Sputtering

My little 1.6L and I were coming home tonight from my brother's house, and it is pretty darn cold, nearing the end of winter, and about 1/2 to full throttle it was sputtering/not accelerating, like it had a rev limiter. What causes this? I'm assuming it is lean or spark is too, or not enough advanced?

I know it's a teeny little motor, but it was even less powerful than usual. Once it got over 3200rpm (or so) though, it seemed to go hard, like it usually does on cold nights. (although tonight was probably colder than most).

I couldn't tell you what sort of carb it has, carbs are one thing that confuse me, they look the same and I've never learnt how to tell them apart. Anyways, ignition is stock, umm, carb is smallish looking, hasn't been rebuilt for a few years, it has 4 into 1 extractors, with a glasspack on a 2, maybe 2-1/2" exhaust. If that really matters. It is loud as buggery though, especially when you get to 6k. Anyways, enough straying from topic, help me out with the sputter pppllllleeeeeeeeeeeeeeeeeease!?

Throttle dependant mostly, but high rpm seems to not be worried by this trouble. Today, not really a cold day, I had the same sort of troubles with the engine cold, not as severe though, and once it was warm, it basically dissapeared totally.

EDIT: I'll give you some background on the car, it's a 74 celica, so it's 30 years old, but not really a collector, so it hasn't been THAT well looked after, just used and maintained. It probably could do with a carb rebuild, and new filters, and a tune. Heck, it COULD do with an engine rebuild and bodywork and interior and... and...

Ok I think I got it fixed, I decided to actually have a look at it, and my hunch was ignition, so I checked connections and the dis. cap. Sure enough, the lead points were all white oxidised up, so I sanded them, and get better response now at first startup. I can put my foot down further without it choking (free-revving when first started), and while driving, sputtering dissapeared, although it is a warmish day, we'll see when night comes.

Thanks everyone for help.

Okay, another update for those interested. Cleaning the points didn't really do crap. Helped a little, but not really. I was still thinking it was ignition related though, and something was telling me 'too advanced'. The indication may have been the backfires I got on severe pedal (Note pedal not petal. Flowers have petals.) to the metal applications. Luckily I have a groovy distributor with a little clicking twist knob with ADV and RET and two arrows. I clicked it two in the retard direction. Much more power down low, better response and the sputtering all but gone.

EDIT: I'm still not sure how I came to the ignition conclusions, but it seems to have worked. Also, I don't know why it started doing this all of a sudden, I haven't touched the advance for months. I did however get 2/3 of a tank of fuel the day before I noticed the sputtering however, but if anything that would have caused pinging if anything if it was bad right?

Okay third update. Retarding the timing helped a little, but as the first fix, didn't really work after the first try.

I tested the car out last night, and found that it sputters at about 3/4 throttle, but once I floor it, that last 1/8 or so of travel opens the secondary, and the sputtering disappears. - Guessing now blocked primary main jet.

So I did more research and I worked out that yes, it probably is the jets in the carb being blocked. I was worried about tackling a carb, they're one of the complex things I hate. Fuel injection, sure I can handle that, but carbs.... *shudder*.

UNTIL NOW (Insert Dun duh duh DAHHH! music)

I looked at the thing and worked out it is a 32 / 36 DGV Weber carb, and found an exploded view PDF and a parts list to go with it. I worked out the jets must be inside it, and was worried about fubaring the gasket, because I didn't know where I'd be getting weber gaskets from if I did. Anyways, the float bowl had some tiny crud in it, too small to block the jets, as I found looked clear. I cleaned the bowl, and blew the jets out, I took out the power valve and blew that out too, although it appeared to have a ball valve inside it, so I probably didn't do much. So I chucked it back together, had a look at the fuel filter, it looked pretty clean, apart from being on the wrong way. (arrow pointing to tank, but it's been that way for a couple of years, so I doubt that caused anything)

I expected it not to start at all after I put it back together, stuff usually doesn't work when I mess with it lol, but it started in about the same amount of time that it usually takes. Throttle response was a bit better. Whether that it because the motor was in the sun for a while or not is another thing, but I guess I'll find that out. No fuel leaks anywhere.

So I took it for a test drive. Even better torque down low, and the first time I went to 3/4 throttle, a little sputtering, which bummed me a little, but I kept going. Every 3/4 application after that seemed like gold. Very smooth transition from 0 to 3/4 to the secondary opening. Prior to this, when secondary opened, it was like hitting the nitrous button. (I don't have nitrous btw )

We'll see how the second test drive goes. Hopefully it doesn't return to sputtering form like the previous fixes did.

I still have a little hesitation from idle, which I've learned is a lean idle circuit, so I might richen it up, but that's not related.

So I might have fixed it, and I'm not (too) afraid of carbs any more.