On newer equipment it is often better to just pay the $20 for a cheap carburetor and slap it on. It was likely cheap junk to begin with. In the case of the Jiffy model 30, and I'm sure it depends on how old, they have decent carburetors. Who knows if those Chineese knockoffs are even adjustable, and while most of them work, a scary number are junk right out of the box. I've replaced the carb on my Eskimo Mako, and the first one was bad out of the box. It happens all the time. Buying dirt cheap Chineese carburetors is a crap shoot
The key though is doing an actual carburetor rebuild. I see so many people, especially older guys who half take them apart, leave them in one of those carb dip cans over night, put them together and they don't work. Carb dips might have been an option in the past, but they haven't sold real dip cleaner in a long time now. Those Berrymans paint can cleaners? Scam 100%, don't clean anything except your wallet. You can sometimes get away with nothing but a mechanical cleaning with some needles, aerosol carb cleaner, and an air nozzle, but not always. B12 Chemtool is one of the strongest cleaners you can get today, but when all else fails you really need an ultrasonic cleaner to get these small carburetors fully cleaned sometimes. The other thing is you can't skimp on taking these apart. You absolutely need to remove welch plugs and any plastic caps. Your adjustment screws and jets (jets aren't removable on a Jiffy model 30) need to be taken out. Done right, you will guarantee it will work. Some people don't want to spend the hour it takes to do this though, and may not want to buy an ultrasonic cleaner, or maybe just don't like working on things.