-2-3-4 to match vacuum of 5-6-7-8. Now the throttles are (course) matched and we proceede to idle adjustment.
Drop the engine RPMs down to idle (around 1000 RPMs; 1050 for the F355). We now adjust each cylinder idle mixture to maximize the vacuum on that cylinder. Slowly turn the idle mixture (out since we started with a lean engine) and give the engine several seconds to come to terms with this new mixture setting. As you tune you may find that the engine RPM rises, This indicates the performance of the adjusted cylinder is improving! After each adjustment or when the engine has gained 100 RPMs set it back to idle RPMs. After maximizing the vacuum on all cylinders, go back and retouch the throttle settings (1-2 with 3-4::5-6 with 7-8:: and then 1-2-3-4 with 5-6-7-8) so that each cylinder is at the same vacuum setting (if needed).
To confirm excellent tune and balance; blip the throttle, the engine should respond with a crisp attack of RPMs at the very moment of opening the throttle. (e.g. no bog). In addition at the end of the blip, the engine should drop back to idle quickly and not undershoot idle.
If the drop to idle hangs and drops slowly, this usually indicates overall leanness, overshooting to too low an RPM indicated richness.
jrv did an excellent article about using colortune plug and a Daytona motor.
JRV (Jrvall)
Formula 3
Username: Jrvall
Post Number: 417
Registered: 11-2002
Posted on Sunday, December 22, 2002 - 4:53 pm:
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I'll go ahead and stick my neck out and post the General Steps I use, feel free to add, correct or flame these procedures.
Developing a Baseline for Carb Tuning.
1) Warm up engine, shut down, check compression, replace plugs
2) Check points, set dwell (clean, reset, replace)
3) Check Timing & Distrib Curve Accuracy.
4) Remove Air Cleaner, insuring nothing falls into throats, (install adapter pipe for fuel return line),
thoroughly inspect for fuel leaks, check choke cable adjustment and operation
(including linkage & adjustments on carbs), check entire length of carb linkage for
inaccuracies or link binding, with quality flashlight inspect all carb throttle adj. screws for regularity.
5) Start engine and warm moderately, noticing running speed & condition, insure idle is 900-1000.
6) check air flow at each throat and mentally note, shut down, loosen all linkage jam nuts (with exception of rear carb),
7) Insure all carb throttle stops are touching on their respective set screw, insure choke stops allow throttles to assume full rest,
start engine again and recheck air flow, if necessary raise or lower to match while insuring idle speed remains at approx. 1000rpms.
once completed shut down engine.
8) Once all above steps checked and completed remove 1st plug and replace with 'Colortune Tool,' restart, turn mixture screw all the way in,
slowly unscrew until light (color) appears, continue backing out mixture screw until orange color appears, turn slowly in until 'Bunson Blue' color obtained (as noted earlier the high end of the blue scale seems to work out the best),
shut down and proceed to next cylinder.....repeat steps on all cylinders.
9) Idle may have raised at this point, recheck air intake volume again, reset as necessary for match and correct idle speed (850-900 rpms),
shut engine down, gently tighten jam nuts, insuring not to move throttles off their stops, tighten front linkage with return spring attached, .
10) With engine off fully depress throttle to insure free operation, restart engine and test engine acceleration and return to idle.
11) If engine accelerates and returns to idle properly, let idle, check all intake air volumes once more to insure no discrepancies, and color tune second time to insure constant firing by slightly turning mixture screw in & out while carefully scrutinizing color to insure best operation.
*The above takes into account that the carbs and other systems are in otherwise good operable condition and merely need adjusting.
*In the case of any cylinder or carb that doesn't have a nice stable range of adjustment the cleaning & adjusting of the internal components will be necessary.
*In the case of Carbs that fail to adjust properly, a host of problems can exist. If it's determined a carb cleaning/rebuild is in order, while the carbs are off
it is recommended that all intake Manifold O-rings are replaced, carb bases checked for flatness using a straightedge, all warped/deformed bases flattened by machining, carb bodies thoroughly cleaned and dried, all jets inspected, sized and noted, base gaskets replaced, needles & seats replaced, accelerator pump diaprams replaced, float levels carefully and accurately set, internal carb check balls checked for sticking, carbs reinstalled
and above Procedures repeated.
* When using a colortune it is best to try and check and adjust individual cylinders as quickly as possible, due to the lenght of time it takes to insure accuracy it might be neccesary to allow the engine to cool down occasionaly. However, haste makes waste and a methodical approach addressing anomolies as they are uncovered is a sound approach.
Leaning about carbs is good
Learning about misconfigured carbs and how to correct them is better
Adjusting misconfigured carbs on a old crap car is good.
adjusting misconfigured carbs on a Ferrari is good but you should know what you are doing before hand.
adjusting perfect carbs on a Ferrari "for practice" is just plain dumb.
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Hi,
Throughout my studying/
Linear Mode
