Help with carb tune

[Green429]

I recently had my car dyno tuned. Pretty happy with the results, 398HP and 400 lb-ft at the wheels. Two months later and at 4000 rpms the power seems to fall off a cliff in 3rd and 4th gear. In 1st and 2nd it runs beaufifully. Also feels like the engine is either getting starved or flooded. The power curve from the dyno run was very flt from 2700 - 5800 so this doesn't make sense to me.

I'm hoping not to have to pay for another tune so I'm looking for suggestions on what to look for.

The carb is an Edelbrock 800 cfm. Not looking to go to a Holly or other carb, so lets not go there.

TIA,
Gregg

[Todd Buttrick]

800 CFM seems a bit big for that HP. If you're set on keeping that carb, you may have a hard time tuning that out and if my memory serves me correctly, there have been very few roadster owners (if any) who are happy running a Rochester type carb. Why are you so resistant to make a change?

[Dan Dixon]

Do you have any tools such as an Innovate Air/fuels meter or gauge? You can plug an O2 sensor in to your J Pipe and run the car like normal and have someone record your ratios at different RPM's and at different engine loads. This will help. An A/F ratio of 12.5-14.5 is close to ideal. Not sure what vacuum you have at slow engine speeds but the larger carb could be hurting you a little when it comes to total manifold/carb velocity but that doesn't really matter if you never experienced the problem before. Is this a new problem? SOunds like it might be but I couldn't tell. Tell us more about your engine also do you know your timing curve is at what RPM?

[3kcarbon]

A 800 is a bit big for that HP range,. Mine is rated at 340HP and I put a 670 Street Avenger on it and had to jet it down some. I'm all about too much is just right but some times it is.