Can you recomend a cleaner i can add to the gas tank to clean fuel system on a craftsman 25-cc trimmer

Look for air leaks in the gas line and around the carb , a bad gas cap will not let any pressure build up. It could be that too. Check also the fuel line and filter inside the tank. replace if needed.
www.ereplacementparts.com has parts for craftsman or the online Sears Stores.

Hi There, Check the primer bulb for tare or pin holes. Replace it. Check and clean carb jet it maybe plugged with debree. Also check for spark which you didn't say. Replace with correct plug.
Note; Do not use strong cleaners on rubber seals (O rings and gaskets) They dry up and crack.
If needed use a dabble of grease on seals

the other possibilities you have is a bad crank seal, or a flywheel came loose and its out of time, will it fire on carb cleaner sprayed in the carb, If it runs for seconds and , then I would say it's not getting fuel, If it only farts once or twice then I would check crank seals cause if they are leaking then your crankcase cannot draw vacumn which in turn causes fuel pump in carb to draw fuel, If you have to check flywheel pull it apart and take flywheel nut off and pull flywheel off and inspect the key that is built into flywheel to see if it is sheared off or messed up, also while checking muffler check for the opening that the mud dobbers havent put mud in muffler pipe, good luck

4 oz of a generic 2-cycle oil to a gallon of fuel is the typical mix.

I hope this helps.

Air fuel mixture problem,,,you need to have the filter pulled out and cleaned. Check fuel system for debris and clean, that includes all the fuel lines and possibly disassemble carb and clean and reassemble.

Pull the spark plug,
Squirt a little creeper oil (WD40, 3-in-1, etc.) into the chamber, let sit for a few minutes, and (without the plug) try a few gentle pulls to free up the stuck rings.
Once they move, even a little, tip the head over to drain the oil and add a few drops of mixed gas before replacing the plug.

Replace the gas with mix, and add a tablespoon of Marvel Mystery oil* to the tank...Crank it a few times to get the cylinder free.

* Love this stuff...It will finish cleaning the cylinder and ports, and it's the best deal in fuel system cleaners.

***Don't forget to VOTE for the guys who take an interest in helping!

You shouldn't notice a difference if you remove the air filter. So I would replace it. Also if you are using compressed air to clean or blow-out the carb. Be careful, its not recommended and could make it worse.

try and adjust the fuel/oil mis screws

Probably fuel line into tank has hole in it, If over 5 years old these fuel lines become brittle and break easy. Go to local hardware or repair shop that has small engine parts and you should find the fuel lines. Be sure to take sample with you as there are many sizes. If you have trouble installing them get back to me. Be sure you know how the lines are routed before removing.

its your flaot in your little carb