I bought a 1986 vn750 last year. Marbled, degoated, debaffled, Iridium spark plugs, 30,000 miles. Compression test excellent. The front cylinder has always idled lower than the rear, about 300 rpm difference. It sort of gargles at idle on the front cylinder. About two months ago I fired it up and the rear cylinder would not idle but now the front cylinder idled perfect. Pulled the carbs and cleaned and found rear cylinder idle jet clogged. After reinstalling, the rear cylinder idled fine but the front cylinder went back to low exhaust pressure compared to rear at idle and about 300-400 rpms lower on front cylinder. I am down to the conclusion that my carbs are out of sync? The bike runs perfect but just has the idle issue. Also, it is set at 900 rpms at idle. If I raise the idle to 1200 rpms the front cylinder seem to come to life more but you can tell that is is still lagging behind the rear cylinder by (Guessing) about 300-400 rpms. Will to much vacuum cause this? Its the only thing left that I can figure.....carb sync.