Mistake Lead To Motorcycle Vapor Lock.

Yup, here to confess, I skipped a step in my Boom Vader’s Carburetor Upgrade and managed to cause my motorcycle vapor lock condition.  

Often, power loss after riding these little motorcycles for a while and then disappearing with opening the gas cap is called vapor lock, but that is wrong. I found that this so-called vapor lock condition is a vacuum developing in the motorcycle gas tank, which is relieved by venting the tank. Read more here: Vapor lock.

Even after disproving the motorcycle vapor lock excuses for an unvented gas tank, I got real vapor lock.

What Can Cause A Vapor Lock On A Motorcycle?

Motorcycle vapor lock occurs when liquid fuel isn’t liquid but has flashed to a vapor in the carburetor or fuel line.

Well, I Had A Real Motorcycle Vapor Lock Condition.

While riding my motorcycle, the internal heat of the air-cooled engine is migrating out to the engine cooling fins. All is well as long as air is moving over the fins.

Well, after riding for a while and coming to a stop, the airflow stops, and so does the engine’s air cooling. However, the engine’s heat from the cylinder is still being transferred through the engine’s metal.  

Part of the engine’s metal is the metal intake. With the intake’s position over the engine, heat rising, and heat conduction through the metal, the intake gets hot at these stopped conditions.

Because of my mistake, which I will cover, this heat was transferred to the carburetor. So, while the bike was running great at full speed( Boom Vader 125cc Top Speed ), shortly after stopping, the engine would stumble and lose power, often stalling the engine.

Now, I did not have standstill stalling conditions at the start of my bike, only after riding my motorcycle for a while.

Chasing My Carburetor Gremlins.

I checked and tested and couldn’t figure out why I was losing power, and then I noticed the pattern. I lost power after riding for a while and during periods of standing still afterward. Once the bike was running again and I was moving, the little Boom Vader motorcycle ran like a champ.

I was messing around with fuel/air screws, trying to figure out what size pilot jet I should change to, and even started tweaking my main needle position. I was going to change the carburetor jets on my little bike entirely.

Well, after a long ride, I started examining the carburetor and noticed the engine intake was hot and the carburetor was very warm. Even with the engine off, I smelled a strong gas smell. The heat was being transferred into the carburetor, and gas in the fuel bowl was flashing to vapor. I had a vapor lock.

Once I figured this out, I realized what the extra plastic piece that came with my upgraded Boom Vader’s carburetor kit was for. Originally, I left this small piece out, thinking that it moved the carburetor too far forward, resulting in the air filter touching the forks on turns.  

Because of this simple reason, it was not installed, leading to overheating my carburetor and creating an actual vapor lock condition on my motorcycle.

My Simple Vapor Lock Solution.

Well you guessed it. I found the small non-metallic flange I left out and installed with the non-metallic flange’s o-ring against the metal engine intake and the carburetor’s o-ring against the non-metallic flange.

The non-metallic flange insulated the carburetor from the direct heat transfer from the motorcycle engine’s metal intake.  

My symptoms of a vapor lock stopped.

The lesson learned is that these little upgrade kits we buy online often come with no instructions, but we must assume they are low-priced and sold with minimal parts. This means everything in these motorcycle carburetor upgrade kits has a purpose.

Your Feedback?

Have you had problems with your motorcycle’s vapor lock? Have you felt it with these little Grom-Clone motorcycles? If so, please leave a comment.