Rough Starting

[Argeo]

The car is a 77 Carrera 3.0. I recently took the motor out and put back in. I actually did it twice because of a stupid first time error, but anyways. The first time I put the motor back in, the engine ran great. I had just done the valves while the motor was out. Well, I turned the motor off and parked for a day. Then when I tried to start it, it decided it wouldn't. Well I got it to start twice but it was so loud I turned off immediatley. Come to find out the pop off valve that installed during the winter had popped out causing an air leak. I then reinstalled. Well, now when I start the car, it is backfiring out of the muffler alot which I assume means it is running rich. But if it is running rich, shouldn't the rpm's bounce when you let off the gas. If I rev it up to 3,500 and let off, the rpms fall back to 1000 with no bouncing RPM's. Now the temperature outside has changed a lot since it ran great to what it did yesterday. Cold to warm. Any suggestions? Could it be that the car sat most of the winter and just needs a bit of driving or is there something else I should check. I don't think there are any leaks. Should I try adjusting the WUR to lean out a bit and if so should I do warm or cold. Or should I try adjusting at the air meter, again warm or cold? I have a feeling the car will run fine once warmed up but just wondering any suggestions or advice. Should I start with cleaning the plugs. Oh, the car ran great last weekend after the whole air valve problem so I do not think anything was hurt by that incident.

Thanks.