I recently bought back a bike I had a couple years ago so I'm familiar with it but have only gotten it to start (and stay running for maybe 5-10 min) a handful of times in the past week. It has 4 carbs which makes the bike so sensitive & I can't seem to get my head around what might be wrong. It always sounds like it's just about to start but just doesn't. Every now & then it fires right up & sounds great. (maybe a little popping at one time & had some grey smoke on the left bank another time) When it gets past the starting stage & actually responds to the throttle it sounds great. I can throttle it all the way out with no problems but it doesnt last long & as soon as I try to warm it up for a few minutes (to adjust the mixture screws & possibly sync them by ear) the revs start dropping & I add throttle only to hear it slowly die down & cough out. It's driving me crazy, people come asking me to try it just to see if it's one of those times they might actually get to hear it start instead of cranking over & sounding so close it kills you to know it's ALMOST there.
So far I bought a new battery & keep it hooked to a battery charger so I know the voltage is good. Bought new plugs & checked all for spark (although the wires could use changing) Pulled the carbs & cleaned everything, adjusted float lvls to just under the rim of the float bowls. Replaced clamps & checked all the boots. I've tried my mixture screws at everything from 1-3.5 turns out & Idle/Sync screws 1-3 turns out. I have to have them close because when it runs its runs well & doesn't smell too rich or bottom out.
Flushed tank, replaced gas & added a touch of HEET in case of moisture. The petcock is direct feed (no vacuum required) The Outer 2 carbs' vacuums are plugged while the Middle 2 carbs' vacuums are T'd together & ran to the intake. The vacuum on these cars always gave me trouble & still doesn't quite make sense how they are designed to work. Some cap them all off or leave one to open petcock but mine doesn't require the feed. I might try removing the middle vacuum lines & capping those off too as I'm running out of ideas.
Any help, tips, suggestions would be greatly appreciated!!
Thanks for your time,
Curt - (firstname.lastname@example.org)