Iplayfarmer- all of these suggestions are valid, but I would still go on the assumption (I know, that can be dangerous..
) that you're not getting fuel delivery from the carb, but other things are OK.
Go ahead & try a new plug; can't hurt. As you say it runs when "primed" I wouldn't worry about the muffler yet, but it's true they will clog up.
I'm guessing you have one of those small Walbro carbs and you put in a carb kit- did the kit come with a diaphragm?
It sounds like your fuel line TO the carb is OK, as you indicate fuel will flow out when it's disconnected.
If it can't get fuel from the carb, which is what sounds like is going on, there are a few possibilities:
1. The diaphragm uses the pulsing pressure in the crankcase to flex back & forth and "pump" fuel through a checkvalve. If the diaphragm has a hole, or is not seated/sealed properly, it won't funtion correctly. There is also that "bleed port", an opening into the crankcase area behind the carb to expose the diaphragm to CC pressures. Also, the carb gasket needs to have a good seal.
2. The cyclical pressure in the crankcase is caused by the movement of the piston up & down, creating both a negative and a positive pressure in the crankcase, alternating between the two. Piston coming down (power stroke)= CC positive pressure, going up (compression)= negative. If there is a compromise in crankcase seals, you won't get the necessary pressure differentials to operate the diaphragm, and if the negative pressure isn't strong enough, it won't pull fuel & air in through the reed valve. But again, as it DOES run --as long as it has fuel-- I'd be betting the reed valve's most likely OK.
The bottom crankshaft seal is usually the culprit, but there are a couple of other seals as well; you'd have to take it apart to see for sure. As far as the reed valve, if it looks OK and seems to seal (can you blow through it backwards?) it's probably OK. Look for burning, cracking, or coking.
3. Any compromise in the seals/gaskets can be a problem... suggestions about the primer bulb, if it has one, are good.
As your machine will run when primed, I think you've already eliminated a lot of other stuff....
Sorry this was somewhat rambling! Keep looking for why the carb isn't delivering fuel.
) that you're not getting fuel delivery from the carb, but other things are OK.Go ahead & try a new plug; can't hurt. As you say it runs when "primed" I wouldn't worry about the muffler yet, but it's true they will clog up.
I'm guessing you have one of those small Walbro carbs and you put in a carb kit- did the kit come with a diaphragm?
It sounds like your fuel line TO the carb is OK, as you indicate fuel will flow out when it's disconnected.
If it can't get fuel from the carb, which is what sounds like is going on, there are a few possibilities:
1. The diaphragm uses the pulsing pressure in the crankcase to flex back & forth and "pump" fuel through a checkvalve. If the diaphragm has a hole, or is not seated/sealed properly, it won't funtion correctly. There is also that "bleed port", an opening into the crankcase area behind the carb to expose the diaphragm to CC pressures. Also, the carb gasket needs to have a good seal.
2. The cyclical pressure in the crankcase is caused by the movement of the piston up & down, creating both a negative and a positive pressure in the crankcase, alternating between the two. Piston coming down (power stroke)= CC positive pressure, going up (compression)= negative. If there is a compromise in crankcase seals, you won't get the necessary pressure differentials to operate the diaphragm, and if the negative pressure isn't strong enough, it won't pull fuel & air in through the reed valve. But again, as it DOES run --as long as it has fuel-- I'd be betting the reed valve's most likely OK.
The bottom crankshaft seal is usually the culprit, but there are a couple of other seals as well; you'd have to take it apart to see for sure. As far as the reed valve, if it looks OK and seems to seal (can you blow through it backwards?) it's probably OK. Look for burning, cracking, or coking.
3. Any compromise in the seals/gaskets can be a problem... suggestions about the primer bulb, if it has one, are good.
As your machine will run when primed, I think you've already eliminated a lot of other stuff....
Sorry this was somewhat rambling! Keep looking for why the carb isn't delivering fuel.
