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I’m all choked up! - How to use the choke on your new bike - cold start

Posted by Tim Technical Support Specialist on

I’m all choked up!

Welcome to this week’s tech talk at Venom Motorsports!

The “choke” function on our bikes can sometimes be a little tricky to get the hang of.

This week we are going to chat in very practical terms how to use your choke...and the problems you may have experience with it. We will also demonstrate choke operation in our youtube video link.

Keep in mind that this information applies to all of our fine gas powered Super Pocket Bikes, Dirt Bikes and ATVs!

Ok onto this week’s topic.

So Tim...How does the choke work? LOL a little theory first!

The purpose of the “choke” is to enrich the air fuel mixture to help start a cold engine. Cold is the key word here because a “cold engine” will not easily vaporize the fuel in the air fuel mixture entering the engine. So we need to enrich the mixture in a cold engine to increase the amount of combustible vapour present.

When you close the “choke” you reduce the volume of combustion air entering the cylinder, this changes the air/fuel ratio to a very rich mixture. More fuel in the air fuel mixture than normal helps the bike to achieve ignition of the air fuel mixture and start.

Let’s review the combustion KABOOM equation.

Spark + Fuel + Air = KABOOM!

When KABOOM occurs the piston is pushed downward in the engine cylinder, which turns the crankshaft, which turns the gears in the transmission, which drives the chain, which turns the rear wheel gear, which makes you go zoom! So KABOOM is most important.

When discussing the air/fuel mixture in the engine, the key concept is the ratio of fuel to air. For all fuels there is an upper and lower air fuel ratio that will support combustion. If your too rich...no kaboom, if your too lean...no kaboom. It needs to be just right to get the best performance out of your engine.

Tim,...When is the “choke” on? And what the heck does that mean?

Inside the carburetor is a choke plate. This is a movable plate that opens and closes allowing more airflow through the carb or less. When the choke is engaged, the choke plate covers some of the carb throat opening. We would say that the “choke” is on or closed. This restriction of air flow reduces the amount of air available for combustion which means that the air fuel mixture is very rich. A rich mixture is needed to start your bike when it is cold...colder than a cup of coffee.

Typically the “choke” is on when the choke lever is in the up position or when the choke lever is inline with the handle bars on your bike. Choke on means that the choke plate is covering the carb throat.

The “choke” is off when the choke lever is down or when the choke lever is facing you if your choke is a handle bar mount. Choke off means that the choke plate is not covering the carb throat.

Tim...Ok so its a warm day and this is the first time starting my brand new bike. I gave the bike full choke and I tried and tried but it will not start. What’s wrong?

We only need to “choke” a bike when the engine is cold...that is to say not as warm as a cup of coffee.

If the bike is warmer than a cup of coffee no choke is needed.

The above condition occurs when you choke a bike when it does not need it. The bike will become flooded and not start. To get it going, simply open the choke...or think of it as NO choke. Give the bike some throttle, say ½ open throttle and try to start the bike. The ½ open throttle will help bring more air into the cylinder allowing the air fuel mixture to ignite. Once the bike starts release the throttle and allow the bike to warm up before driving away. Say 30 seconds to a minute at idle to allow lubricating oil in the engine to reach every part of the engine. Always a good rule of thumb.

 

Tim...Ok so its a cold morning and this is the first time starting my brand new bike. What do I do?

This is a great question again the key word is “cold”.

If the bike is cold than yes! Close the choke fully before trying to start it, and do not touch the throttle. Once the bike starts and warms for a minute you can open the choke and drive away. This is a good practise as all bikes need to sit for that first minute of operation to allow for lubricating oil to work its way through the engine. Just giving your bike a minute to warm up will extend the life of the engine. I know its tuff to do because we all want to just take right off...but it’s a good habit to form.

Ok so if the bike has been sitting in the sun all day...do I still need to “choke” it to get it started? No choke is needed. If the engine is warm, the engine will start right up.

What if I was riding the bike, than stopped for awhile? Do I need to “choke” it again to get it started? Again No... If the engine is warm, the engine will start right up.

Ok Tim so how warm is warm enough? Think about a cup of coffee in your hands, yeah about that warm is warm enough to not require any “choke”, LOL but warm enough to require a warning label on a cup of coffee.

 

hTim...I have a very hard time starting my cold bike. It seems that I have to roll my bike over many many times to get it to start, once it starts it seems to run perfectly, what’s the problem?

This was a customers question that I have delt with a few times. Can you guess what the problem is? This person never read any of my blogs or even the starting instructions for his bike. He did not know what a choke was...and simply rolled the bike over enough times to warm up the cylinder to the point where the air fuel mixture would ignite.

I was on the phone with him...as he was trying to start his cold bike. I explained to him what the choke did and how to turn it on. Before rolling the bike engine over, I got him to choke the bike and it started right away! He was amazed!!!

This has happened to me more than once. The choke really is so very important for cold starts.

Tim...What can I do if I am really not sure if the choke is open or closed?

If you are not sure if the “choke” lever is in the open or closed position you can figure this out easily.

Simply remove the air filter fitted to the carburetor and look into the throat of the carb.

Move the “choke” lever back and forth.

When the “choke” is closed you will see a metal plate restrict the opening of the carb throat. This is the CHOKE ON! position.

When the “choke” is open you will not see the metal plate and you can see right into the throat of the carb. This is the CHOKE OFF position.

Tim...what happens if I drive the bike with the “choke” closed?

Well this is something we have all done at some point.

As the engine is running very rich it will tend to “bog” down when you hit the throttle.

So when you give the engine throttle to speed up...it will do so very slowly, seem to have no power or simply stall out as the air/fuel mixture is too rich.

No need to worry, once you open the “choke” up your bike once again runs just fine.

Tim...I have heard of “flooding” the engine, what does that mean?

Flooding the engine happens when you “choke” an engine that does not need to be “choked”. With the “choke” closed we roll the engine over again and again and again without achieving ignition of the too rich air fuel mixture. This floods the cylinder with a super rich air fuel which will not ignite or support combustion as there is too little air in the air/fuel mixture. No need to worry, just open the “choke” give the engine ½ throttle and try to start the engine again. If you are feeling handy pull the spark plug, clean it than open the engine throttle full wide open. Role the engine over a few times to purge the cylinder. Once purge reinstall the spark plug and your engine should now start up, no problem.  

My only concern here is with a “super choked” engine. Where the engine was rolled over multiple times, should have started but did not. This condition can cause some gasoline to make its way into your Lubricating oil and ruin it. When does this happen? Well typically its the spark plug, not the choke that is the problem. Before going into intense trouble shooting simply replace the spark plug. Spark plugs are a $3.00 part that can save a lot of frustration. If in doubt chuck the plug out! If you know that you “super flooded” the engine it is a wise move to change the oil before starting it again.

I hope you enjoyed this week’s tech talk, please take a moment and check out our “I’m all choked up” video on youtube!

If you have any tech questions about our bikes, please feel free to email them to...

Support@venommotorsportscanada.com

Have a great day!

Tim

Technical Support Specialist

Venom Motorsports Canada

 


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