There are many possible reasons for this happening. The following popular issues are only for reference and may not be the cause. Please directly consult a professional or a Flame Tech representative for an in-depth investigation.
Improperly Sized Cutting Tip/Torch
Using a cutting tip that is too small of a size for your torch or metal thickness will definitely decrease efficiency.
How so? Imagine your torch is a lumberjack cutting down a large tree. Would you ask this lumberjack to do that job with a pocket knife? Of course not! Give that lumberjack a proper axe! Give your torch the proper size cutting tip for the job!
Same problem if your torch is not rated for the job, even though the tip is. The combination will just not work out. There will not be enough gas flow to create the correct preheat and cutting stinger.
If you are cutting metal that is 14 inches thick, you need to use a torch that is rated for 14 inches or better AND a tip that is rated for 14 inches or better.
Hose Is Too Small
Sufficient gas flow is necessary in all parts the equipment. Not just your torch and tip need to be properly sized for the job, your hose needs to be able to supply the proper amount of gas and oxygen for the torch and tip to work as intended. This is a particularly bad situation, because the gas could end up back flowing and burn up the tip, the torch and/or the operator!
Gas Volume Is Insufficient
Same as the hose problem, your equipment needs to supply enough gas for the job. If you are cutting particularly thick metal, your gas and oxygen requirements may be so high that you might need a manifold with an array of cylinders. Consult professional assistance, if you think this may be for you.
Trying to save a buck by using underpowered equipment will only end up costing more in the long run from extending the amount of labor necessary to get the job done. Worse yet, someone could get injured!