There's an epidemic problem with fuel these days, and many blame ethanol and winterized fuels as the culprit. Whether ethanol or MTBE is the issue, carburetor and EFI system clogging is rampant, especially in vehicles that set for long periods of time.
This became clear when our XR350R Honda dirt motorcycle set for over a year with fuel in the carburetor bowls. This four-valve thumper uses two carburetors, and one has the idle circuit and a pilot jet. The engine ran flawless until parked, then would not idle after setting for a long time.
Most of us are aware of this plague, especially owners of Jeep 4x4s, rock crawlers and OHVs that park for long periods. Essentially, gasoline and diesel fuel has a shelf life. These fuels break down over time. The result can be an inability to fire, severe engine ping and symptoms similar to extremely low octane performance.
In the day, this would simply cause poor performance. A fresh tank of fuel would solve the problem. Remember that old barn find MB Jeep or Bultaco motorcycle that would not start? A fresh tank of fuel (pre-mix for the Bultaco, please), priming the carburetor, and the engine fired! Sure, the carburetor gaskets may have shrunk and they leak now, but we're running!
Today's ethanol behaves like alcohol and bonds with any water in the fuel. This water, instead of laying low in the fuel tank, moves through the fuel supply system. Fuel filter materials, especially pleated paper, swell in the presence of water. This swelling serves as a safeguard to protect fuel injection and carburetor components: The filter clogs and stops fuel flow.
Note: This can even happen from one bad tank of fuel (too much water content). We've all heard about or experienced the gas station that ran its storage tank to the bottom, where the water accumulates. The unlucky customers who pumped that gas wound up with clogged fuel filters.
Back to the XR350R example, the stale pump gas in the fuel bowl and pilot jet caused such severe clogging of the jet that the jet could not be cleaned with carburetor cleaner! (Drilling a carburetor jet is a lost cause; the bit, even turned with finger tips, will scarf into the brass and increase the jet's bore size!) I replaced the jet with the proper size pilot and rebuilt both carburetors. The engine's dependability and performance immediately returned.
So, if your 4x4, OHV, ATV or dirt motorcycle sets up for long periods, consider using a fuel stabilizer or other additives that will prevent fuel breakdown and damage from stagnant fuel. In the case of motorcycles and ATVs with petcocks, always turn off the fuel for both safety reasons and to stop flow to the carburetor. Drain the carburetor bowl(s) when your OHV or bike will set for long periods; most OHV carburetors have a simple drain plug on the bottom of the carburetor's float bowl. Don't overlook the "fuel station" on your toy hauler trailer, either! Use up that fuel or stabilize it.
I keep stored fuel for no more than four or five months these days. If my 4-stroke motorcycle fuel can is setting that long with fuel, the fuel gets dumped into the street/trail driven XJ Cherokee and burned up.
We do the same with the Ram/Cummins diesel and its 75-gallon auxiliary fuel tank. After 60-days without a lot of driving, I will run both tanks down completely, timing the refill for a period when fuel prices will not be devastating: This is a 110 gallon refill, and the 30-50 cents a gallon "futures-based" price hike can be costly.
Does anyone have a gasoline or diesel fuel stabilizer that they find useful and effective? Please share...