Flat Spot/Hesitation

[JMF]

Hi guys got a 70 Charger with a 383, not had it long so just trying to get it running right , I just fitted a new Holley carb(pic below), it runs fine and cruises ok but on full throttle there's a hesitation/flat spot about midway through if flooring it, doesn't seem to do it if I slowly accelerate up to full throttle, it's just that same bit like when if you're in 3rd gear and floor it to Kickdown or flooring it from a standing start.

Does anyone know what the correct settings are for one of these carbs ? Also the timing

Just to add the car smells very rich and fuely and also may be my imagination the fuel consumption seems worse than it should be

Anything else I can check ? As I say it runs and idles pretty good and cruises fine, doesn't seem to be down on power or anything, just full throttle it seems to struggle with the annoying hesitation.

Apart from the carb and headers it's fairly stock from what I can tell , no electronic ignition or anything

Many thanks for any help



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[bee1971]

Sounds like possibly a heavy spring on the vacuum secondary - I would start there and see if this helps

The quick change housing cover that you have makes changing springs a breeze

You just need to remove the top two screws on the black cover , not the whole assembly for spring changes

Read this

https://www.hotrod.com/articles/how-to-custom-tune-holley-vacuum-secondary-carb/

[flyinlow]

Ignition first:  with the vacuum advance unit hose disconnected and plugged, shoot for a ballpark 10* BTDC idle timing . Centrifugal  advance will add 20-25 degrees more  buy 4000 rpm with a stock distributor. Total of 30-35*. When you replace the vacuum advance hose it will add more timing during part throttle acceleration and cruise. These numbers can be messaged to increase performance.

Next make sure your choke is fully opened when it should be. No vacuum leaks: bad hoses ,carb bolt tight.

Next check the float  bowl fuel level: With the engine idling the fuel levels should be about half way up the two little round sight glasses on the passenger side of the carb.

Next check your carbs accelerator pump discharge. Look down the front carb bores as you open the throttle looking for fuel squiring. This can be done with the engine off. If you test it too many times with the engine off you can flood the engine, making it hard to start.

If all these are OK , the secondary vacuum chamber spring might not be the one you need ,causing the secondary's to open before the engine can use the extra air/fuel. ( it boggs)

[b5blue]

Be certain the pump activates instantly, zero gap to throttle linkage.