Dont really know at all what may be the problem.Just dont like to see all
these engine problems go unresponded to, on a weekend even.Try checking the
hose that goes to the auxillery air valve.Dont know if a 91 has this
valve.It would be on the right side of the engine near the throdel(sp),but
below it.Attached to the case , under the intake pipes.May need a
flashlight to see it. Look at go westy online cataloge to see a picture of
what it looks like.It is called auxillery air regulater. Try pinching
various hoses with pliers to see if you get a change from sputtering.Good
luck, Roger Sisler.