How To Tune And Balance Your Carburetors
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- Опубликовано: 24 ноя 2021
- Tune and Balance your Carburetor
Can I teach you how to tune and balance your carburetor in just over 40 minutes?
No Way!
But I can set you up for success. Please take the time to sit through the engine running parts, they may be long, but you need to learn how to listen for engine drop and then lift back up. We show you with a timing light as well, but the light is just behind the actual, so your adjustments might swing. I use the sound and feel from years of practice.
Your engine and timing must be in good working order. There is no point tuning your carburetors if you have base problems. Carbs come last.
Using a synchro meter is another big part of the job. Do not use a Uni-sync or other device that restricts airflow. Ditch that type of tool, you are not doing yourself any favors.
The first balance is within the carburetor, getting all throats pulling the same airflow.
This carburetor has a split throttle, so adjustments can be made to match all three throats.
Next, you can work on the mixture screws. We are assuming you have watched our other series on rebuilding carburetors. If you have not rebuilt your carbs, it is still relevant to set up the bench measurements. Mixture screws 2 turns out, pump volume .5 of a CC, throttle plates just covering progression ports, and your float heights are set correctly.
Check out this video for these bench settings.
• Assembling a Weber 40 ...
It takes a few of the videos to get all the information, so check out the series here
• Carburetor
You can drop the idle as you tune and balance. Ideally, it should be 850 to 900 RPM. More than this and you start to engage your progression ports.
Balance side to side.
Check acceleration and deceleration, and return to idle. We adjust the pump volume and recheck the acceleration until it is better. You can experiment in each direction and see if you have made an improvement or not!
Once you have set up your carburetors, it is time to connect them. Put on the crossbar and linkages, making sure to not be pulling on the throttles. Check the balance at idle and off idle. Balance and recheck at idle.
Drive the car and recheck the idle mixtures.
We are not sponsored by anyone, if we provide any links, these are the tools or products we use. If you click on a link and purchase, we will get a small amount of change, at no cost to you.
Synchrometer, amzn.to/3HKp20c
Timing light, amzn.to/3r62i53
Grease, amzn.to/3HJsJmG
Allen key set, amzn.to/3DKmaOA
Good luck, and happy tuning. Always Porsche responsibly.
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Hands down, the most comprehensive brief tutorial on the Weber carburetor I have ever seen. I have learned so much from you and I so appreciate how you break the 911 down into elemental bits. I am no longer afraid of the 911 engine!!! Thank you!
Glad that we can help you understand your car better
Kurt
Kurt Seasons Greetings
Your carburetor series are awesome! Outstanding video work and explanation on this process.
Your Channel will become the most important tool in anyones tool box that has an early 911
Keep up the great work and thank you for sharing this valuable information!
Cheers!
Thanks Mike, we hope this can help anyone with a carburetor and the 911 guys too. Best for the season to you. Kurt
Well now I have to start over tuning my carbs! Great video as always! So much great information! Happy holidays Kurt and Sarah!
Thank you! You too!
Kurt
Wonderful video. Greatly appreciate how you provide context to vocabulary as you speak explaining the affects of symptoms experienced while tuning or tinkering, one of your many strong points as a teacher/mentor.
Thanks Fancypants,
Glad you enjoyed it and found it useful
Kurt
Wow, thanks for the very clear and easy to understand video. This is the best air cooled 911 channel on RUclips.
Thanks glad that you like it
Kurt
Well done! All of your videos are so incredibly helpful as I go through my 1970 911 restoration project. Keep them coming!!
Thanks Andy
We will keep them coming
That's a lot of experience boiled down to 40 minutes. Very well done. Clear and easy to follow.
Glad you enjoyed it!
Kurt
Enjoyed the video
Well explained.
Camera work, spot on!
I now have the courage to tackle this procedure. Happy Holidays!
John,
Thank you for your kind comments, and I'm sure that you should be able to tackle this operation on your car.
Kurt
Thank you. Best tutorial I’ve found so that I can actually do this myself. Appreciate the (appropriate) level of detail!
Glad it helped! S
Great tutorial with tips on small adjustments or technical issues that might otherwise get missed!
Glad you enjoyed it!
Kurt
Great video, thanks . Very informative and helpful.
Glad you enjoyed it!
Kurt
Thank you so much for your detailed break down. Having spent a few days getting familiar with the Weber 40 IT triple down draught carbs on my Alpine A310 V6 your video is clearly showing answers to my queries. Subscribed. Thank you so much.
