February 24, 2017 • Tim Technical Support Specialist

GAS! GAS! GAS!

Welcome to this week’s tech talk at Venom Motor Sports!

Spring is in the air and we are all excited to get out riding again! This time of year I get all kinds of questions about gas and fuel systems, so we are going to take some time to look at a few of the more common questions.

This week’s blog is part of an ongoing series on “Fuel Systems”. I hope you enjoy them.

The fuel systems on our bikes are pretty straight forward. The fuel starts off in the gas tank...then flows through a “pet cock” or shut off to the fuel filter, then from the fuel filter to the carburetor.

Today, we are going to spend some time chatting about the fuel system and various types of fuel available for our bikes.

To help with your understanding of fuel systems please click on the various “fuel system” videos links below. These will help you understand the different components in the fuel system and how they may be serviced.

Thank you “youtube”!

Keep in mind that this information applies to all of our gas powered bikes!

Onto this week’s topic!

Tim...After winter storage I am having difficulty getting my bike to start. What checks should I perform on the fuel system?

Well...the first question is, did you empty out the fuel system before putting your bike away in storage over the winter months?

To drain the fuel tank you need only remove the fuel line at the carburetor and drain out the fuel from the tank. Once the fuel tank is drained, re-attach the fuel line to the carburettor and start the bike. Run the bike and burn off any other fuel still left in the carburetor. When the running bike stalls out...there is no more fuel left in the tanks, fuel lines, shut off valve, fuel filter or carburetor.

Why is this important? As fuel sits it gives off vapors and losses “volatile organic compounds”. This means that the fuel will not be as combustible in 6 months time as it is today. So fresh gas is good gas!

Also as the bike sits in the garage and undergoes temperature change it is possible for various waxes and paraffin’s to drop out of solution and become solids. This is where the term “my carb is all gunked up” came from. Another problem that can occur as gas sits in or bikes is moisture separation. Water will separate from the fuel...and with some oxygen will rust components very well given a chance.

So the best procedure we can follow for our bikes is to drain all fuel before storing them away.

Now, if you feel that is too much work...you can cheat.

The “cheat” is to ad fuel stabilizer to the gas in your tank. The stabilizer helps the fuel retain its “VOC” content and prevents breakdown. So your gas will be fine next spring.

I personally prefer to drain my bike. Never was a good cheater!

Once you have changed or treated the fuel in your gas tanks, check to ensure that the fuel on/off valve is open and that there are no kinks in the fuel line.

Then try to start your bike again.

Tim...How do I know if my “pet cock” or shut off valve is open or closed?

This can be tricky as they are not always clearly marked.

Generally speaking when valve handle is in an up and down vertical position the valve is open. When the handle is horizontal the valve is closed. Second rule of thumb is to ensure that the handle is lined up in the same plane as the fuel lines. If it is, then the valve is open.

You will be able to check this as you will be able to see fuel flowing into the fuel filter.

If your bike will not start...a good place to begin your troubleshooting is with an easy test procedure.

Remove the spark plug and add a few drops of gasoline directly into the cylinder.

Re- install the spark plug and try starting the bike. If the bike starts but then stalls...you have a fuel based issue. Very commonly it is the fuel valve that is not open, or one the fuel lines is kinked or you still have last year’s gas in the tank.

Tim...How often should I change my fuel filter?

The basic rule of thumb I use is everything three years. This works well for bikes driven on the street.

If we are talking about a dirt bike or ATV then to be safe I would change the filter every two years or sooner depending on the condition of the filter. These days most fuel filters come with a clear outer casing, so you can actually see the filter. When the filter media looks dirty, replace it. It’s that simple.

Inside your carburetor you will have too very small ports that the fuel must flow through to mix with combustion air and enter the engine cylinder on the intake stroke.

One is an idle port or jet and the second is the main jet. These have holes which are about the size of a needle or smaller. Needless to say any containment in the fuel will plug these up.

So where does all this dirt in the fuel filter come from?

