Effect of l-carnitine for loosing weight?

Not that much. Not the first agent i would choose for weight loss. Other things are more effective.
Improves weight loss. Study done - one group was given 2000 mg of carnitine, and the other a placebo. In the placebo group, the average weight loss after 12 weeks was one pound. In the carnitine group, weight loss averaged 11 pounds. That’s an eleven-fold increase in weight loss, simply by increasing carnitine levels.