The brief story; I've owned and maintained this bike for about 15 years. The bike has always started and ran reliably with good power but last seasons I have experienced some stalling while coming to a stop and light popping/ coughing while at idle once the bike was warmed up.
I noticed the front cylinder sounds strong out the back and the light popping/coughing was coming from the rear cylinder. I checked the adjustment on both idle needle valves to confirm not to lean and obtained best rpm on both cylinders. I hooked up my old motion pro mercury filled sync gauge and my tach to the rear coil. The rear pressure read much lower than the front at 1200 rpms but more or less even at 4000. I adjusted the "sync" cable (rear cable front carb) and by slacking the cable quite a bit, I could obtain equal vacuum at both cylinders and stop the light popping/coughing but at this sync cable adjustment, could not get the bike to idle even with the idle stop knob fully tightened, the rpms are so low the bike eventually stalls and I see the idle stop screw doesn't even contact the stop.
Other clues to offer; I did a compression test and both cylinders are at 145 psi with decompression engaged. I also confirmed that the throttle grip cable and both carb throttle cables were slack and not interfering while adjusting the sync cable.
If there is anyone out there that has an idea of what the problem might be, your reply would be appreciated.
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