Glad I could help!
Kurt
This is such a helpful video thank you! I was told that both the air bypass AND idle mixture should have a bench setting of two turns out. After watching this video, looks like you keep the air bypass all the way in, then make slight adjustments. Wow, I have been chasing my tail for weeks until I studied this video. I am tuning my 1970 911T with Weber carbs (just like this one).
Yes unfortunately you got some bad information on the air bypass screws. If all the air bypass screws are open or "Bench Set" at two turns out then it will cause a lot of problems. It will change the progression port timing by causing the throttle plates to sit lower in the bore to get an idle speed. This will result in some weird lean spots at part throttle applications. It will also cause a lot of back firing on deceleration.
Kurt
@@klassikats Yep, that is what I have been fighting for a few weeks. I have my snap on timing light for the digital tach and following every step you took . My 911T is now tuned and not backfiring or having weird tune ability issues. Paid you $$ for the help.
Thanks I appreciate the support
Awesome content. Just love to see your fine videos. Thanks for it.
Thank you Michael
Kurt
Excellent!
Glad you liked it!
Thank you, i just have the same porsche with same carbs to adjust , this is very helpfull!
Glad it helped
Kurt
Thanks!
Thanks I appreciate the support.
Kurt
Great job on the textbook explanation.
The problem I'm experiencing is hard hot start and a loaded up feeling after flooring it to get it to start. This will set up no idle and no power until up in the midrange.
This leads to embarrassing traffic light stops and not wanting to do errands.
Accelerator pumps seem ok.
Sticky float or leaky seat could explain flooding but why so long to clean up?
It can go on for minutes.
Runs great till I stop.
Jeff,
Certainly sounds like it is flooding. This can be caused by a number of things. Bad or sticking floats, worn out or contaminated needle and seat valves, or excessive fuel pressure. The reason that it can a long time to clean up is that you have most likely fouled the plugs and excessive fuel is also probably still flowing into the engine. I would confirm that the engine is being flooded then resolve the issue causing it.
Thanks and good luck
Kurt
Sar great teach
Thanks
Kurt
Thanks for sharing. All tuning here is applicable to my 46mm PMO's that i'm currently trying to get to run a bit leaner at idle and not lean spike at 2-3k transition. Just about to reset float heights as all seem a bit different.
Emulsion tube selection will greatly effect the 2000-3000 transition between the idle jet circuit and the main circuit. Most carbureted engines like it a little rich at idle. Not a big deal.
@@klassikats I'm on F16's and maybe over thinking it now that I have a wide band. ruclips.net/video/rSC-eLJ4Kqs/видео.html
Wonderful video and excellent comments. Please add hints/suggestions specific to Solex 911 40PI carbs. Thank you!
So we have video on rebuilding the Solex 40PI carburetors but not one on tuning. You can see it here ruclips.net/video/5mv_2g8L3-s/видео.html However, Tunning on these are completely different than the Weber triples. The principle is the same but the process is very different in that you are adjusting linkages to achieve air flow numbers versus bypass screws.
Kurt
Hello, love your videos. Very articulate in your explanations. Anyway, I was hoping you could offer me some insight. I have a 2.7 that has been converted to a 2.9 and uses 964 cams (from previous owner). Engine was running ok, maybe a little hard to start, but I took it apart for a upper end refresh/valve job. Set the cams back to 964 valve lift (per your other videos) and rebuilt the carbs (40IDA) mostly just to freshen up the seals and ensure they were clean. Initially the carb settings were no where near your settings, Mixture screws were around 7 turns out, air bypass screws were 4+ turns out, idle screws 2-3 turns in, it was all over the place. Following your guide I set the carbs up as you instructed but it won't start, best I can get is a sputter. If I hold the throttle open and crank it long enough sometimes it will start but bog down and die. Carbs remain full of fuel. I never touched the ignition aside from plug wires which I have double checked routing. Truly, I'm at a bit of a loss and hoping you can advise.
it sounds like it is not getting enough fuel to run and maybe to much fuel while cranking. If everything is set right you should be able to give the carburetors two or three pumps and the engine should fire.
I would start from scratch, leak down the cylinders make sure you have a good seal. Pull the plugs and clean off all the fuel from them. Confirm ignition is fully functionally and the points are set correctly , CDI box is humming with ignition on. lastly, fuel pump runs with ignition on, fuel in the bowls and not spilling over flooding the engine. accelerator pumps delivering fuel when you pump the gas.
If all of the above are correct the engine should start and run.
