My Te450 Bogs If I Give It A Quick Twist On The Throttle, From Idling.

Hi.
My TE450 ('07 EURO3) don't respond as quick as I want to, and sometimes bogs if I give it a quick twist on the throttle when it idles. When I start it, cold, with the electric starter, it sometimes backfires and it feels like it almost stops. Is my ignition "too early" maybe?

dirty air filter or rag in the intake?
vacuum leak? (or cracked manifold)
spark plug?
electrical issue in the secondary? (plug cap, moisture, plug wire)
electrical issue in the primary? (broken or lose wire, bad connection, bad coil)
compression leak? (valves, head or gasket if you're consuming coolant)
[inspect & clean carb for these next few:]
accelerator pump?
pilot jet?
float level low?
choke?
bad/old gas?

I doubt the timing has changed... but it could be a bad pick-up coil.

I know that I've thrown a lot of probabilities around, but it's a fairly non-specific issue.

one of our mods has an '07 TE450... maybe she has some advice.
post a video if you can.

let me know if there is too much idiomatic americanisms in there.

good luck.

Thanks!
I guess I'll have to start with the carb, and pick it down, and clean and look it over. I've just totally rebuildt the engine, but the respond was like that before I did that too. When I rebuilded it, I had to replace the rubber intake. The original one, has a hose-connection on it, for a hose to a solenoid(?)-sensor or something. I could'nt find that part new, so I had to leave that uninstalled. But I've read that this would not be a problem.
It's a lot of shit on these Euro3 bikes. I know it can be removed by a race harness or something like that, but I like the key ignition, and the fan.

This sounds similar to my issues. And my recent post. 2010 TE250 Engine won't stay running.

2010 TE450, I went thru 3-4 intake boots...