Im having the same exact problem with mine. I paid close attention and noticed once it backfired and gas shot out of the carburetor gasket. I't probably has a vac leak. I'm taking the carb out again and putting on some gasket spray sealant on the gasket and adding some sealer adhesive on the two tiny plugs that I took off the carb to rebuild it. It might be the problem as well. Mine ran fine just like yours for the first could of minutes then it did the same. Message me if you figured it out, hopefully we can help each other out. I bought an shop manual that is coming in the mail to work on the brakes.
Good luck, keep me posted. My email address is tony.anaya@sbcglobal.net
Thanks
