Lack of starting power

I am going to guess that the two are not related. The smell might be related to a starter problem and the vehicle might use a little bit of oil. Have you check starter relay and the cabling from the battery?

If you suspect any internal problems, I would suggest pulling out each plug and looking at the tips of them. Note if they are burning black, black and sooty, gray, etc. I would based on those results and possibly anyway, perform a compression check on the cylinders. You would like all of the compression readings to be similar.

Is there any oil usage by the vehicle?
Is there any extra noise from the engine?

Well, when you say one seems not to be burning at all, I would assume that it is not black and oily but maybe a little black and sooty. If the tips are oily and you are puffing blue smoke, the oil useage must be pretty significant. Maybe a quart of oil per tank full or every 500 miles or less?

If the above is true. Let's skip the compression check and go straight to the overhaul section of the book.

You really never said the age of the car and mileage.

I doubt it. The vehicle would be running rough with the drag of the dead cylinder and the power would drop significantly. Take one of the old plugs and connect one at a time to each plug wire. Touch the tip to ground and have the engine cranked over a couple of times. Observe the spark at each cylinder. Is there fire? The spark should be a nice blue arc. If one of the cylinders does not get the spark you need to look at the distributor cap and check the contacts underneath. The wire is probably bad.

Also, excessive black indicates that the vehicle is burning too much fuel. A rich condition. I would check the engine timing.

Compression checking is really easy and the cheapest way might be to either borrow a tester or buy one. They make a wide variety of testing gauges. Most screw into the threads of the plug and some others use a rubber gasket that you hold against the plug hole to seal the plug hole. They all work.