Help with puckered seams
 

I am making a log cabin on a Pfaff 4.2 with built in walking foot. Some logs are 1 1/2 and some are 2 1/2. Right at seam line where sewed, they look puckered even after pressed well with magic sizing. Any idea as what I could have done wrong? Just spoils the look of the blocks.

Have you checked the tensions - both the bobbin and upper thread tensions?

They might be too tight?

First thing I would check is both upper and lower tensions, per bearisgray. As Tartan mentioned, stitch length can be an issue.

What brand and type of thread are you using? Polyester thread can cause this problem, especially if you just switched from cotton thread, as polyester thread benefits from a looser tension.

Other possible causes are a bad needle (try a new one), the wrong type of needle, and the wrong size needle for the thread you are using.

Definitely fix the problem before proceeding, as this is not something that will "quilt out" later.

ditto to the above ... and add in the following ...

Are your logs pre-cut for each side?
Was the fabric all pressed well before cutting?
Or are you using lengths of fabric, stitching and cutting them off?

Either ways .... by chance are you stretching your logs as you stitch, and causing the puckers?

Sounds like you need to adjust your tension. I would start with upper tension. Loosen it and try sewing on a scrap.

I have a Pfaff 5.0 with the built in walking foot. I have found that it will either swerve or not want to go over an intersection if I am sewing at too high a speed. Maybe just go a little slower?

Presser foot pressure is a possible cause, even with a built in walking foot.

Does that model have a presser foot pressure adjustment?

The stitch tension may be too tight. I just experienced this with a border of a quilt sewn on my sisters machine. The border was wavy, kind of like lightly ruffled. The border was removed and resewn, and all was well with the quilt.