Weber DCOE Tuning

[Origin7]

For those of you tuning and learning about Weber DCOE carburetors, you may be in the same situation I was, where finding good information and knowledgeable advice has become increasingly difficult. I’m starting this thread to share information that others may find useful, and I encourage everyone to add their own experiences and insights.

 

With that said, I want to recognize the work that Keith Franck has been doing. He runs a forum focused on Weber carburetor tuning and also manufactures custom Weber components. His forum can be a little difficult to find and isn't the most intuitive to navigate, so with Keith's permission, I've uploaded several of the documents he's written. His white paper, in particular, has been immensely helpful. Keith mentioned that it is due for an update, but even so, I found the information to be invaluable.

 

https://vintagetechnologygarage.groups.io/g/sidedraft

 

One thing I would highly recommend is installing a wideband O₂ sensor. I think it's almost essential if you're new to tuning carburetors and don't have much experience interpreting plug color, engine sound, exhaust smell, and the other subjective methods that experienced tuners often rely on. I installed an AEM X-Series, and it's been an excellent tool. It was easy to install, simple to set up, and completely removed the guesswork.

 

Another key lesson I learned from Keith was to measure the fuel level with the carburetors installed on the car rather than relying solely on setting the float height while they're disassembled. Keith used to sell a tool for this, but he no longer offers it. I ended up using the depth rod on the back of a vernier caliper along with a flashlight. If you watch the fuel surface closely, you can see exactly when the meniscus is disturbed, making it surprisingly easy to get an accurate measurement. Going through this process revealed that my fuel levels were nowhere near the recommended 25 mm target. Correcting them nearly eliminated a lean bog that I had been chasing by richening the idle circuit.

 

I still have some tuning left to do and will continue to post updates. Keith also designs and manufactures his own emulsion tubes and jets, which I may try next. Feedback from the community has been very positive. If anyone here has used them, I'd be interested in hearing about your experience.

 

 

Weber_DCOE_Tuning_White_Paper.pdf Fuel_Level_Setting_Instructions.pdf

[JohnCh]

Thanks for starting this and getting permission from Keith to post the docs. I'll add those to the Library later this week. I joined Keith's forum a couple of months ago and have been casually monitoring the email discussions, but I've been waiting to really dig into this topic until the new engine is finally installed in the Elan. I agree about adding a WBO2 sensor and have already wired in an AEM X-series and a Nodiz 3D ignition module from Motorsport Electronics. The data logging function will allow me to log rpm, throttle position, and AFR (actually the AEM voltage output, which I then need to convert into AFR). I'm hoping this should make things a little easier since it removes the guesswork of where and when it's rich or lean, and by how much.  

[Origin7]

1 hour ago, JohnCh said:

Thanks for starting this and getting permission from Keith to post the docs. I'll add those to the Library later this week. I joined Keith's forum a couple of months ago and have been casually monitoring the email discussions, but I've been waiting to really dig into this topic until the new engine is finally installed in the Elan. I agree about adding a WBO2 sensor and have already wired in an AEM X-series and a Nodiz 3D ignition module from Motorsport Electronics. The data logging function will allow me to log rpm, throttle position, and AFR (actually the AEM voltage output, which I then need to convert into AFR). I'm hoping this should make things a little easier since it removes the guesswork of where and when it's rich or lean, and by how much.  

 

My pleasure! I've attached the Weber manual as well if you'd like to upload it to docs. 

 

Keith's forum gets really technical, which I like. But I need to be in the right mindset to absorb everything.  

 

Data logging would be great. I am interested in seeing how you do this. I have a bluetooth 123 Ignition, but I am not sure how to pull that data and combine it with the AEM AFR data. That will be a future project.   

Weber_Repair_Document.pdf

[JohnCh]

The Nodiz is replacing a 123 Ignition in the removed Stromberg engine. Unfortunately, that doesn't do logging, so you would need something dedicated. The data logging on the Nodiz is straightforward. ME makes several ECUs for injected cars, and use the same software across the board, which includes data logging. The big difference with the Nodiz is that a relatively recent update removed the native AFR logging functionality. Previously you could input the calibration chart that correlated output voltage to specific AFR values, and it would store the latter for the data logs. Now, it just logs the voltage. Apparently, the logs are easily exported to Excel and the conversion can be done there. Sadly, I'm probably at least a month away from trying that out.

