1970 Cadillac Fleetwood carbon buildup

I have a 1970 cad. builds up alot of carbon, what can I do?

There may not be an economical solution if points plugs and condenser have been replaced along with plug wires, distributor cap and rotor and an old mechanic have been involved. Your engine is old enough to need an overhaul. Without details, nobody can start to guess how to answer the question.

How much oil do you use? What’s the compression? Is the exhaust smoking? Grey or black?

Where does the carbon build up?


Hi TeddyInternet:
I too am curious where you see the carbon building up.

Is it building up on the spark plugs causing them to foul?

I am going to guess you mean carbon buildup in the combustion chamber as was common in that era of big cubic inch engines that saw little high RPM use.
I would go with a compression test first, if within spec then proceed. I don’t know if still produce, but there were treatments that you poured through the carb until the engine died. Then let sit ten or more hours, then restart. Produces a lot of smoke. You could Google carbon buildup treatment.
Best way, pull the heads, have a machine shop recondition the heads.
Again guessing your engine might be running too rich, or burning oil.
So depends on how much you want to spend.
Me, if funds are available.
Complete rebuild of engine.
Hardened valve seats
Conversion to TBI
Install high performance ignition system.
Sources: Edelbrock, Accel, et al.
Or replace the engine with a 502.

My 1984 Chevy Cavalier did some preignition knocking when accelerated at speed. The timing advance was OK so I assumed carbon in the combustion chambers and started using Marvel Mystery Oil in the fuel. The knock went away after a while. I kept using MMO. Later I had the head in to a machine shop and the mechanic commented on how clean the passages were.

I had to use a ridge reamer to remove the carbon ring on cyl to get pistons out on my 66 mustang. Leaded gas. It was not cyl metal wear… Took apart a 68 327 that had a ton of carbon buildup on the valve stems. Cyl were ok.

I don’t know how bad the carbon build-up.is, but I had the detonation (spark knock) on two different cars. The most recent was a 1978 Oldsmobile Cutlass with the 260 V8 engine. About once a month, I would add a can of Casite Motor Tuneup.(not Casite Motor Honey) to a tank of gas, take the car out on the interstate and run it up.to 65 in a lower gear range. The black smoke would roll out of the exhaust. In less than half a mile, I would shift into “D” and the car would be fine. I then heard on Cartalk that certain 10W-40.oils had polymers that could cause carbon build-up. switched to 10W-30 and that cleared up the problem. I didn’t have to give it the Casite treatment after switching to 10W-30. The owner’s manual specified either 10W-30 or 10W,-40. I assumed 10W,-40 was better, but I was wrong. The Oldsmobile never used oil in the 33 years I owned the car, and the switch to 10W-30 didn’t make the car consume oil.
I also had a 1954 Buick with the 264.“nailhead” V8. I gave it the Casite treatment. When I sensed a carbon build-up, I would pour a can of Casite Motor Tune-Up in the gas tank. take it out on the highway and run it up to 65 mph in second gear (it was a manual transmission). I don’t know if Casite Motor Tune-Up exists any more, but there may be something equivalent.

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