well, my experience w/ a 235 is that the popping is cuz yer not using the choke to compensate for the non functioning heat riser, and it backfires thru the carb - give it enuff choke it'll pull away smooth w/o hesitation, less choke as rpm gets up, and no choke when it gets warm
not likely the riser was welded in position by anyone, they just rust to death over time - frequently the flap inside has rotted away and headed out the tail pipe - if ya don't have real cold winters, don't worry about it
Bill
