Weber 40 DCOE 151 Tuning

[Origin7]

I did quite a bit of testing over the last couple of days. I've attached my log if anyone is interested. 

 

To summarize, here are my two best setups. This is the factory setup with the exception of 125 mains and 00 pump drains. These changes seem to smooth out the transitions quite well. On the low end, I like both the 45F6 and 45F9 idle jets. For now, I am going to stick with 45F9. I like the AFR at cruise with this setup. I didn't test the F11 tubes with 00 drains, so I plan to do this in the future. For now, I'm happy with how things ended up.    

 

Test

Choke

Aux Venturi

Main

Air

Emulsion

Idle

Pump Jet

Pump Drain

Cruise AFR

Progression AFR

WOT AFR

Change Made

Result / Notes

5

32

4.5

125

165

F16

45F6

35

0

~11

~11

~11

60 → 00 drain

Very smooth, but rich

6

32

4.5

125

165

F16

45F9

35

0

~12.5

~12.5

~14

Back to 45F9

Best so far

Weber_DCOE_Tuning_81526.xlsx

[Origin7]

I know you guys love pictures (me too)....

[Origin7]

WARNING: Inspect all your genuine Weber components before installation. Their QC seems to be lacking.   

 

I received a bad banjo fitting a couple of weeks ago. The deburring was not concentric with the ID, and they removed 1/2 the sealing surface. Long story short, it would not seal and sprayed fuel all over the place. Pegasus was great and sent me a new one, which worked perfectly.   

 

Today, it was much worse. I was seeing some weird things with the F11 emulsion tubes that I tested. I had one cylinder spitting back through the carb but no other indications of a lean condition. This was only when the mains kicked in (weird). I decided to go back through things and try again. Upon inspection, it was clear there was a machining error in one tube. It looks like the bore for the main jet was not drilled deep enough. As a result, there was a bur above where the main jet seats. I was able to get inside and remove the bur, but the way it was shaped, it looks like there may have been another half-bur at one point. I am praying this didn't get into my valve train. The head was literally just done.

 

Long story short, F11s, 45F9 Idle jets, 00 drain, and 125 mains run quite well. The bad emulsion tube threw a monkey wrench in my testing, but I am glad I found this combination. 

 

[IamScotticus]

1 hour ago, Origin7 said:

I am praying this didn't get into my valve train.

is this possible?

[Origin7]

16 minutes ago, IamScotticus said:

is this possible?

No. I realized this after posting. This shouldn't be an issue...thank god. It should be too large to pass through the main jet. It could have come out one of the holes in the emulsion tube, in which case it would be in the bowl. I'll pull the cover off and have a look tomorrow.  

[Origin7]

After months of experimentation, I think it’s time to wrap up my carburetor tuning adventures. I’ve tried different emulsion tubes, idle jets, main jets, and pump drain valves across a range of driving conditions and temperatures. I’ve settled on this setup, which is close to factory with a few minor tweaks:

 

Choke: 32
Aux Venturi: 4.5
Main Jets: 125 (keeps AFR around 13:1 at WOT)
Air Correctors: 165
Emulsion Tubes: F16
Idle Jets: 45F6 (richer than the factory 45F9, which was slightly too lean, especially during progression)
Pump Jets: 35
Pump Drains: 0 (provides the full pump shot and eliminates the lean bog)

 

I’ve driven with this setup at sea level in ambient temperatures from 50°F to 95°F, and it’s proven to be a good all-around combination for my car. The lean bog and rough transitions I had with the stock setup are gone. I also pulled the plugs, and the color looked good, perhaps slightly rich, but overall I’m happy with where things have landed.

 

Hopefully, this gives others with a similar setup a good starting point and saves them some trial and error.

 

[IamScotticus]

please remind us what displacement and compression?