After doing the above and you still cant get it to run you can book a time with me to look at it with via a video chat. you can book here www.klassikats.com/consultation-services/
Thanks Kurt
Love the video, have you ever used the "Colortune" spark plugs, where you can see and tune the colour of the combustion?
Varmays,
As a professional mechanic, I would not ever use a colortune plug. I have other tools available to me like a 5 gas analyzer that if I needed to will give me instant feedback as to what is really happening inside the cylinders. I must admit that it is more of a gimmick to me than an actual tool. However, I will say that it takes a lot of practice working with carburetors to really become proficient at tuning and setting fuel mixtures. The other points against it especially on a 911 engine is that you would need 6 of the colortune plugs as each cylinder is fed by its own carburetor barrel. Also, it is best practice to tune the engine using the spark plugs that it will be running with. And lastly depending on camshafts and compression fuel settings and combustion at idle may not always be ideal especially in a high revving performance motor.
Thanks Kurt
@@klassikats Thank you Kurt for your comprehensive answer.
As an amateur mechanic 😉, I use the colortune plug because I find it very difficult to hear correctly when the idle fuel mixture is in its correct position.
I am convinced that it is not the best way but it is a way to get my engine to run smoothly.
@@varmays Yes, it does take some experience to correctly hear what is going on when tuning. I tell people that when I started in the industry I thought I was pretty good at tuning carbs, now 33 years later I realize that I sucked for the first few years. The other thing to keep in mind is that the engine is giving you a lot of feedback signals and not just the sound that it makes. One last thing to keep in mind the longer the engine idles the harder it will be to set the tune. I generally will set fuel mixtures in about 2 - 3 minutes. If the engine is left idling while making changes for more than 10 minutes you need to drive the car to clear the plugs then start again
@@klassikats Limiting the time for tuning was a tip I hadn't read or heard anywhere, so I'll probably have to watch the video about 10 times more to understand everything.
Thanks for all your work!
Hi Kurt, love this video. Is the PMO tuning basically the same as the Weber? Also, I’m setting my cross bar and can’t get the tension out of it. As soon as I tighten the mounting plates it gets fairly stiff and no adjustment on the LH nut can get it out. Maybe the plates are bent? I’m thinking of using some washers to try and space them out a little. What do you think?
Rob,
The set up on PMO carburetors is the same as Weber carbs. On the cross bars take a look at the lock nuts for the adjusting ball and make sure that they are slim locking nuts. If you have regular size nuts installed it is possible that the pivot ball adjustment will be to tight.
Kurt
IMPORTANT: This is a thorough tutorial on the basics for setting up your carbs on a 911 but there is one very important instruction that is missing (unless I accidentally skipped over it): When doing the initial airflow balancing you may be tempted to turn the idle stop screws in to get the car to idle. This is ok, but NEVER try to balance the carbs with those screws turned in more than 3/4 to 1 turn after the screw has initially started to activate the butterflies. The reason is that you run the risk of exposing the first progression hole in the carb throat and you will be fighting an overly rich idle. You will get high airflow readings (way higher than the max of 5.5) because of all the extra air flowing by because the butterflies are cracked open. Also, if you have the progression hole exposed, you will notice that the mixture screws won't have much effect. If you already have your carbs off, you can test to see the maximum turns of the idle stop screw before exposing the progression holes. Make a note of this and never go past it even with your final idle setting. On my carbs is was around 1.25 turns. So I preset mine at 1 turn before tuning the carbs and never turned them in more. Thanks again to Kurt for these fine videos. They are really helpful. If you ever decide to redo the instruction video a nice enhancement would be a pic in pic of the RPM.
Richard,
So yes I cover this in our rebuilding and bench settings videos. However, you have to be careful putting all carburetors into the same bucket. For example, The weber IDTP carburetors have a small progression port that is designed to open at all times. Even if you completely close the throttle it will still be exposed. This type of carburetor use the mixture screw as a volume control as opposed to an on off switch in earlier models.
Your comment is basically correct, to much open throttle will cause no end of issues.
Kurt
This excellent video inspired me to re-tune my carbs and now my '70 911T (with Zenith carbs) runs stronger, idles better and its plugs look much better, less sooty. Unfortunately, I now get backfiring going downhill with my foot off the gas. From what I've found looking on the web, this is due to a lean condition because the carbs are supplying fuel through the idle circuit only, which is not enough to support combustion. The unburned fuel then ignites in the muffler, where there is enough heat and oxygen. My Zeniths had the auxiliary enrichment system but I took it off when I rebuilt the carbs a few years ago. Is this backfiring something I should just accept or is there a way to minimize it?
