40 dcnf weber question

docpan said:
I was having a very lean idle but above 3000rpm it was perfect. Changed to a 65 idle jet and thing are much better. No stumble off idle.
200 ac
F24
130 main
32 choke
4.5 aux Venturi
I don’t know what the pump jet size is.
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I had a similar issue but found that using F36 emulsion tubes solved the problem.

Weber 40DCNF 47 7L, Sprint Manifold

Choke: 32mm
Auxiliary Venturi: 4.5mm long
Emulsion Tube: F36
Main Jet: 1.35mm
Air Corrector Jet: 2.20mm
Idle Jet: .55mm
Idle Air Orifice: 1.6129mm (measured)
Pump Jet: .45mm
Pump cam type: 11
Float Level: 50mm
 
Jimgkioulis said:
all 40 and 42 44 have problem at 2000-2800rpm. only 36 dont hve that
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I'm curious, does that include all of the various venturi options as well? For example, how about a 40 DCNF with smaller venturis vs a 36 DCNF with the same venturis? Not to mention all of the other possible differences; emulsions tubes, jets, pumps, etc, etc...are they comparing like with like? Or is there a fundamental design difference with the 36 vs all the others that cannot be accounted for by all these factors?
 
i do everything. the best is dcnf 36. i have put dcnf 36 and 40 and 42 and 44. this is my job. the best is 36. if you tunning some put 32 venturi. 50 inde. 185air f36 ever and 135full. dcnf 40 everything seting you do nothing... the prroblem is ever the same. the body have problem inside. i see the at site ferrari and tell nothing with ferrari go 2000 2800rpm max. allgo up 4000. the diference betwen dcnf 36 40 at hp is 4 hp up 4500rpm. at low rpm is the same and little down than 36 dcnf. better than dcnf 40 is idf 36. have and this 4-5hp diferent than 36 dcnf but atlower rpm 2500 and up. i have idf 2 years now i think. dcnf 36 i job and 40 15 years....40 is sut. 36 you love it..... really! the best.
 
I have run my 40DCNF12s on a hot 1300 and hot 1600.
No problem between 2000 and 2800 rpm. Especially not the 1600.
I did have a problem like that with both engines when I ran the PBS header because of reversion effects.
A well built 1900 with 42 or 44DCNFs makes more torque at 2500 than a 1500 at 4000rpm.

There is no inherent problem with the carbs.
Yes, you can have a problem like that that might go away with the change to smaller carbs, but it may just be a problem with the rest of the motor that is masked by using a smaller carb.
An engine setup is always a combination of many factors and many parts.
Problems found on one engine setup should not be generalized and stated as gospel.
 
"There is no inherent problem with the carbs.
Yes, you can have a problem like that that might go away with the change to smaller carbs, but it may just be a problem with the rest of the motor that is masked by using a smaller carb."

I have had 40DCNF's on my car for 28 years. Once set up they work without issues. No hesitation at transition from idle to main , very smooth thought the rev range. Even idles at ~1000 rpm with 42/82 cam. I can't say other carbs such as 36DCNF's or IDF's etc. don't work as well since I have never tried them.
 
As I have mentioned in the past, I am a total convert on using an air/fuel gauge. Without it you are just pissing in the wind trying to figure out carb issues.
 
carl said:
As I have mentioned in the past, I am a total convert on using an air/fuel gauge. Without it you are just pissing in the wind trying to figure out carb issues.
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Remember the old days before wideband O2? Reading plugs, experimenting with the "ColorTune" gadget, seat of the pants tuning, pretty much all trial and error. And that was pre-internet so we didn't even have the advantage of sharing the experiences of others as a guide. For a premium price you could buy a pre-jetted carb kit from some vendors. It was a generic tune (at best) but it beat not knowing what the heck was going on. I guess someday we'll be laughing at the barbaric idea of using a wideband O2.
 
Yes, they will be laughing because they will all be driving electric cars. All the old guys who "tuned" slot cars in the day will be in high demand!

Can't wait to see what NASCAR racers will look like in 20 years...modern bodies with "ancient" gas fueled V-8s and no spectators since by then everyone will be in their virtual reality worlds and "racing" cars themselves. I have tried to watch a few e-car races on TV and the just don't work for me.

Sorry for yet another vector off topic.
 
Correct, I welded in a bung on the Bertone header and the header on the 77 already had a bung installed.
 
Temporarily living in Vegas from SoCal, I go back and forth between them now and then. I get a laugh every time I see a Tesla on the back of a flatbed halfway in between, having run out of power after not realizing the trip is longer than the charge allows.
 
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