I'm not sure a Holley Street Avenger is overall a good solution considering some of the issues you mentioned. Assuming you have a fairly healthy cam in the engine - and your comment that turning the idle mixture screws did not affect it - the primary throttle blade is probably opened too far at idle to allow the idle circuit to work properly.
At hot, curb idle the primary throttle blade should rest in the middle of the little transfer slots in the side wall of the bore. That creates the vacuum signal that pulls fuel through the idle passages. If blade rest at the top of the slot or above it, it loses it's vacuum signal and basically you have no control over the idle mixture.
A possibly work around is to look at the underside of the base plate and see if there is a small adjustment screw that's a stop for the secondaries to close. Usually Holley has one to avoid the secondaries from closing completely and possibly sticking in the bore. That screw can be adjusted to open the rest position of the secondaries slightly to pass a bit more air at idle. That will allow closing the primaries down at curb idle so the blades rest in the proper position. You should get a lean roll off at hot idle when turning the mixture screw all the way in and some rich effect when turning it way out (fall off in rpm, engine vacuum, rich smell).
But the idle mixture circuit only works at closed throttle. As soon as the throttle is opened the transfer cirucuit takes over and in most Holleys (and I'm pretty sure the Street Avenger) it isn't adjustable. It's controlled by air bleeds and while it can be modified through trial and error process, it's not a user-friendly process. That is probably where your car is running rich and a new carb is unlikely to do anything about that. That is where going to something like a Quick Fuel Holley-pattern carb becomes a good idea - because the transfer system is tunable. Holley may have some newer models in the higher price range that are now tunable - I don't know.
After the transition circuit, as the throttle opens further the carb picks up the load through the primary metering system and it's tunable by the primary side jets. But it's usually that idle and transition circuit that create a lot of the richness issues that everyone struggles with.
Quote:
Originally Posted by BAsque1
Bill, unfortunately I don't have the specs other than it is a 427 Side Oiler, I know it has a 770 Holley Street avenger, and that is what I purchased to replace the old one, the rebuilding was quoted at about $300.00 the new one is $367.00 so that was a no brainer.
The present carb is too rich and I have not been able to adjust it to a leaner mixture--no effect when we turn the screws. the bowls were checked and that is fine, but I am still getting a very rich mixture.
My gas mileage went down from 11-12 to about 8 MPG, not that this will break me but, it tells me that there is something wrong. I removed the electric gas pump and left the OEM mechanical so I get between 5- 5.5 lbs as it should vs 9 lb that I was getting before.
I use very good gas BP 93 octane or Shell 93. I used a bottle of Techron a while back without much change, the in line gas filter is new and now I installed a new Fram filter when I removed the electric gas pump.
Before it gets to normal temp (180 F ) the mixture seems very rich. The manual choke is working fine and the secondaries are also working fine. Long story short I decided that I would change it.
Regards
Lou
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