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Old 07-24-2013, 05:23 AM
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carb adjustment?

I'm new to performance engines and stuff. I have a mild built 350 with a demon carb. Car runs good but when you're at a slow speed and punch it car has a bad hesitation and almost dies but if you ease into it car runs well. Any help will be appreciated. Thanks.

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Old 07-24-2013, 05:31 AM
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Quote:
Originally Posted by jriley82 View Post
I'm new to performance engines and stuff. I have a mild built 350 with a demon carb. Car runs good but when you're at a slow speed and punch it car has a bad hesitation and almost dies but if you ease into it car runs well. Any help will be appreciated. Thanks.
Start w/the accelerator pump. Look into the front two barrels and see if there's an immediate squirt in both sides from the shooter when you open the throttle.

More here.
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Old 07-24-2013, 08:58 AM
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I'm not familiar with the demon carburetor, but it appears to use step-up springs that are similar to the Edelbrock 1406. If that is true, then to resolve a part throttle bog you should start out by trying a step-up spring that is rated at a higher vacuum. Do this before you change the accelerator pump settings.

The rating on the step-up spring represents the vacuum level where it transitions the rods from cruise to power. Stock springs might be rated as low as 4" and they create a lean bog because the rich mixture comes in too late as you hit the throttle. You can get springs rated up to about 8", which will make the power transition happen much quicker as you push down the throttle.

Once you get the transition to work right, you can try different rod combinations to see if you can improve the power. All the rods have a stepped design with two different diameters (cruise and power). This affects the flow through the jets based on whether they are pulled down by vacuum (cruise mode, large part of rod in the jet) or pushed up by the springs (power mode, small part of rod in the jet). Smaller diameter rods allow more flow through the jets, so you swap to smaller diameter rods to get more fuel.

Springs and rods can be changed very easily while the carb is mounted, using only a screw/torx driver.

If the demon is designed like a Holley, then all my comments above don't apply.

Bruce
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Old 07-24-2013, 10:32 AM
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Quote:
Originally Posted by jriley82 View Post
I have a mild built 350 with a demon carb.
Hold on a minute... do you have a "Holley" Demon:


or a "Thermoquad" Street Demon:


The new 'Street Demon' carbs use step up springs and metering rods. The older style Demons are just like a Holley as far as tuning, etc. goes with a few differences like the Idle-Eze setup. The link I provided in my first post addresses the Holley type accelerator pump.
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Old 07-24-2013, 11:26 AM
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It's also possible your timing is set a tad too low. Check it just to be sure it's not on the low side. or even advance it a couple degrees and see how it does. Do you have a different carb you can put on and see if it does the same thing?
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