Michel,
There are a few things that can influence backfiring on deceleration. One of the biggest issues is exhaust leaks. When you have an exhaust leak not only do exhaust gasses leak but oxygen is also able to be drawn in as the exhaust pulse passes the leak. The presence of oxygen in the exhaust enables fuel to ignite and this results in backfiring.
The system you removed was also specifically designed to eliminate backfiring on deceleration. Removing from the carburetors did not gain you anything in performance or reliability, I would suggest re-installing it and correctly setting it up.
Lastly, ignition and fuel settings will also play a part in backfiring. Make sure that fuel mixtures are not overly lean at idle and that your ignition timing and distributor are working as they should. Make sure that you have the correct distributor for your engine as well.
Hope that helps
Kurt
@@klassikats Thank you for your reply, Kurt. Yes, it helps and it confirms what I suspected - that I have to re-install the auxiliary enrichment system. I'm quite confident that the exhaust and ignition systems are in good working order. The fact that an enrichment system was part of the carburator system indicates that backfiring is expected on deceleration when the Zeniths are properly tuned.
Kurt, thank you for sharing your wealth of knowledge and experience with us! I have been scouring your IDA videos because I have a 66 911 with 40 IDA 3C’s that will drip fuel out the progression holes of #4 only, and only after shutoff. Floats are 12-12.5 mm, 3-3.5 psi fuel pressure, new floats, clear passages as far as I know, but without removing any plugs. Any thoughts on how this could occur?
I would look at the idle air bleed and make sure it is clear. If not it will siphon fuel through the progression port.
Kurt
@@klassikats thanks for your help! Will check it out.
@@klassikats Kinda weird. The idle vent is clear and with the jet and holder out, it doesn’t change the volume of the leak, but when I put fingers over the vent and jet holes simultaneously, the leak accelerates. Then when I take a finger off, there’s a rush of fuel, and then it levels off to a drip again. I’m beginning to think I have an internal flaw in the casting, because I don’t know of a way for fuel to travel from the bowl to the progression port chamber without going through the idle jet. It definitely comes down through the top channel and into the chamber. I can put a 1/16” drill bit into the idle jet hole and it will go clear to the back of the passage under the plug, but it doesn’t change the leak volume. Otherwise it just leaks down to a certain point and quits. Still scratching my head. I’d appreciate it if you could share any more ideas.
@@klassikatsI haven’t been able to figure out how fuel can drip out of the idle circuit on the #5 cylinder only, when the float level is at or below below normal. It’s not going through the idle jet, the idle air bleed is clear, and so is the emulsion tube and main air jet. There has to be some connection between the main well and the idle circuit other than through the idle jet. I’d like to pay your consultation fee, or even send it/them to you, if you think you can fix it. I appreciate you answering initially, and I know your time is valuable, but please let me know if this is something you’d like to tackle and I’ll schedule accordingly. Thanks Kurt!
@@klassikatsI realize now that I fat fingered the 4 originally, but it’s cylinder 5, the middle barrel on the passenger side. Apologies 😊
After watching the intro, I didnt hear anything about throttle linkage. Does that also have to be perfectly setup before balancing the carbs? Or can the carbs be adjusted independent of the Throttle linkage??
I am so confused, it doesn't help that I am not (yet) very knowledgeable about these things. i am still going to watch the full video, maybe I'll learn something.
My car, mazda miata with bolt-on ITB's (carbs) is idling bit high , throwing engine codes and has a RPM hang at 2,000RPM. My mechanic did NOT balance the carbs....and he is not willing to help me. I am learning so I can try to attempt this myself...
MrM Setting up the throttle linkage is done after the carburetors have been balanced. Your car was most likely never designed to have carburetors on that engine. It would have originally been set up with fuel injection. There could be multiple issues with your set up. Also it is not likely that the engine light will ever turn off as the ECM is never going to see what it is looking for with carburetors on that engine.
good luck with it
Kurt
@@klassikats thank you for the reply. Believe it or not, that helps me a lot! Now I know I should balance the carburators first and then i'll worry about the linkage. 1 of the engine codes i'm having is a "MAF (Mass Air flow/volume) code" and I think it might be because I haven't balanced them. The other code i'm getting is "system too rich bank 1" so I guess that will be solved by getting the car tuned by professional tuner.
Thanks!