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Carb tuning question

68 2.0S with webers. I tuned the carbs at 80 degrees and have always ran the car around this ambient temperature and it pulls hard. This morning took it out early at an ambient temp of 57f, car wouldn't pull well until 4.5 or 5k. I don't have the heater tube to the air intake, never thought I needed it. Are the webers that sensitive to temperature, do I need to add the heater tube or just adjust the idle mixture screw a little. If idle screw 1/4 turn in or out?
Old 07-14-2017, 05:11 AM
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1/4 out richens it up
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Old 07-14-2017, 06:35 AM
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Air is denser when cold, you might have been slightly lean in the morning if you tuned it in hot weather.

I richen the mixture as much as the plugs allow. I suggest checking the plugs and turning the screw out a little and rechecking until you get the mixture and power the way you like it.
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Old 07-14-2017, 07:40 AM
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Checked the plugs, cleaned them and adjusted idle mixture accordingly. It now pulls hard again but not sure for how long so I ordered a Colortune to get the idle mixture perfect.
Old 07-17-2017, 06:42 AM
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what happens when it's back to 80F tomorrow morning?
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Old 07-17-2017, 11:29 AM
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Originally Posted by obscene View Post
what happens when it's back to 80F tomorrow morning?
That's why I want the colortune, will adjust a little rich around 70f. I really think I'm still far off and not sure you can read plugs properly with unleaded.
Old 07-17-2017, 03:12 PM
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I use Colortunes during idle adjustments on my carb teat engine but I have become somewhat more reliant in achieving "Lean Best" by adjusting mixture screws in using 1/4 turn adjustments and waiting to see if engine stumbles. If it does not stumble I then give another 1/4 turn in. Once the engine stumbles I then open the mixture screw 1/2 turn & repeat the procedure for the other five cylinders. Typically the engine idle speed will increase which throws everything off so this procedure will require repeating.

I then blip the throttles to see how the engine takes the gas from idle. If it is a little slow to respond then another 1/4 turn open will probably set you right. Obviously the air flow must be balanced for all cylinders before performing the Lean Best procedure.

Colortunes are a great diagnostic tool to help isolate what is wrong with a cylinder not firing/running well but to shuffle from cylinder to cylinder is a pain. I do recommend using it & observe how the mixture responds during the Lean Best procedure I outlined above; very educational.
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Old 07-17-2017, 07:02 PM
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Paul, thanks for your help. I had never had much success with lean best since I was not able to notice an idle speed change. Maybe my starting point was off, where do you usually start on a rebuilt carb, three turns out? Or do you open until it stumbles and then close until it stumbles and open 1/2 turn.

First the 67S and now the business, you will surely be missed!
Old 07-18-2017, 04:47 AM
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Like you, I struggled with the 'lean best' method while trying to adjust the Zeniths in my 1970 911T. Frustrated, I searched this forum and found Paul Abbott's posts very informative and well written. I studied the information on his website and ordered a Colortune. This spring, after disassembling and cleaning the carbs over the winter, I tuned them using the Colortune and I'm genuinely surprised by how well my engine now runs! No more backfiring, popping or hesitation and much improved fuel economy. The car is now a real blast to drive and I'm thoroughly enjoying it.

I can send you information on where I purchased the Colortune if you like - I don't think Pelican sells it. Ordering from Canada was not expensive and delivery time was good.

I don't understand your comment about Paul's business - is he closing it? If so, I sure hope he continues to contribute to this forum! Much appreciation for his knowledge and generosity in sharing it.
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Old 07-18-2017, 05:49 AM
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I don't understand your comment about Paul's business - is he closing it? If so, I sure hope he continues to contribute to this forum! Much appreciation for his knowledge and generosity in sharing it.
Thread in Off Topic Discussions board.
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Old 07-18-2017, 06:23 AM
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67S didn't sell but will make a reappearance soon; sporting a slight make-over!

Seriously thinking about selling business but I won't quit supporting the carb community.
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Old 07-18-2017, 07:24 AM
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you have me considering a colortune even though I have CIS and an LM2.

not to go OT but my 930 likes to idle rich, like in the 10's. would like to see what a colortune shows.
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ [__] RUNNING: [__] NOT RUNNING:
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[] RUNNING:[_] NOT RUNNING:__2000 MER E320 WAGON [_] WRECKED:[]RUNNING:
Old 07-18-2017, 08:42 AM
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Quote:
Originally Posted by Norm01 View Post
I had never had much success with lean best since I was not able to notice an idle speed change. Maybe my starting point was off, where do you usually start on a rebuilt carb, three turns out? Or do you open until it stumbles and then close until it stumbles and open 1/2 turn.
Obviously I'll not suggest to give a visit to Paul's site ...
I'also run with Zeniths and tuning them it's just a matter of patience and love.

