46Wheezy: The newer Holleys have power valve blow out protection built in. Mine was new in 1978 -- ran 25 years on my last engine and got a quick rebuild for this next mill. We added a 50cc accelerator pump on it before the last engine went down in 2002, and that solved a lot of bog problems off the line. The older Holleys are more susceptible to backfire knocking out a $7.00 power valve. [Not to mention the gaskets, O-rings and spilled gas used up everytime you R&R a Holley]. There is a gizmo that involves a drill bit and a micro-sized
"power valve restrictor" but I don't want to mess with that. The carb had been set up with an 8.5" Hg power valve. I was out of replacement 8.5s, so we tried a 6.5" Hg power valve and reassembled the carb. Theory being that a later opening power valve would be a step toward better fuel economy. It started up OK, ran at a lower RPM and a few inches of mercury lower than optimum, but seemed ready otherwise, so I tried a test hop. As stated in my last post, it flunked. One symptom of the problem is that I'm getting 120 miles to the 20 gallon tank. 6 MPG is 454 territory, a 292 should get at least twice that even with a lead foot. One possibility for the manifold vacuum instability could be a warped carb base plate. (Factor the siamesed exhaust/intake configuration with Tucson summer heat x 25 years + 250,000 miles-- much of it off-road). For whatever reason operation has not yet stabilized. A new throttle base plate costs about $130. A whole new 4160/8007 Holley 390 CFM carb costs about $289. My friend who usually helps me tuning Holleys, is incommunicado. Well, that and the used car dealer he bought his '98 Dodge Dakota pickup from used some non-Mopar approved anti-freeze and it thrashed the entire heating & cooling system: heater core, radiator, thermostat, under dash leaks, etc. So whatever -- he's busy.
That leads me to consider carb alternatives:
The Barry Grant _Road Demon Jr._ at 525 CFM is a 'cute' billet 4160 clone, for only $260. But I hear they're sensitive to atmospheric changes and have to be tweaked continually. Maybe too much like a Holley.
Jegs' also lists a 450 CFM Holley 9766 4Bbl for only $188, but it's chokeless (and still a Holley).
I have run Carter AFBs on my V8s with good results. A 750 CFM on the 454 in my former ride, a '67 K/10 Suburban, and a 600 CFM on the 350 in my current daily driver, a '71 GMC K/5 Jimmy. I like the AFB design for its robust simplicity and field -servicable nature.
Unfortunately Edelbrock bought Carter out. Edelbrock chose not to continue making a 400 CFM AFB. Closest to it is the 500 CFM Performer EDL-1404 for about $225. Checker Auto did not have one in stock today, so I didn't get one yet. I may mail order. Depends on bottom line. They are supposed to be drivable right out of the box -- unlike any Holley I've ever had -- if a little rich at first. Also the Idle mixture screws would be sited on the left, facing the drivers side fender, a very handy place for tune ups. A carburetion site had a program to crunch numbers of RPM x CI and it spit out that my ideal flow rate would be 408 CFM. I'm hoping 500 will not be too much. A few other bored-out 292 4Bbl users have stated their satisfaction with the AFB, so I'm optomistic.
Sorry for the novel. HTH
