put 2-3 oz. of seafoam in gas tank; now won't start/dies

[gstam4]

hey all, i've got a 2001 gz250 w/ 23k miles, bought about two months ago as my first bike.

dealer i bought it from replaced the clutch cable, i think (or was it the choke?), after i was complaining about the bike wanting to die at lights. it was decent after that, but still 'jerky' pretty often; it's like, when i'm cruising in any gear, there's always this point on the throttle that, if i cross it rolling on or off the throttle, the bike jerks and feels uneasy. it's subtle, but a bit disconcerting, especially when i'm rolling on the throttle during a turn.

mechanic at the dealer told me the carb is easy to clean, so that i really didn't need to use seafoam in the gas tank; he did tell me to use non-ethanol, which i've been doing (and also added an inline fuel filter for me). nonetheless, i read about peoples' experiences with seafoam in their bikes, and thought it was worth a try to see if it helped with the jerkiness.

two days ago, i *thought* i filled the tank with gas (see below), then added a small amount of seafoam that couldn't have been more than 2-3 ounces. rode around a little that same day and it was fine. yesterday and today, it's a massive struggle to get the bike started (was worried i was going to burn out the starter), and i need to set the choke near max to keep the bike from dying as i ride around.

could it be that, even though i have an inline fuel filter, the seafoam broke up some gunk in the gas tank or elsewhere, which is now blocking something? any other ideas?

about the gas tank: i thought this was a 2-3 gallon tank, and since i got it have been confused about how quickly i'm going through gas; figured the bike's just old and not getting good mileage anymore. i thought i filled it two days ago, but today when i looked in the tank, it was low enough that i could see some of the bottom of the tank (toward the front). when i fill it at the pump, i keep going until it gets close to the top of the gas tank; i don't wait to see if the level drops if i wait without continuing to fill it (that is, if it takes a few seconds for it to fill somewhere other than the tank?), so is that a possibility? i've gone about 20 miles since i 'filled' it two days ago; there's no way it could have used that much gas, and i don't think there's a leak.

appreciate anyone's advice.