Educate me on AFR gauge options for 3.0 with Weber's

[Derek77]

Hey guys,

Please forgive me but I'm new to tuning and I want do it correctly the best way I can.

I have a 3.0 engine with Weber Ida's and MSD 6A. I recently replaced all the gaskets on my carbs and got them running with no popping or other issues I can see. My concern is I can't seem to identify best lean idle mixture by playing with the mixture screws. I've tried turning them in/out a lot and I can't really notice much difference. My engine starts, idles, and runs well. No popping, no sneezing, no flat spots but it would just be dumb luck if it is all set properly at this point. The only thing I notice right now is upon cold start the engine idles really low (500-600rpm). Once she warms up the idle is steady at 1,000rpm. Prior to me messing with the carbs it would idle around 1,000 on start but then would go to 1,200 once warm which was annoying.

My idea is to get a colortune to check idle mixtures. I have read all the negatives and positives and I can deal with the negatives.

Secondly I would like to have some sort of AFR gauge that allows me to see what is happening and make sure I'm not damaging my engine. I just want something basic and inexpensive. I've looked at the AEM gauge 30-4110 and also the 30-4900 but I don't even know what I need at this point. Can I reliably tune this car with just the 4110 or should I get a 4900? Do I need data logging or can I have a passenger watch it while I drive?

Any suggestions are appreciated.

Thank you,

Derek

[lvporschepilot]

Hey Derek, you have no choice with carburetors re cold running. Always tune when fully warmed up. From a Lamborghini Muira to 911, the way I tune idle with carbs with individual throats is to first sync them so they are all drawing the same amount of air, then turn idle screws in until that cylinder dies, then screw out 1/2-3/4 turn from where the cylinder died. Progression and WOT jetting can of course be altered using the information gathered from a wideband such as what you mentioned or an Innovate LM-1 or the like.

[T77911S]

try a color tune that goes into the spark plug hole.
I have one although I have CIS, pretty cool tool.
I would tune as above and then go through with the color tune once close..

if you are not seeing a change then you could have dirt in there.
one other thing that may cause it is if the throttle stop screws are not set correctly. these are a mechanical setting, not really an idle adjustment. you may have these adjusted in too far. back them out half a turn and reset idle with air bypass screws and see if the mixture screw has an effect.

idle mixture is not going to hurt your engine. your idle circuit is not being used at WOT.
you can check plugs for mixture setting. \
make sure your ignition is in top working condition along with timing set before adjusting carbs

[dicklague]

I have used an AFR instrument in my '73 911 with MFI for years. Make sure what you get allows you to gather RPM, MAP, and AFR readings over time. That means one with memory and data you download.

The best instrument out there is the Daytona-Sensors WEGO IV
http://ig3tech.com/wego-iv-afr-instrument-by-daytona-sensors/

[Trackrash]

An AEM A-F gauge works well. I have the 30-4110, not sure why you would need data logging, unless you are racing. A look at the plugs can tell you how well your cylinders are balanced at idle as a double check. FWIW, your idle adjustment will be a compromise, no matter what, due to the changes in temperature. The AEMs value is in knowing what your AF is in driving conditions, especially WOT.

[Norm01]

Derek, I’ve done the colortune and AFR. Still have both however if you can’t achieve lean best these won’t help you. Once you’ve air flow balanced your carbs lean best is very noticeable. Remember to wait about 5 seconds or so for the change in idle. Your carbs are propably due for a good overhaul.

[Derek77]

Thanks guys for all of your replies. I have ordered a colortune and will start with that and see how it goes. I will examine the AFR options once I play with the colortune.

Originally Posted by Norm01

Derek, I’ve done the colortune and AFR. Still have both however if you can’t achieve lean best these won’t help you. Once you’ve air flow balanced your carbs lean best is very noticeable. Remember to wait about 5 seconds or so for the change in idle. Your carbs are propably due for a good overhaul.

Thanks Norm. I set my carbs up with the mixture screws 1 3/4 turns out and the air bypass screws closed. Maybe I'm misunderstanding how to do the procedure properly. I'm turning the mixture screws with the air bypass screws closed. Once I think the mixture screws are set I'm using the air bypass screws to balance the vacuum on each barrel. The problem is I'm having a difficult time noticing a difference when I turn the mixture screws. I could be getting impatient and turning the mixture screws too much at a time. I am waiting 5-10 seconds after turning them to look & listen for changes. I just replaced all the gaskets on my carbs and tested the accelerator pump output. Paul Abbott was kind enough to exchange a few emails with me. He seems to think my carbs sounded okay based on my description of them. He did say I might benefit from his basic overhaul of the throttle shafts which I don't doubt at all. I'm struggling with spending a lot of money on my Weber's. My car is not at all an original so if I was going to spend some money it would probably make more sense to sell my Weber's and purchase new PMO's. The cost after selling the Weber's would probably be similar. Any thoughts?

Derek

[jpnovak]

Does the car stumble when you turn in the screws? It should start to stumble and mis fire if you turn them in far enough.

Are you sure that your idle passages and jets are clean?

I usually do the "lean best" at about 2500-2800 rpm. The transition is easier to find and takes less time. This also allows you to fine tune the idle to main transition. I don't worry about how lean it idles as long as it pulls smoothly through the transition and rest of the rpm range.

Also, if you are overall too rich on all cylinders you may have a hard time detecting lean best on a single cylinder. 1.75 turns should put you very close as long as you are jetted properly.