Some of the dirt came from the gasoline vender and the rest from the environment in which you are driving your bike.

All fuel tanks have air vents...so air is always going to be coming in contact with your gasoline in the tank. The question is...how clean is that air? Any contaminants in the air will find their way to the fuel, then the fuel filter.

Once the flow rate of fuel is reduced to your engine, the engine will perform poorly or “bog” down.

Changing the fuel filter is an easy process as you need only remove and re-attach the fuel inlet and outlet lines

Tim...What the heck is “Octane”? How does “octane” affect the rating of my fuel?

Octane is a gasoline rating system that indicates how much the air/fuel mixture can be compressed in an internal combustion engine before it spontaneously ignites. Octane is an additive to gasoline to resist premature ignition. It does not affect the energy value of the fuel.

You may have heard of the term “engine knock” or “ping” these are terms used to describe the noise produced when your engine is suffering from early detonation.

In a typical gas powered engine the air/fuel mixture enters into the engine cylinder on the intake stroke and is then compressed during the compression stroke. As the name implies the air/fuel mixture is compressed as the piston moves from bottom dead center to top dead center. The greater the volume of air/fuel mixture compressed, the higher the compression ratio of the engine. High Octane levels are really only needed on those engines with a compression ratio higher than 10:1. This means for example that an engine with a compression ratio of 10:1 will compress an air/fuel mixture of 10 cubic centimeters to 1 cubic centimeter in volume.

It is during this compression that the air/fuel mixture heats up due to the heat of compression and residual heat in the engine cylinder walls. If there is too much heat, the air fuel mixture will pre ignite before the spark plug fires and this can cause an unbalanced pressure wave in the cylinder producing unbalanced force on top of the piston. Typically we want the air fuel mixture to ignite just before the piston reaches top dead center of the compression stroke. This is done with the spark plug located right in the middle of the cylinder head and perfect engine timing. This ensures that the fuel ignites evenly and produces a pressure wave evenly across the piston head. However, sometimes while the main fuel ignition is occurring a separate spontaneous pocket of ignition will occur closer to the sides of the cylinder wall.

When the piston is acted on by unbalanced or uneven forces pushing it downward it will be pushed to one side, this is what does the damage to the piston rings, cylinder wall, cylinder head and makes that funny “ping” sound. If your engine ever makes a funny “ping” sound jump up to Octane level 91 right away. Again I have never heard the funny “ping” sound coming from one of our bikes. Typically our smaller bike engines have compression ratio’s in the 8:1 range and work just fine with an Octane level of 85 or 87.

However , if your are driving one of our x19, x20 or x22’s then I would recommend using gas with an Octane level of 91 or 94.

My basic rule of thumb is to always use Octane 91 fuel with any air cooled again.

When choosing a gas station, try to pick one that refills their fuel tanks often. You are looking for the busy gas station...not the one with three customers a day.

This will ensure that you are getting “fresh” gas and I also prefer gasoline’s that have detergents in them to help keep the fuel system clean.

Tim...Is the air vent on top of my fuel tank important? What does it do?

Actually the air vent is critical and very important.

The air vent on your fuel tank allows atmospheric pressure to push down on the fuel in the fuel system and along with gravity get the gas to flow from the tank to the carburetor.

A plugged air vent will reduce the rate of flow of fuel and cause the engine to “bogg” down or stall out.

Tim...Have you found any good video’s on “fuel systems” for our bikes?

Yes! gotta love “youtube”, thank you fellow youtubers for sharing your videos.

The video’s listed below are some of my favorites. Just click on the link below!

What does The Octane Rating Of Gasoline mean?

https://www.youtube.com/watch?v=1ToBZ74Yhas

Fuel Petcock Sillyness

https://www.youtube.com/watch?v=iHQv4QpCVGc

Blocked Fuel Tank Vent On A Dirt Bike

https://www.youtube.com/watch?v=_qUjjQJJTug

How To Fuel A Motorcycle

https://www.youtube.com/watch?v=71WEKMCxuI4