[BEB]

Hi, I am from the UK and new to this site. I have a Cobra replica which isn't running quite right? Please can you help me.

I have a Street Avenger 770 on my SBC 409ci, Edelbrock Performer RPM intake, Dart Pro One aluminium heads, Comp Cams 268 hydraulic cam, MSD 6AL, Holley Powershot air filter. Manifold vacuum at idle approx. 15 Hg.

Jetting is 'out of the box' 72/75. 10.5 power valve. Green pump cam; no. 1 position. Std. plain vacuum spring.

The problem is that there is a slight hesitation on light throttle from idle to 2000 rpm. I have an air fuel ratio analyser fitted so I know for certain it is leaning off for a moment or two before it 'picks up' and the mixture goes to back to where it should be - i.e. around 14:1. The obvious thing to do is increase the pump nozzle, but I've tried that going from .025 to 028 to 031 to 035 - it seems to prefer .028 as going bigger doesn't seem to make any difference. I also tried raising the primary float level slightly, but that hasn't cured it either.

What should I try next? Should I be looking at richening up the idle transition circuit. Would it help adjusting the position of the secondary throttle plates. I'm reluctant to richen up the primary jets because they are already on the 'rich side' according to my air/fuel analyser. Should I try a lower opening power valve? But, surely that would make the problem worse? Would a different colour pump cam bring more fuel in sooner - if so, which colour?

Anyway, please help me as it is a mystery why I am finding it so hard to dial this carb in !

Thank you and best wishes,
Simon Winfield.