I have a freshly rebuilt 302 in my 85. It has a rebuilt set of Dart Windsor heads with a fresh valve job and springs. The Cam is a Factory HO roller cam. Ever since I put this engine together it has had a problem with backfiring through the intake below 2500 rpm. It does it when I open the throttle as if it doesn't have enough accelerator pump shot.
The car is running a Megasquirt fuel injection with a Holley 4barrel throttle body injector atop a Weiand Stealth intake manifold. The Megasquirt and intake was on the car before the engine rebuild but didn't have the backfiring problem with the previous engine. In troubleshooting the problem, this is what I have done...
- Added acceleration enrichment until the car would stumble from being rich on acceleration
- Loosened the valves until they were clacking thinking I might have had a valve too tight
- Adjusted the distributor phasing thinking the spark was jumping between cylinders
- Installed a Holley 4010 600CFM double pumper which was on the car before the Megasquirt
None of these things have been able to alleviate the problem. When I datalog with the Megasquirt it does show the engine going very lean as the throttle is being opened but then quickly goes rich to between 11-12 AFR. This is true both with the Throttle body injection and carburetor.
Can anyone offer me some troubleshooting advice? I have exhausted all my troubleshooting knowledge.
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