Questioni have a 19 hp sears tractor that is not getting any gas at carb. i can pour gas directly in top of carb and it will run i have changed fuel filter. change gas with fresh gas checked firing and it is firing. my question is how does gas get from the tank to the carb. i found what looks like a diafram on the front of the carb where the fuel comes into it. took apart and clean but looks good. the fact that it runs when you pour fuel in the carb tells me that everything else is working good, it is just not getting fuel to the carb. thanks for any help you can provide.
AnswerTony
Determining why it won't start
Think: FAST - Fuel, Air, Spark, Timing. Diagnosing a balky engine is not difficult but a step-by-step methodical procedure will make it a lot less traumatic. Despite all the warnings, serious problems rarely develop on their own. Most likely, there is a simple, easily remedied cause.
Fuel
Obviously, the engine won't run without gas!
* Is there some in the fuel tank? If it is near the bottom, add enough so that there is no doubt about there being enough to reach the outlet pipe regardless of any slant on which the lawn mower is located.
* Make sure any shutoff valve is open.
* Check for a clogged fuel filter, if there is one. There may be a sediment catching screen at the bottom of the tank as well.
* If your engine uses a primer bulb, does it feel like it is doing something? There is a distinctly different feel when it is actually squirting a little gas into the intake pipe. Check that the rubber hasn't deteriorated but if many pushes still doesn't do anything (and you're sure there is gas in the tank and the engine hasn't flooded from TOO MUCH gas), the carburetor and/or fuel line may need cleaning.
* If you are using gas from last season, discard it and start fresh. While old gas will usually work in an engine in good condition, this is not always the case, especially with one that has seen better days. The more volatile fractions evaporate leaving behind higher flash point gas. Why add another unknown factor to the puzzle?
* There may be water in the gas. If the carburetor has a drain plug, operate it to rid it of the bottom layer which would have the water. If there is no drain, repeated pulling on the starter cord should eventually clear any reasonable amount of water.
Once you have exhausted these obvious problems, determine if gas is reaching the cylinder as follows: Perform the normal starting sequence and then, assuming it shows no signs of wanting to start, immediately remove the spark plug. If fuel is reaching the cylinder, the spark plug should be damp with gas and there should be a very distinct odor of gas from the spark plug hole. If there is none, then there could still be a blockage in the fuel line or the carburetor may need cleaning.
