UK emissions IVA. Carb problems 850DP. Holley (which) or ???
Getting very frustrated with the carb now having spent many hours working on it and also reading up on how to set up, how to rebuild, how to diagnose etc etc so hoping you guys can help out.
I'm having troubles getting current carb which was supplied with engine about 8 years ago (supposedly new Holley 850DP 0-4781-6) to run properly at idle. Fuel flow into engine from carb just doesn't seem to work properly but no previous knowledge of Holleys to gauge it against. We have tried rebuilding, checking every orifice, new gaskets, replaced power valves, secondary linkage disconnected, secondaries properly closed, even swapped round metering blocks. Next step is power valve blanking plugs and trying smaller main jets, just to try to eliminate them from the investigation. Sometimes runs ok but not great, sometimes just runs horribly. Idle adjusters have only very little impact on how it runs. Engine only running in garage, not on road. Fuel pressure consistent 6psi, fuel levels in float bowls good. We are wondering if we just got a dud carb? When blipping the throttle the fuel (from accelerator pump?) just seems to 'drop' onto the throttle bodies (I have heard of Holley DPs described as fuel toilets, is this what they mean?)
Engine is quite wild 396, 4.100 bore, 3.75 stroke, Yates C3, Ford SVO dry sump only block.
Block is 1993 so looking to get down to 4.5% CO2 at idle.
Firstly, any clues what might be wrong with the carb?
Secondly, Is there any hope of getting this combo down to 4.5% at idle?
Thirdly, if not what would be the best/simplest way to achieve it for the test and for future MOT tests? 600 4150 with vacuum secondaries, or 4160 Street Avenger, or 370cfm, or Edelbrock, or ??? Could swap to this for each MOT and go back to the 850DP (if we can get it running sensibly) or something else more sensible for the rest of the year. Therefore would prefer to use same inlet manifold etc.
Thanks very much for any help.
Lee Stanley DRB #52 under construction