Yea! Confimed probable backfire cause

Yea! Confimed probable backfire cause

odie
odie

August 4th, 2008, 4:11 pm #1

After Matt and his wife picked up my beat up rusted out parts cars, I happened to run int o them again in from of menards. They and another race friend of theirs confirmed that it is DEFIANTLY Running rich. Last Jet sizes were Idles 45's and Mains 130. These are on Dual 42 DCNF's. So here is the question, How Low do I go? I can miss a few times, but at ~$40 for each try, I want to limit my chances of getting it right.


Odie
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Joined: December 18th, 2004, 1:50 am

August 4th, 2008, 9:04 pm #3

My carb is a single 36 DCNF with 40-80 camshaft.

36DCNF 26 Venturi 115 mains 190Aircorrection F36 emulsion

45 Idle jet. Good low end 2500 and power band to about 6500 RPM

TonyK.

TonyK Grimsby Ont Canada.
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odie
odie

August 5th, 2008, 1:03 pm #4

After Matt and his wife picked up my beat up rusted out parts cars, I happened to run int o them again in from of menards. They and another race friend of theirs confirmed that it is DEFIANTLY Running rich. Last Jet sizes were Idles 45's and Mains 130. These are on Dual 42 DCNF's. So here is the question, How Low do I go? I can miss a few times, but at ~$40 for each try, I want to limit my chances of getting it right.


Odie
Idles 40 (35's are available) and 120 mains.

how does one know which is running rich? I am thinking it is the idles as it isnt until I am on the idle circuit with my foot off the gas I get the backfires. So maybe I should go with 35's for the idle?



odie
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Matt Brannon - Midwest X1/9
Matt Brannon - Midwest X1/9

August 5th, 2008, 4:27 pm #5

After Matt and his wife picked up my beat up rusted out parts cars, I happened to run int o them again in from of menards. They and another race friend of theirs confirmed that it is DEFIANTLY Running rich. Last Jet sizes were Idles 45's and Mains 130. These are on Dual 42 DCNF's. So here is the question, How Low do I go? I can miss a few times, but at ~$40 for each try, I want to limit my chances of getting it right.


Odie
Hey Odie,

I noticed a pair of problems on your car when we saw you that day.

First, at least at idle, the car was terribly rich. If its not the jets, its possibly float levels.

Second, I think its been running so rich that you've fouled plugs, the car was definitely running on three cylinders when you pulled away. Pull your plugs and start there to see which ones are black.

As for finding the problem hole, that's a tough one when running rich. Usually when running lean you can hit each hole with some starting fluid
or propane and see if the engine changes tune.

I have seen DCNFs have bad holes that nothing can resolve, even a full rebuild.

Lastly, there's an outside chance it could be ignition, but unlikely. Make sure the plugs are gapped and that you have a solid spark.

-M
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Joined: September 22nd, 2005, 2:52 pm

August 5th, 2008, 4:52 pm #6

Idles 40 (35's are available) and 120 mains.

how does one know which is running rich? I am thinking it is the idles as it isnt until I am on the idle circuit with my foot off the gas I get the backfires. So maybe I should go with 35's for the idle?



odie
Odie, you might want to contact Brad Garska. He has twin 40DCNFs and lives in Saleen/Milan and has an assortment of jets. He is pretty good about helping folks if they ask and he knows the deal.(about hr away from you if I remember correctly).

As for your question you need to tell more information. Your jetting could be fine and your idle screws are set too rich. Please state the following:

#turns of each idle enrichment screw - 1.25turn? (make sure you get an accurate count so you can get them back to the inital setting)
Chokes - 34, 36, 38???
Venturies - 4.5???
Idle Jet - 45F9???
Main Jet - 130?
Air Corrector - 190?
Emulsion Tube - F24?
Pump Jets - 45??? (list the entire designation)
Float setting - 12mm?? (I don't have any idea what it is for a DCNF)
Fuel pressure - 3psi???

Finally check each plug and note the color of the tip, wet, black, white, or tan.

Peace,
Brian


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odie
odie

August 5th, 2008, 5:33 pm #7

Hey Odie,

I noticed a pair of problems on your car when we saw you that day.

