HELP: 4-stroke 49cc (142F motor) turns off when choke is open

[MuayThaiJJ]

HELP: I bought a semi-new 4-stroke 49cc (142F motor) bike but it sat for a while unused. It starts fine, but when I move the choke to run (open) position the engine turns off. So it only runs with the choke on start position and has very weak torque. I am pretty sure it's the carb, but am new to this. Any advice? thanks!

 

[ImpulseRocket]

HELP: I bought a semi-new 4-stroke 49cc (142F motor) bike but it sat for a while unused. It starts fine, but when I move the choke to run (open) position the engine turns off. So it only runs with the choke on start position and has very weak torque. I am pretty sure it's the carb, but am new to this. Any advice? thanks!

If it sat with fuel in the carburetor at all it is most likely going to be gummed up. That will explain why it won't run. Pull the carburetor and clean it well. It helps to pull the jets out to make sure you get them clean. If you have an ultrasonic cleaner they can really help with getting the small passages cleared out. Just make sure to blow some air through the various passages too to make sure they are clear. Compressed air is ideal, but even just a "duster" can of air can help.

 

[Gordy]

If it will run without choke in the upper RPM range it's a clogged Idle circuit, if not it's likely a clogged main jet. Either that or you have an air leak somewhere.

 

[Sidewinder Jerry]

Once fixed, to prevent future problems only use a 100% ethanol free gas. Cost a little more but solves 90% of the issues with clogged jets and clogged inlet carburetor fuel screens. These carburetors are very affordable on eBay and Amazon

Change your fuel filter, clean the air filter, and change the oil.

You should also check the valve lashes to make sure they're at the proper setting.

Check the coil to flywheel clearance, and use a spark plug tester to make sure you're getting good spark.

These are just a few standard things to do when buying a used engine with operating issues.

.

 

[MuayThaiJJ]

Will using some fuel treatment help at all if I don't have easy access too 100% ethanol free gas?

 

[ImpulseRocket]

Will using some fuel treatment help at all if I don't have easy access too 100% ethanol free gas?

If you have to use blended fuel the big takeaway is to not let the fuel sit in the system. At a minimum it's a good idea to drain the bowl of the carburetor before letting it sit any longer than a few days.

 

[MuayThaiJJ]

Ok, just curious. I have zero experience with engines. Can I just shoot carb cleaner through the fuel line with the bottom drain open to clear out the gunk? I did do the idle plastic piece cleaning with a thin guitar string, the string didn't go through all the way in the brass hole, was it supposed to? Maybe I need to also use carb cleaner on that small plastic piece?

 

[MuayThaiJJ]

Ok, I just realized the G string from an electric guitar is slightly too thick to go through the hole in the idle jet. I used the next highest string and it was the perfect thickness to go through and clean the idle jet. I have successfully started the 4-stroke and put the choke to run position and the engine did not die. Next step is to try and ride it uphill, it would not do that last time I drove it with the choke in start position.

 

[Sidewinder Jerry]

Will using some fuel treatment help at all if I don't have easy access too 100% ethanol free gas?

Using treatments and not allowing it to sit for long periods of time only delays the enviable. Though it'll take longer eventually ethanol fuel is going to cause carburetor issues.

 

[MuayThaiJJ]

Thanks, I did find an ethanol free gas station not crazy far, I will stock up!