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Old 06-22-2007, 09:00 PM
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Demon Carb Off-Idle Stumble - Help

Hey guys

just threw a speed demon 850 dbl pumper (slightly used) on my BBC. Works great except for the ever popular "off-idle stumble" during "light" acceleration.

Not sure where to start. Idle is about 1000 rpm in gear with foot on brake, The float levels are correct, the primary butterflies appear to be almost fully closed, I'll assume the squirter works (but I will check it), the idle mixture screws are backed out about 1.5 turns, other than that what should I do next - where do I start?

thanks.

Lee

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Old 06-22-2007, 10:08 PM
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the transition slots should be opened about the size of a square... you would need to take the carb off and look underneath on the primaries side to see the slots. other than that, the squirters could be too rich or too lean. i'd check the transition slots first though. it's all described in the instruction manual that came with the carb, or you could possibly read/download it from the demon website....
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Old 06-23-2007, 11:17 AM
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If you have a set of accel pump cams, you could try a more aggressive one. That's what helped me. THe pink that comes in the carb is pretty linear, you could try the orange or black or blue (most aggressive) and see what that does.
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Old 06-23-2007, 11:50 AM
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What cam, what intake manifold? What is the initial timing @ idle?
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Old 06-25-2007, 06:14 AM
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Quote:
Originally Posted by leejoy
Hey guys

just threw a speed demon 850 dbl pumper (slightly used) on my BBC. Works great except for the ever popular "off-idle stumble" during "light" acceleration.

Not sure where to start. Idle is about 1000 rpm in gear with foot on brake, The float levels are correct, the primary butterflies appear to be almost fully closed, I'll assume the squirter works (but I will check it), the idle mixture screws are backed out about 1.5 turns, other than that what should I do next - where do I start?

thanks.

Lee

Lee,

If the engine doesn't stumble under a hard acceleration, your accelerator pump circuitry is most likely OK.

A few questions for you:
1) What type of intake manifold, & camshaft are you using?
2) How much initial timing are you running?
3) How much vacuum is the engine producing at idle?
4) How much of the primary, & secondary transfer slots are exposed right now?
5) Where do you have the float levels set in the windows?
6) Lastly are there any times the problem is better or worse?
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