Euro Carbs conversion

Interesting, my assumption is that they are the same, DCNF. With all of the jetting variables available, I thought that a different spec wouldn’t be needed. You never know though.

 

I put 44s on and it makes a difference. Stock were 42s.
I think stock euro and na were the same

 

Somewhere I have a chart, by year, of the jet sizing and tubes and such, the sets are al the same, if as noted venturi is correct.
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how about that...

 

You rock!

 

The bodies and chokes are the generally same (and you could use the euro emulsion tubes, jets, etc. if you wanted to), but I'm having a vague recollection of a discussion about the progression hole patterns being different (so you might try a search using "progression holes" for those threads). The one physical difference that I can recall is that the US 1-2 carb has a "paddle" added on the throttle shaft to actuate the throttle microswitch at idle, but you could just leave it or remove it.

 

I simply stand on the shoulders of giants...

 

Somewhere there is good discussion also about "correct jets then" are not maybe "correct jets now" with our fuel blend. We obviously lost Lead in 1977 here in the US.
All that is kind of "over my head"....

I just burn all the Shell Premium I can!

 

Interesting that the 308 GT4 USA jetting almost across the board is more aggressive than the 308 GTB. Mine are currently set lower which I assume has been altered to pass emissions. This is timely as I have already ordered out new jets to address minor sneezing and popping.

 

Thanks for sharing Big Tex!

 

Ferrarichat and this thread is great. Thanks to the many who contributed, I used a lot of info from BigTex and SNJ5 for my research.

It took me a little while to scour through and figure out Weber DCNF basics, and this online Weber .pdf was a great start. In general, the 40 DCNF is a 40mm diameter throat downdraft Weber which can accommodate various "choke" or "venturi" sizes depending on engine displacement. And according to BigTex's chart above, carb'd 308's were equipped with 32mm Venturi's from the factory.

I needed this information for my two carb cars, a 1979 308 GTS USA and a 1980 Euro GTB dry sump (both have stock cams, compression ratio's and free flow exhausts, the GTB is an EPA exempt car)
The US GTS has: 200 Air Corrections, F36 Emulsion Tubes, 125 Main Jets, and 55 Idle Jets with 32 Venturi's, it seems to run fine and clean with this set-up
The Euro GTB has: 200 Air Corrections, F27 Emulsion Tubes, 125 Main Jets and 50 Idle Jets with 34 Venturi's (I was told a prior owner jetted it this way for peakier RPM HP). From what I and tell (and read in F-chat), any upper RPM benefit feels to sacrifice low and mid-range with the larger 34mm Venturi's. Also, it seems the F27 Emulsion Tubes may richen up the entire operating range. I want to bring it back to OEM, so I'm planning on 32 Venturi's with F36 Emulsion Tubes, with likely 135 main jets, with verification of air/fuel mixture on a chassis dyno this spring. (recommendations encouraged...) So far, I have not been able to source the OEM F36 Emulsion Tubes (although I found the F24's which may be a better fit than my current F27's)

BigTex's chart above helps a lot, and he mentioned threads regarding jetting for regional fuels, these F-chat threads have been very helpful, see: 308 Euro Carb Jetting, and Carb Jetting for Euro Fuel. Also, below are a few of the threads that I found helpful in learning how to find parts and jet the Weber DCNF 40's:

https://www.ferrarichat.com/forum/threads/best-jetting-for-webers-for-78-308-gtb.148103/
https://www.ferrarichat.com/forum/threads/calculation-of-carburetor-size-requirements-hard-core-weberphiles-only.147926/
https://www.ferrarichat.com/forum/threads/performance-cams-in-v-8-cars-carb-and-k-jet-continued.232930/
https://www.ferrarichat.com/forum/threads/what-are-the-stock-main-jets-on-77-308.20037/
https://www.ferrarichat.com/forum/threads/euro-carbd-308-ignition-curve.179698/
https://www.ferrarichat.com/forum/threads/ferrari-308-gts-weber-carburetor.471534/

Hope this helps (and hope to get help too)
Thanks,
Paul

 

I'm sure that chart "came from here" originally...glad I could find it....

Recall that the 1975 308GT4 was probably the last Ferrari set up for performance, even in 1976 -77 they were starting to "find ways" to satisfy our US EPA regs, and then catalytic converters arrived in 1978, with much milder camshaft profiles.

Carry on!

 

It "could" still be an ign problem.

Do you have dual dizzies with the mechanical advance?

If one dizzy mech advance gets a little sticky, you have different timing on one bank vs the other. It usually won't cause stumble, or miss, though, just a bit of backfire thru the carbs.

Doug

 

Correct, it's the progression holes that are different, which is largely due to different ignition advance. I argue they make very little difference. The primary difference is the Euro advance setup is a bit more aggressive as they did not have to worry about emissions, but this is easily altered with any US spec carb car. Whatever you do, do NOT swap to F24 emulsion tubes, they allow far too much fuel in the well and even Ferrari went to F36 tubes on later carb cars and most that left the factory with F24 tubes are likely F36 by now anyway. Once the ignition advance is set to advance more aggressively, most carb cars run great with a 140 main jet and 190 or 200 air corrector and are right there with the capabilities of any Euro carb engine.

 

I made that "subset-chart" by cutting and pasting information from pages 185 and 186 of the Haynes Weber Carburetors Owners Workshop Manual (which has the complete chart covering many automobile marques) -- probably back in the FList days .

Chapter 13 is the bible for Weber DCNF carbs.

 

I purchased a set of DCNF F36 emulsion tubes from Pierce Manifolds in Calif. The holes are at the same level in my OEM set, but the holes are aligned from top to bottom. Call them to verify they have the DCNF type.

 

Good to hear, I was going to go with the F24's, but based on what Ferraripilot says above, I will find the F36 tubes and tune to the early GT4 specs for the late Euro GTB. Thanks.

 

Probably need to describe my vocabulary first, to me a sneeze is basically a backfire up through the carb and a pop you can hear coming through the exhaust more like a burble. The popping/burble happens mostly when I took my foot off of the accelerator and basically coasting. The sneeze is just the opposite, this mostly happens immediately after I push the accelerator at lower revs. I am running 55 idle jets and believe that 57 or 60 jets will solve the popping/burble issues along with a minor adjustment to the idle screws. The sneezing, I am hoping to solve for by adjusting the air correctors up to 200, keeping the emulsion tube at 36 and increasing the main jet to 140. Both issues happen low in the rev range, no issues at all while accelerating and at revs above 3000.

 

https://carbcar.com/shop/ols/products/weber-carburetor-f36-emulsion-tubes

One possible source.

 

Maybe someone brought it up earlier, but did "sprint pack" cars come with 34mm chokes? Seems like I remember reading that and it would be logical. P6 cams would definitely move the power band higher and need more flow.

 

This has been gone over many times.
My car was:
60 idles
140 mains
200 air corrections
This on 10 to 1 compression

Standard cams. However, if you want to play with the cams the P6 is too aggressive for street. Go to Cat Cams: http://www.catcams.com/welcome.aspx


They have cams for 308 which bridge the standard and the P6.

 

I certainly wasn't suggesting anyone use those cams....the original question was what the cars came with as far as carburetor specs. I absolutely would have to agree with you. Not only would they be too radical, but cam design as certainly come a ways since the 70's, especially on cams with aggressive ramps. If you are going to replace the early cams, something more modern and less radical would be a wiser choice.