I am working on this 1968 GT1300JR for a friend of mine and am finding many issues. It ran poorly when I brought it home last fall and spent the winter resolving everything else (wiring, interior, steering, etc). Now that it's nice weather again and most of the rest is done, I'm sorting the driveability. First thing I noticed, when checking the timing, the distributor had not been clamped down. There are lots of little issues like this that have frustrated me throughout. Many various people have been involved in this job over a few years... Now, on to the carbs.
I have read most of the posts on synchronizing DCOEs I could search on these forums (fora) and thought I'd use these instructions as a starting point;
From the Alfa Engine manual. It is the method that I use and I have never needed air flow meters, manometers, etc.
disconnect the linkage that connects the carbs to the gas pedal.
back out the idle speed screw.
back out the synchronization screw.
push up the synchronization arm that contacts the synch screw so that both carbs are fully closed.
Maintain the push on the arm and adjust the synch screw until it just touches the synch arm. I use a .003" feeler gauge.
slowly turn in the four idle mixture screws until they just seat then back them out 1 turn each if you have classic carbs or 4 turns if you have emissions carbs.
turn in the idle speed screw until it just touches the actuating arm, then give it one more turn
Reconnect the linkage and verify that there is some free play in it.
The engine should now start.
Adjust the idle speed screw until you are idling at about 1000 rpm
Turn in each mixture screw 1/4 turn, wait about 20 seconds and see if the revs change. Always adjust them all together as they should all be set the same. You want to find the point of maximum idle speed by turning them all in and out together. When you have it, adjust the idle speed screw for about 800 rpm.
DO NOT adjust the synch screw once you have set it properly.
I followed the sequence posted by alfaparticle
and things would not behave as expected. Tried it again, same issue. Then again without satisfaction.
I ended up making an adapter for an old carb synchronizer I had for various twin carb Minis and an MGB I used to own. The sync showed that the front was not pulling as much air as the rear. A simple twist of the screw brought these into line. I also noticed the first/front barrel mixture screw does not have as pronounced affect as the other three.
It still has a huge bog or misfire between 2000 and 3500 rpm and I can't understand why. It's most noticeable at full throttle but can also be felt when slowly applying power.
Timing is correct. Advance is correct. Points are gapped. Plugs are new and gapped NGK BP7ES. Linkage is a bit tight - keeping pressure on the throttle (closed) when connected (the link from the bell crank to the carb spindles is fully shortened but is still a 1/4" too long but it will connect with a slight bit of pressure). The carb rubbers seem OK with pressure applied downwards or upwards not affecting the idle.
If anyone has had similar issues and can recommend a direction I should take next I would appreciate this greatly.