Are your idle mixture adjustment screws matched to the car body. Meaning, the fine adjustment needle versus the "blunt" needle? A mismatch between the two will make it hard to detect the transition.

Are you sure you have float levels set correctly and no fuel is leaking?

[Norm01]

Derek, have you spoke to Paul about your settings vs your engine. Main jet, idle jet, venturis and so on. Paul will be able to tell you if you are in the ballpark. I have been learning Weber’s for the past five years, just starting to figure it out. Oh yeah, the colortune. Here’s the deal, engine needs to be warm, pull hot plug, install colortune (not easy in that deep cavity). Start engine, can’t see anything inside that cavity, get seriously zapped. Turn off engine, remove colortune, throw across yard.

[Porsche 2]

I had similar issues re turning idle mixture screws with little change. I discovered that the mixture screws come in different thread designs. Some are threaded all the way from the tapered end to the screw head. In my case the threads start about 1/4" from the head, and while the O ring "cup" washers slid over the threads they did not slide over the unthreaded part of the screw preventing the tapered needle part of the screw from seating closed. So when I thought the screws were fully inserted, they were not. I drilled the washers out just enough so the washers would slide over the non threaded part of the screw, which allowed the screws to be fully seated. This allowed proper function of these idle adjusting screws. Who would have thought?

[larrym]

yrs back i used a older narrow band dual sensor setup on my weber engines - just install a switch so you can trigger either side from the dash

- worked just fine to get jetting in the ballpark for street driving

color-tune is a PITA on a 911 engine - fine on MGB -

on either case - no way you can see what's going on where you want to know it - on the road!

now i run an AEM on my 3.2

p.s. - there are plenty of threads here on jetting webers - some with likely the exact info you need for your setup - just google it

[Derek77]

Originally Posted by jpnovak

Does the car stumble when you turn in the screws? It should start to stumble and mis fire if you turn them in far enough.

Are you sure that your idle passages and jets are clean?

I usually do the "lean best" at about 2500-2800 rpm. The transition is easier to find and takes less time. This also allows you to fine tune the idle to main transition. I don't worry about how lean it idles as long as it pulls smoothly through the transition and rest of the rpm range.

Also, if you are overall too rich on all cylinders you may have a hard time detecting lean best on a single cylinder. 1.75 turns should put you very close as long as you are jetted properly.

Are your idle mixture adjustment screws matched to the car body. Meaning, the fine adjustment needle versus the "blunt" needle? A mismatch between the two will make it hard to detect the transition.

Are you sure you have float levels set correctly and no fuel is leaking?

Thanks Jamie, I didn’t get it to stumble so I’m going to take the springs off the mixture screws and mark them while closed to confirm I have them fully closed. One of my mixture screws was different than the others so I replaced it.

I check idle jets frequently and I think passages are clear. I completely disassembled carbs except throttle shafts. I cleaned every passage multiple times with carb cleaner and also a parts washer at an aviation shop. Also blew them out with compressed air.

I spent a lot of time checking l float levels and used the pmo gauge not running and also running. I’m confident float levels are correct and no leaking.

[Derek77]

Originally Posted by Norm01

Derek, have you spoke to Paul about your settings vs your engine. Main jet, idle jet, venturis and so on. Paul will be able to tell you if you are in the ballpark. I have been learning Weber’s for the past five years, just starting to figure it out. Oh yeah, the colortune. Here’s the deal, engine needs to be warm, pull hot plug, install colortune (not easy in that deep cavity). Start engine, can’t see anything inside that cavity, get seriously zapped. Turn off engine, remove colortune, throw across yard.

Hi Norm, I haven’t but I’ll reach out to him. I don’t like bugging him and he has helped me a lot already. Yeah heard lots negative on colortune. Waiting for a day I feel real calm.

[Derek77]

Originally Posted by Porsche 2

I had similar issues re turning idle mixture screws with little change. I discovered that the mixture screws come in different thread designs. Some are threaded all the way from the tapered end to the screw head. In my case the threads start about 1/4" from the head, and while the O ring "cup" washers slid over the threads they did not slide over the unthreaded part of the screw preventing the tapered needle part of the screw from seating closed. So when I thought the screws were fully inserted, they were not. I drilled the washers out just enough so the washers would slide over the non threaded part of the screw, which allowed the screws to be fully seated. This allowed proper function of these idle adjusting screws. Who would have thought?

Very interesting, I’ll check this out. All but one of my mixture screws look like one in first picture. Second picture one I replaced with one in third picture.

I’ve been working on my other issue which is taking slack out of throttle linkage. Yesterday I replaced the three bushings in the tunnel. They were all totally gone.

I have been driving the car and it seems to run really well. No noticeable flat spots or other issues. I’ll get there but I have limited time to work on this. I did notice my mpg dropped from 18 to 14 with changes I made. Not perfect comparison I’m sure. What kind of mpg are you guys getting? I realize driving style could vary it a lot but curious.


Thanks guys!

[rennzeit]

Read Paul Abbott’s procedure and notice his section on tuning 40ida on large displacement (3.0 and up) Performance Oriented

“Those tuning IDTP Webers will be working with mixture screws having a tip with a needle like end followed with a short cylindrical body before the threads start. All other mixture screws for the Webers have a continuously tapered tip. The non-IDTP mixture screws are far easier to use since fuel flow incrementally changes with screw adjustment but the IDTP screws provide little finesse in idle mixture adjustment.”