First, at least at idle, the car was terribly rich. If its not the jets, its possibly float levels.

Second, I think its been running so rich that you've fouled plugs, the car was definitely running on three cylinders when you pulled away. Pull your plugs and start there to see which ones are black.

As for finding the problem hole, that's a tough one when running rich. Usually when running lean you can hit each hole with some starting fluid
or propane and see if the engine changes tune.

I have seen DCNFs have bad holes that nothing can resolve, even a full rebuild.

Lastly, there's an outside chance it could be ignition, but unlikely. Make sure the plugs are gapped and that you have a solid spark.

-M
Will get new plugs on the way home. (I could clean the old ones, but I am too lazy)
I will double check float levels.
Will also check fuel pressure.

We used propane when we balanced them out when I first put them on.

Still planning on the honda swap, but would like it running better till then.


Odie
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odie
odie

August 5th, 2008, 5:36 pm #8

Odie, you might want to contact Brad Garska. He has twin 40DCNFs and lives in Saleen/Milan and has an assortment of jets. He is pretty good about helping folks if they ask and he knows the deal.(about hr away from you if I remember correctly).

As for your question you need to tell more information. Your jetting could be fine and your idle screws are set too rich. Please state the following:

#turns of each idle enrichment screw - 1.25turn? (make sure you get an accurate count so you can get them back to the inital setting)
Chokes - 34, 36, 38???
Venturies - 4.5???
Idle Jet - 45F9???
Main Jet - 130?
Air Corrector - 190?
Emulsion Tube - F24?
Pump Jets - 45??? (list the entire designation)
Float setting - 12mm?? (I don't have any idea what it is for a DCNF)
Fuel pressure - 3psi???

Finally check each plug and note the color of the tip, wet, black, white, or tan.

Peace,
Brian

<>
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Joined: December 18th, 2004, 1:50 am

August 6th, 2008, 1:39 am #9

Hey Odie,

I noticed a pair of problems on your car when we saw you that day.

First, at least at idle, the car was terribly rich. If its not the jets, its possibly float levels.

Second, I think its been running so rich that you've fouled plugs, the car was definitely running on three cylinders when you pulled away. Pull your plugs and start there to see which ones are black.

As for finding the problem hole, that's a tough one when running rich. Usually when running lean you can hit each hole with some starting fluid
or propane and see if the engine changes tune.

I have seen DCNFs have bad holes that nothing can resolve, even a full rebuild.

Lastly, there's an outside chance it could be ignition, but unlikely. Make sure the plugs are gapped and that you have a solid spark.

-M
One problem that haunted me with the DCNF as it got older and went through a lot of heat cycles is that the top of the carb became warped. With the engine hot and shut down, look into the barrel and see if you can see fuel bubbling at the parting/gasket line of the top of the carb. if it is then the top is warped or the gasket has compressed to thin to seal. This will constantly allow fuel to dribble into the barrel and run a rich idle.

TonyK.

TonyK Grimsby Ont Canada.
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odie
odie

August 6th, 2008, 2:40 am #10

Odie, you might want to contact Brad Garska. He has twin 40DCNFs and lives in Saleen/Milan and has an assortment of jets. He is pretty good about helping folks if they ask and he knows the deal.(about hr away from you if I remember correctly).

As for your question you need to tell more information. Your jetting could be fine and your idle screws are set too rich. Please state the following:

#turns of each idle enrichment screw - 1.25turn? (make sure you get an accurate count so you can get them back to the inital setting)
Chokes - 34, 36, 38???
Venturies - 4.5???
Idle Jet - 45F9???
Main Jet - 130?
Air Corrector - 190?
Emulsion Tube - F24?
Pump Jets - 45??? (list the entire designation)
Float setting - 12mm?? (I don't have any idea what it is for a DCNF)
Fuel pressure - 3psi???

Finally check each plug and note the color of the tip, wet, black, white, or tan.

Peace,
Brian

Chokes - 32
Venturies - 3.5
Idle Jet - 45
Main Jet - 130
Air Corrector - 180
Emulsion Tube - F22
Pump Jets - 40
Float setting - 53mm
Fuel pressure - need to get a gauge
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