Purchased a 67 326ci last fall, found the vacuum advance disconected and I now beleive the heads and values are carboned up. My questions are:

1. Will Sea Foam down the carb clean the carbon or is Sea Foam snake oil?

2. Pros and Cons

3. Other sugestions on removing the carbon without tearing the heads off?

What makes you think it's carboned up? Tune it, make sure you have the appropriate octane fuel for your engine and run it a little hard. It should burn off.

I have done a complete tune-up, set the timing correctly, curved the distrbutor and still get a rattle at cruise rpm and light thottle using 93 octane. I believe that the previous owner drove around with the vacuum advanve disconected which is ok if your drag racing but will carbon up the top half on the street. I think my rattle is the carbon deposits that have collected in the cylinder causing a mild knock at cruise. The engine does not use any oil but the exhaust pipes are carbon black. I disconnect the vacuum advance the rattle goes away, but it loads up the plugs if driving with light thottle after a few hundred miles. I think I'm on the right track with the carbon deposits, just not comfortabe dumping somthing down the carb that I'm not familiar with. I'm looking for someone who may have used Sea Foam and can commet on the product.

If your engine is stock compression it will rattle with 93 octane. They all do. The previous owner probably unhooked the vacuum advance to help curb the spark knock(rattle). Try to mix in some racing fuel and I bet your spark knock goes away. If you burn 93 long enough the rattle may become permanent. The spark knock can break out the lands between the rings and it sounds like spark knock when it rattles. If your plugs are fouling without oil usage it's most likely a carb problem.

The carbon is from lack of advance.

If it's a 326 4 bbl, with small chamber 326 4 bbl heads, mix 110 octane 50-50 with 93 and drive with vacuum advance connected at cruising speeds for several miles, then recheck plugs.

If you see an improvement in rattle and plug condition, you need higher octane. My '69 400 is the same.

If you still have rattle but clean plugs, check your distributor advance curve.

If you still have rattle and dirty plugs, check your carburetor's cruise metering and overall condition.

If you have 2bbl heads or other low compression heads, you shouldn't rattle.

Yellowbird I agree with you. I failed to mention that it is the 2 bbl 326 9.2:1 low compression engine. 93 octane is the highest octane pump gas you can get, I should be able to run on 87. I believe it's the carbon built in the heads which has raised the compression some. Once again I'm looking for input on the Seafoam treatment for clearing carbon. Someone out there must have expermented with it, it's been around since the 40,s. If I chemically can't clear the carbon I'll pull the heads.

If you really want to clean the carbon out of your engine follow these simple steps. Fill an empty soda bottle with water. Remove your air cleaner. Start your engine. While using one hand to control the throttle, trickle the water into the carb or throttle body with the other while holding your thumb over the bottle opening. Keep the engine rpm's up so that the engine doesn't die. Make sure that you don't pour the water in too fast! Water doesn't compress and if you pour too much water in, severe engine damage can result! White smoke from the exhaust is normal.
Try it and report back how it works for you.....

Have also use water, but in spray bottle to atomize the water some before going into the carb. It works.

sounds like something other then carbon. 9.2 should work well with pump gas. if he raced it could be internal like bearings.

Try cooler spark plugs. Plugs with very deep wells around the center electrode hold a lot of heat that can result in preignition. Cooler plugs have a shallower well and don't hold as much heat in the combustion chamber. I've got a 350 with #16 heads that have been milled to 69cc's. I run 93 octane pump gas and occasionally throw in a bottle of cheap octane booster if I hear a little pinging.

I agree with you that carbon buildup can create hot spots as well. Try the water first - with an atomizer.

To comment on the Sea Foam issue. My car has a lifter tapping. The previous owner said he put Sea Foam in the engine to try to eliminate the problem. He said as he drove the car, the tapping started to dwindle. I change the oil when I bought the car, therefore getting rid of the Sea Foam. The lifter still taps. I don't hold too much light to the stuff.