Coked Up


I have been a Mopar Action reader since 1991, I absolutely love your tech and other articles. My daily driver is a 1972 Valiant which looks like the one Dennis Weaver drove in “Duel.” It is acting up, and it’s driving me crazy. Here’s its specs:
Originally a 49-state car, stone-stock 318 2-Bbl. 904 w/Trans‑Go kit, stock 2.71:1 gears, NGK plugs gapped @ .040, 8mm Accel wires, Pertronix transformer, Orange
Box amplifier. 195° t‑stat, stock 22˝ rad with factory shroud, 5‑blade fan w/clutch (originally had H51 A/C, but didn’t work, so I removed it).
I burn only premium fuel (which is an anemic 91 octane here in CA), I allow the engine to warm for about 3‑5 minutes on cold mornings, and then drive s‑l‑o‑w‑l‑y until the temp gauge starts to rise. The problem: It sputters and coughs wet carbon out of its pipe, at operating temp or not; the right‑bank plugs get carbon‑fouled, whereas its left‑bank plugs are fine.

The EEC canister was disconnected/ removed due to cracks and the resultant vacuum leaks, and the ‘CARB’ or ‘BOWL’ line from the carb is connected directly to the hard line that goes to the fuel tank. The fuel cap is fine as it’s only 3 years old. Yes, the distributor’s vacuum advance is hooked‑up properly (it goes from the canister
to the carb’s air horn, just as original). Any ideas? Power is down, fuel mileage is in 440 territory. This is killing me financially.

The manifold heat control valve (in the R/S exhaust manifold) is stuck closed, for sure. Free it up with repeated shots of Mopar P/N 4318039AC solvent (PB Blaster may also work). If you are lucky, the exhaust valves aren’t yet burned. This malady was a much more common occurrence in the leaded fuel days, but hasn’t gone away completely by any means. Also, at some point, be sure that the choke flap is opening fast enough. When this crossover/heat-well system sees a lot of mileage, what will sometimes happen is that
the crossover passages in the heads and intake manifold floor become coked up (like the nostrils of a major sports, movie, or rock star, only in this case, the passages become clogged, not reamed out). Now the choke
thermostat sees heat much more slowly, so the choke stays on much longer—only making the problem worse. The “book” authorized repair is a teardown (heads and manifold) and carbon cleanout, the E-booger “make it work” method is a simple hand choke installation.

0 0 vote
Article Rating
Notify of
Inline Feedbacks
View all comments

This website uses cookies to improve your experience. We'll assume you're ok with this, but you can opt-out if you wish. Accept Read More

Would love your thoughts, please comment.x