Replace ’77 Lean Burn

Tech Question


Kevin McKinney, Wichita, KS, 1977 Chrysler Brougham 400

Oh great GURU of Mopar Tech.
I know most folks have no respect for the the 5500 lbs cruisers, but sheonly has 29,542 miles on her clock. And is very comfortable. To the point: Ireplaced the Lean Burn with the standard ECU and distributor ect.
The ThermoQuad, as you know, has no port for the vacuum advance. This isnot a problem on anything else in my stable: ‘Cuda, Chargers, and the 19663/4 ton Hemi Power Wagaon. But with the weight and sorry gas and the ACrunning, to be good to her I think she needs the advance to work. If I tookthe base plate of the the carb would it be possable to drill and press in acut off niple from a junk carb? If so what size bit/hole for the orfice, andhow deep…just to the passage? I can do the press fit thing on the nipple.I read an artical some years ago I think it was Mopar Action where someonesent their carb to a shop in California and had it done. I am a machinist/tool maker ect., so tools and stuff wont be a problem. Can you give someengineering info or specs, drawings, ideas? I haven’t taken another carbapart to have a look and see yet. This carb is like new 29,000 miles and theshafts are tight ect. So I would like to keep it on there. If any one wouldknow how it would be you!

Thanks Kevin


Kevin, it can be done, but it is a bitch…it’s a transfer slot, actually.Look at any non-ELB carb and you’ll see.

Here’s the near-zero-buck way to get around this: Take a length ofsuper-small “hobby shop” copper tubing and rig it up so it points downeither primary barrel, ending just barely above the rear edge of thethrottle plate. You’ll have to rig up mounting and probably notch the chokeplate, but this is still way easier than modifying the throttle body. Thetop of this new tube = ported spark for vacuum advance cannister. To test,there should be zero vacuum at idle, and plenty when the throttle is heldopen slightly.

Now tune the vacuum advance. I’ll bet that 8.2:1 mill can handle a totaladvance (initial + mech + max vac.) of almost 60 degrees at light throttlecruise. The more the better! The engine will last longer (no fuel wash, lotsless carbon) and fuel economy will increase by a large amount — possible asmuch as 30-50% (over having NO vac. advance). Help starve an oil baron!


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