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Old 04-22-2006, 09:54 PM
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Calling BG Tech...

Last summer my SBC 355 with a Mighty Demon 750 started poping through the exhaust on hard acceleration. The poping would come and go. During the winter it never poped. Now that the weather is getting warmer the pop has come back? Car seems rich at idle. And I get black smoke on hard acceleration. What caused these symtons?

Thanks....

Dave

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Last edited by black66; 04-24-2006 at 10:20 AM.
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Old 04-24-2006, 10:20 AM
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Yo BG Tech

Any thoughts BG Tech????


Dave
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Old 04-24-2006, 10:31 AM
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It is too rich and fouling a plug. My Demon does the same thing.
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Old 04-24-2006, 12:40 PM
Technical Support Barry Grant
 
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Quote:
Originally Posted by black66
Last summer my SBC 355 with a Mighty Demon 750 started poping through the exhaust on hard acceleration. The poping would come and go. During the winter it never poped. Now that the weather is getting warmer the pop has come back? Car seems rich at idle. And I get black smoke on hard acceleration. What caused these symtons?

Thanks....

Dave

Dave,

It's too rich. The warmer it is, the less fuel an engine is going to need. So when its cold outside the engine wants more fuel. Sounds like you need to go down some on your jetting, and possibly the float level. Also, from winter to summer you may need to go in slightly on your idle mixture screws.
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Old 04-25-2006, 11:55 PM
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carb

Thanks for the reply BG. On the idle mixtures screws is there a minium amount they need to be screwed out in order to run? I have all four mixture screws about 1 out and the car is running great.. Before they where closer to 2 - 2.5 out.... I always thought my car started right up when it was cold but I now understand it was to rich and would idle even when cold with a simple blip of the throttle. With the idle mixture screws in more it will not completely idle until it is around 165 F on the temp.


Could you give me a quick Mighty Demon 101 refresher course :

Are the idle mixture srews only for idle or do they do something else with the carb function?

How does the float effect performance if to high or to low?

What jet sizes would be recommended for 5000 ft elevation?

And here is my current setup:

SBC 355
Mighty Demon 750
Comp Hydraulic Roller Cam 254 durations .640 lift intake/exhaust
Camel Hump 2.02 heads
Torker II intake
3200 stall
3.73 gears

I am patiently waiting for my new AFR Comp 195 heads and will install a RPM Air Gap intake. With the new ARF heads and Air Gap intake is there a chance I will have to rejet my carb once again??

And with the Air Gap intake would you recommend a 1" , 4 hole spacer?

Thanks....

Dave
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Old 04-26-2006, 06:08 AM
Technical Support Barry Grant
 
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Quote:
Originally Posted by black66
Thanks for the reply BG.

On the idle mixtures screws is there a minium amount they need to be screwed out in order to run?
There is not a set amount the mixture screws should be. On some applications if you're less than 1 full turn out it can cause a stumble under light acceleration.

Could you give me a quick Mighty Demon 101 refresher course :

Are the idle mixture srews only for idle or do they do something else with the carb function?
Yes, and no. The curb idle mixture screws just control the volume of fuel coming out of the discharge ports in the baseplate. Now this is where the engine should get all of its fuel to idle, and it is also where the engine will get the majority of its fuel for low RPM cruising around. So if you're idle is off it can affect your drivability, and cruising.

How does the float effect performance if to high or to low?
The float bowls store all of the fuel to feed the carburetors circuits. Higher float levels will be slightly richer, and will start the main circuits sooner. Conversely lower float levels will be a little leaner, and will delay when the main fuel circuits start. If your float levels are too low you can run into stumbles from the fuel circuits not starting soon enough. Float levels too high can lead to flooding situations when cornering or braking.

What jet sizes would be recommended for 5000 ft elevation?
I'd go down 3 jet sizes in both the primary, and secondary side of the carburetor.

I am patiently waiting for my new AFR Comp 195 heads and will install a RPM Air Gap intake. With the new ARF heads and Air Gap intake is there a chance I will have to rejet my carb once again??
Most likely you will need to do some re-tuning. It's hard to say how much exactly.

And with the Air Gap intake would you recommend a 1" , 4 hole spacer?
If you're going to run a spacer on this combination a 4-hole should help the bottom end, and drivability.

Thanks....

Dave
Please let me know if you have any other questions.
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Old 04-26-2006, 08:44 PM
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carb

BG I have already jetted down 4 jets sizes from stock jettings. Maybe I need to go down 2 more jet sizes??. So far just from turning the idle mixtures the car is running much better. I am going to lower the floats a little to see if they will help as well. Thanks for quick response......!!!!

Dave
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