Re: Synching carbs and ignition on 1972 85 hp V4

[Don]

Good point Frank, I overlooked the fact that the cam does have two lines on it…Only the line/mark towards the top of the cam is used for synchronization…
I am assuming you did not mess with any of the cam linkage adjustments when you had the carbs off, correct? So, I am thinking most of those adjustments are probably "OK"/close enough. Did you loosen the carb roller clamp screw while you had the carbs off? If not, its location is probably "OK/close enough" also.
Check to see that the cam is not touching the roller at dead idle. Next, make sure both carbs are completely closed at dead idle. This is probably done most effectively by looking inside the carburetor throats. The engine will sneeze lean if one/both carbs are cracked open/even slightly at idle. The two carbs must open at the same time (be synchronized together), this is accomplished by adjusting that little clamp that connects the two butterfly rods. This adjustment is a tricky one….In the quest of perfection (both carbs opening at the same time), the linkage rod often gets "preloaded", resulting in one carb hanging open very slightly at dead idle. On the other side of the spectrum is too much slop in the linkage resulting in one carb starting to open before the other, this usually results in rough/rich running at off idle speeds. It is near impossible to obtain the "perfect fadjustment/synchronization", especially on an older engine with worn linkages/throttle shafts. So, it is better to settle for a bit of slop in the linkage, than the lean spit/stalling that is caused by having one/both throttle plates cracked open (even just slightly) at dead idle.
The other thing to check is that the throttle are not "preloaded" at WOT. There is a roll pin in each throttle shaft that is visible. Push the throttle linkage to WOT (perhaps an assistant can hold it there). The roll pins should not be jammed against the boss in the carb body casting. There should be just a bit of clearance between the roll pins and the carb body boss’. Jamming the roll pins against the casting boss’ will wear the throttle shafts and possibly knock your sync adjustments out of whack. On the other hand, if the roll pins don’t come near the carb boss at WOT, this is saying that the carbs are not opening completely at WOT. If this is the case, then I would be worried that someone has messed with the other linkage adjustments. The wide open throttle stop is adjusted by the small little set screw in the block that the bottom of throttle arm butts up against at WOT….
I realize this is frustrating, very tough to communicate/understand using the written word. The process is not difficult, but it is critical to follow the instructions in order, starting at step one. Altering one adjustment, can have an adverse affect on a previous adjustment if the process is done out of order.