See full version: The Causes of Carbon Fouled Spark Plugs
When a vehicle does not drive for an extended time period, the spark plugs do not get hot and that means they cannot burn off the carbon or fuel deposits. A vehicle left idling for a long period of time will often end up with carbon fouling. When a vehicle is not going to leave soon, turning off the engine will prevent fouling from vehicle idling because it will eliminate carbon deposits. [links]
Stop-and-go traffic, where a vehicle is stopping constantly, is never good for the vehicle. It not only lowers vehicle gas mileage, but it can result in carbon fouling of the spark plugs. Unfortunately, it is impossible to prevent stop-and-go traffic conditions. When a vehicle is constantly in stop-and-go traffic, checking the spark plugs regularly for carbon build up, which is a sooty, black material that builds on the spark plug can prevent damage to the spark plug and allow cleaning before problems start. [links]
Carbon fouling is one of the potential fouling problems that happens to spark plugs. According to NGK Spark Plugs, when the insulator nose of the spark plug is coated, it is considered fouled. The website continues to explain that while carbon fouling can cause problems, if the spark plugs are cleaned, there should not be any problems afterward unless the spark plugs were also damaged.
A rich fuel mixture can result in carbon fouling. There are several potential reasons the fuel mixture is rich and these reasons range from a leaky fuel injector to problems with vehicle oxygen or coolant sensors. The only way to determine if the fuel mixture is too rich is by getting the vehicle checked for problems like sensors that are not working. here
Incorrect jetting is one of the most common causes of plug fouling, but we’ll look at what the top reasons why your dirt bike keeps fouling spark plugs and how you can fix it before spending a ton of cash on continually replacing spark plugs. more
If you have too much oil in the mixture (such as 12:1), then you will probably end up fouling the plug because it is more difficult to burn that much oil. Don’t try to cut corners with the oil though, because it’s very important for your dirt bike’s engine.
The carbon (fuel) eventually builds up on the spark plug so much that it can’t ignite the air-fuel mixture: this is what’s known as a fouled spark plug. more
If the valves are okay, then you should check your compression. Anything between 90 and 120 psi is good. If it's low then you probably need new rings. The rings could have went bad from the running with no oil, the con rod and it shakin all around in the chamber. This could cause smoke as well. here
Change the spark plug. Ensure it is the correctg plug and the Heat Range. Possible it is getting grounded out internally. A new plug may solve the problem.
Oil and fuel fouling can both cause condition known as bridged gap, where carbon or oil deposits build up in gap until gap completely blocked.
I found this mentioned on a website, I know it is lengthy but good informaion:
If the spark plugs are worn or dirty, it my take a lot of energy to spark the plugs and ignite the fuel. The engine is also cold making starting a little harder than if it was up to operating temperature.
The last sign that you have bad spark plugs is that the engine is hard to start. Now there are other causes for hard starting vehicles, for instance if you have a carbureted motorcycle check out our article here on why they can be hard to start. However, spark plugs can be the cause of a hard start.
Spark plug life can vary drastically by the material used. Copper plugs will be good for 10,000 to 20,000 miles, while platinum or iridium plugs can be good for 60,000 miles or more. In motorcycles, plugs typically only last 15,000 miles, while car and truck spark plugs can last from 30,000 miles to even 100,000 miles.
Check engine lights will trigger a certain code. Be sure to check this code and determine what it means. A P0300 code indicates a cylinder misfire and can be related to the spark plugs, while a P0171 would be related to PCV valve issues. more
As you can see the replacement intervals can vary by 70,000 miles in different applications. Its very important that you look at your specific vehicle and see what interval the manufacturer recommends.
In a four stroke engine, a spark plug will ignite every four revolutions. Since a motorcycles regularly operate at 8,000 rpm or higher, the spark plug is igniting 2,000 times per minute. Whereas a car usually operates in the 2,000 – 3,000 rpm giving 500 to 750 spark plug ignitions per minute.
Please can someone offer knowledgeable advice?
It has never been a smooth runner, but was ok until recently when a Thai "helper" ran it with no oil, resulting in a broken con-rod. This was repaired by local motorcycle mechanics. Then because it died completely another repairer serviced the carburetor and installed a new diaphragm. It appeared to run ok.
Deposits caused by fuel and oil fouling can usually be cleaned from plug and plug reinstalled in engine. However, since plugs inexpensive, should usually simply be replaced during tune up.