[Origin7]

On 7/6/2026 at 12:42 PM, JohnCh said:

The Nodiz is replacing a 123 Ignition in the removed Stromberg engine. Unfortunately, that doesn't do logging, so you would need something dedicated. The data logging on the Nodiz is straightforward. ME makes several ECUs for injected cars, and use the same software across the board, which includes data logging. The big difference with the Nodiz is that a relatively recent update removed the native AFR logging functionality. Previously you could input the calibration chart that correlated output voltage to specific AFR values, and it would store the latter for the data logs. Now, it just logs the voltage. Apparently, the logs are easily exported to Excel and the conversion can be done there. Sadly, I'm probably at least a month away from trying that out.

Wow, the Nodiz setup looks nice. I wish I saw that before buying the 123. It looks like I can still grab the rpm data from the 123 ignition, but I'd need a logger or rasberry pi setup to record it.  

[JohnCh]

For what it's worth, the 123 works great and is comparatively very quick and easy to install. The 3D ignition setup requires a trigger wheel on the crank pulley, a CPS with a bracket to fit the Kent block, a plug for the removed distributor, a coil pack, a bracket to affix the coil pack, a TPS with bracket that works with DCOEs, and then wiring everything together. In theory most of those installation parts are available in the UK, but I ran into some significant issues sourcing some of them and ultimately ended up making quite a few myself and outsourcing the crank and trigger wheel to a local shop to weld and true on a lathe. Hopefully it will all work.

[IamScotticus]

I have seen this done ij a vintage film clip, and always wondered what was going on here?

Or was it on Ford Vs. Ferrari?

Can anyone explain the purpose of "beating" and "grinding" the seats?  Isn't this hammering hard on the threads? Or is this a separate plunging tool?  Are the bottoms of these seats so rough from casting or tooling they need finishing?

 

 

 

 

[wdb]

@IamScotticus if I were to pull a guess out of my nether parts I'd say the hammering was done on tools made for the job. The point of all of it would be to ensure proper seating of the parts against one another.

 

I followed Keith Franck's method of setting float height earlier this week. It did not quite completely get rid of the lean stutter at high-ish RPMs, but it is 95% better than it was. And it smoothed out the general running condition everywhere. Incredible difference. And I only had to do one carb. Prior to making changes I took measurements and I had the float level right where the manual states it should be; per Keith's method it was 3mm low. Thank you Keith!

 

As to the measurement process itself, I used a dial caliper. I set the caliper to 25 mm, dropped the protruding stem into the jet opening, and it came back dry. So I set it to 26mm, dropped it in again, and so on until it came back wet. It's a stainless steel tool and the gas was either wetting a good bit of the stem or did not wet it at all. I assume the gas wicked up the stem a bit.  To my mind the wicking didn't impact the measurement procedure because I was making 1mm changes. It either touched gas or it didn't.

[Origin7]

@wdb I'm glad to hear you had the same success that I had with Keith's process. He's a wealth of knowledge. Are you running a wide-band O2 sensor? Leaning out at high RPMs is sometimes a fuel pressure issue. I don't have this issue, but I still plan on installing a Malpassi regulator and gauge in the near future to ensure I'm getting sufficient fuel to the carbs.

 

Another important thing I've encountered tuning these carbs is how important it is to fully heat soak the engine before tuning. Warming it up to operating temp in the driveway is not enough. You really need to drive it for 15 mins or so to adequately heat soak it. I am seeing a 0.5-1:1 drop in AFR as the engine fully warms up.      

[wdb]

I have not gone the 02 sensor route. It sounds like it could be a great tool, and I may end up there at some point in the future. But I've tuned a lot of carbureted cars in my life and I have some idea of what should go where so for now I'm going to keep doing it "old school". I also know one fellow with a wideband 02 gauge and he has proclaimed it to be nearly useless because the readout jumps around so much. I don't know the specifics of his installation so there could be some issue with it I guess.