I have a 1982 R100RS with 60,000 miles. I purchased it last summer with 59,000 miles in good condition. I recently replaced the original ignition system with a Motorrad Elektrik kit, and replaced the throttle cables as well. In order to bring it back to base tune, I did a valve check while cold (0.006" intake, 0.008" exhaust), and adjusted the timing.
I read Snowbum's guide for syncing carbs as a starting point, then launched into making those adjustments today; using the vacuum gauge method. After taking the bike out for a ride and setting it up in front of fans, I proceeded to first adjust the idle screws, then the mixture screws, then sync the cables at off idle speeds. Somewhere in the process I got myself turned around because I was having a hard time either getting the engine to smooth out, getting the gauges to sync, or getting the RPM's to come back down to idle after a throttle blip to clear things (it would rest at 1500 then drop to 1000 after 5 seconds). To simplify things, I then reset both mixture screws by turning them 2 rotations out (per Snowbum) and starting fresh. However, at this point, idle adjustments would either yield a runaway RPM condition, or the bike would die. So, I started leaning both carbs out 1/4 turn at a time and attempting to get a decent idle each time with idle screw adjustments. However, I couldn't get the feel for it, or get a decent idle that the bike would return to using this technique.
During this time, I noticed the ventilation air flow temp coming off the left jug was noticeably hotter than the right (oriented as sitting on the bike). I got out my infrared thermometer and while running, measured about 340 F on the right jug right where the exhaust pipe exits the head, and 520 F on the left jug. I know exhaust temps are very affected by fuel mixture, but to make sure I wasn't going down a rat's hole, I decided to do a compression check.
It turns out, the left jug (the one at 520 F) showed 105 PSI, while the right jug (at 340 F) showed 85 PSI.
So, the question is, are these numbers low enough, or perhaps different enough that I need to fix this issue BEFORE continuing to sync the carbs, or are those exhaust temp differences I observed due to my poor tuning attempt and I should keep at the sync efforts and let the cylinders and compression numbers alone?