I suggest to start with 3 turns out and step by step go to 1/4 in ... wait 5 seconds before going in another 1/4 and in the meanwhile listen to the engine sound.

When tuned mine I started with 3 turns out... I also had a digital RPM counter hooked to the distributor... near the lean best I read an RPM drop of 3-5 rpm.

There I noticed that going another 1/4 in produced a really noticeable drop of 20-30 RPMs.... (really noticeable!!!)

there you should go 1/2 out to recover to the "lean best" staus and then go to the next cylinder.

when you tune all the six cylinders reset the idle to 1000-1100 and start over.

ohhh.... it took me about 5 hours of patience ...

Needless to say that your carb need to be in good order and that air has to be balanced first!!
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Old 07-18-2017, 10:56 AM
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Yeah, patience & learning to "listen" to your engine. You gotta wait around 5 seconds after a 1/4 turn "in" adjustment (a leaning adjustment) to allow the system to stabilize. Fizeus has it right!

One note about Zeniths: The thread pitch for the mixture screws is VERY fine compared to that of Weber mixture screws so perhaps a 1/2 turn would be a better adjustment for those.
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Old 07-18-2017, 06:45 PM
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Quote:
Originally Posted by 1QuickS View Post
Yeah, patience & learning to "listen" to your engine. You gotta wait around 5 seconds after a 1/4 turn "in" adjustment (a leaning adjustment) to allow the system to stabilize. Fizeus has it right!

One note about Zeniths: The thread pitch for the mixture screws is VERY fine compared to that of Weber mixture screws so perhaps a 1/2 turn would be a better adjustment for those.
Thanks for the tip on the Zeniths! I need to learn how to use the 'Lean Best' method because using the Colortune is a bit of a pain.

Speaking of pain, have you ever received a shock through the mechanic's mirror? It happened to me a couple of times and I'm worried it could send into cardiac arrest!
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Old 07-19-2017, 05:35 AM
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Just my $0.02. Here is my change to the above (excellent) procedure.

I use the hand throttle and raise the rpm to about 2500. This puts the engine just below the idle-main transition point. It makes for much faster adjustment time due to fast response of the idle mixture screw changes. It also allows you to tune for Lean best at the transition so that you don't have to go back and tune out any flat spots during transition.

My car gets 1/8 turn in/out for Spring and Fall to account for average temperature change. And yes, I have been known to stop in the middle of a drive and adjust the mixture due to diurnal temperature changes during the day.
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Old 07-19-2017, 05:53 AM
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Agree with jpnovak about the 2500 RPM mixture screw tuning. Very good recommendation! With one drawback: since throttles are opened up quite a bit beyond idle, the air flow is less affected by variations in throttle valve fitment in the throttle bores. So, when at idle where the throttles are almost closed, you will see air flow variations from bore to bore which will affect mixtures. The result may cause idle & off idle performance to be a little rough. Additionally, depending upon how linear your progression circuit mixture strength is matched to your engine's needs, you may end up with a somewhat leaner/richer mixture at idle.

I'd set idle air corrections at idle speed & perform Lean Best at 2500 RPM (if you do not have a hand throttle then you can construct an adjustable link to temporarily replace the link from the bell crank at cylinder #3 to the throttle cross bar using a turnbuckle from Home Depot & all thread rods with some ingenuity) and then check idle performance again.
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Old 07-19-2017, 06:46 AM
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Absolutely Paul! I don't adjust the mixture until all the throats are balanced at idle speed. I assumed the OP would have this done as part of the process.

Also, the linkage needs to be balanced to adjust Lean Best at 2500. It is an iterative process going back and forth between the two speeds to check and verify function. totally worth the effort.
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Old 07-19-2017, 08:37 AM
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Quote:
Originally Posted by 1QuickS View Post
67S didn't sell but will make a reappearance soon; sporting a slight make-over!

Seriously thinking about selling business but I won't quit supporting the carb community.
Just read in Automobile magazine an interview with the CEO of Porsche North America where he says that he wants to give himself a 67S for his upcoming 50th. Maybe a potential bidder for your 67S?!
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Old 07-20-2017, 03:56 PM
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just ordered a color tune. found one for $56.
I am really curious what it will show on the 930. I am running about 11 at idle, extremely rich, but it likes it there. plus if I lean it out the cruise goes in the 16's.
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ [__] RUNNING: [__] NOT RUNNING:
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[] RUNNING:[_] NOT RUNNING:__2000 MER E320 WAGON [_] WRECKED:[]RUNNING:
Old 07-21-2017, 04:10 AM
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