How to troubleshoot vacuum lock problems
This is a simple guide to engine fuel mixture problems due to fuel tank vacuum lock. Vacuum lock occurs with the China Girl engine kits due to having too good of a seal on the tank gas cap. These caps are designed to vent fuel vapor when the air inside the tank expands, however they often fail to vent properly causing poor performance, lean out conditions, and engine stumbling due to fuel starvation in the float bowl.
Vacuum lock is a simple condition caused by the air trapped inside the fuel tank lowering in pressure from when the last time you put gas inside the tank and having a cap that does not vent. It is most common in cold conditions, and dramatic downward temperature changes. It also happens when you go from a full tank to an empty tank with a tight cap seal. During warm weather and stable air conditions, this should not be a problem. However, riding from a high to low altitude can also cause this, although I have no first hand experience with it due to my local geography.
The good news is it is a very simple fix. First though I want to discuss what symptoms you should look for. If you are sure of these following factors, and you have no other fuel problems with your engine, then you should pursue the solution to vacuum lock, which is simply opening the gas cap on your tank and closing it again, equalizing pressure. Here is what to look for first in ensuring you aren't having other conditions mimicking vacuum lock. Fuel leakage from the fuel line causing low fuel level is something that will cause similar symptoms. If the fuel line around the fittings are dry and not wet and you do not see fuel pooling underneath the carb, then this is not your problem. If you use the 'tickler' device which taps on the float to get it unstuck, and this does not alleviate your problem, then you know it could be vacuum lock. If your filters are clean and you have checked them, then it most probably is vacuum lock. Lastly, make sure the fuel shut off valve is open. Definitely this will make your engine lean out just like vacuum lock will. Now if all these other things have not solved the problem, open that gas cap and purge the air and reseal it. Give the fuel 15 seconds to fill the bowl back up and it should start right up. Oh, and one more thing; check the choke setting often and know which way is closed and which way is open. If the motor is warm, it should always be open. It only takes less than 30 seconds for the engine to warm sufficiently to open the choke.
Have fun riding.
This is a simple guide to engine fuel mixture problems due to fuel tank vacuum lock. Vacuum lock occurs with the China Girl engine kits due to having too good of a seal on the tank gas cap. These caps are designed to vent fuel vapor when the air inside the tank expands, however they often fail to vent properly causing poor performance, lean out conditions, and engine stumbling due to fuel starvation in the float bowl.
Vacuum lock is a simple condition caused by the air trapped inside the fuel tank lowering in pressure from when the last time you put gas inside the tank and having a cap that does not vent. It is most common in cold conditions, and dramatic downward temperature changes. It also happens when you go from a full tank to an empty tank with a tight cap seal. During warm weather and stable air conditions, this should not be a problem. However, riding from a high to low altitude can also cause this, although I have no first hand experience with it due to my local geography.
The good news is it is a very simple fix. First though I want to discuss what symptoms you should look for. If you are sure of these following factors, and you have no other fuel problems with your engine, then you should pursue the solution to vacuum lock, which is simply opening the gas cap on your tank and closing it again, equalizing pressure. Here is what to look for first in ensuring you aren't having other conditions mimicking vacuum lock. Fuel leakage from the fuel line causing low fuel level is something that will cause similar symptoms. If the fuel line around the fittings are dry and not wet and you do not see fuel pooling underneath the carb, then this is not your problem. If you use the 'tickler' device which taps on the float to get it unstuck, and this does not alleviate your problem, then you know it could be vacuum lock. If your filters are clean and you have checked them, then it most probably is vacuum lock. Lastly, make sure the fuel shut off valve is open. Definitely this will make your engine lean out just like vacuum lock will. Now if all these other things have not solved the problem, open that gas cap and purge the air and reseal it. Give the fuel 15 seconds to fill the bowl back up and it should start right up. Oh, and one more thing; check the choke setting often and know which way is closed and which way is open. If the motor is warm, it should always be open. It only takes less than 30 seconds for the engine to warm sufficiently to open the choke.
Have fun riding.
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