The Howell system doesn't know anything about ignition, other than a tach signal to indicate that it is cranking. The injectors won't fire if there isn't a tach signal. The thing involving grounding A-B is to set the base idle, not related to timing.
Assuming you have a base idle of around 750, just set timing with a light and with the vacuum advance disconnected and the hose capped off. Idle isn't critical here, but you don't want it so high that the mechanical advance might pull in.
I've run my timing at various points over time. Never made any big difference to performance. Howell specifices 8° BTDC ± 2° and it is on the emissions sticker. That might be important if you are in CA and need a smog test. I've run between 8 and 12 and like I said never saw much difference, and that was with the original distributor (nuttered) as well as with the GM HEI that I have now. I've settled on 10° which gets me past the smog test okay.
My vacuum runs 18 - 20 in/hg with a well sealed intake manifold.
Having said all that, based on my experience, I don't think timing will end up being your issue, but of course you do need to check it. Check your vacuum level on port 'A' which is the front facing throttle body port. I'm suspicious of your vacuum. The intake manifold can be tricky to get well sealed. There is also a difficult to seal point under the throttle body around a bolt through the base adapter. You would have to pull the TBI to check it. Supposed to have a mound of RTV which is easy to screw up and hard to find if you do.
Lastly, since I've been dealing with this myself lately, I would check fuel pressure and volume.
Assuming you have a base idle of around 750, just set timing with a light and with the vacuum advance disconnected and the hose capped off. Idle isn't critical here, but you don't want it so high that the mechanical advance might pull in.
I've run my timing at various points over time. Never made any big difference to performance. Howell specifices 8° BTDC ± 2° and it is on the emissions sticker. That might be important if you are in CA and need a smog test. I've run between 8 and 12 and like I said never saw much difference, and that was with the original distributor (nuttered) as well as with the GM HEI that I have now. I've settled on 10° which gets me past the smog test okay.
My vacuum runs 18 - 20 in/hg with a well sealed intake manifold.
Having said all that, based on my experience, I don't think timing will end up being your issue, but of course you do need to check it. Check your vacuum level on port 'A' which is the front facing throttle body port. I'm suspicious of your vacuum. The intake manifold can be tricky to get well sealed. There is also a difficult to seal point under the throttle body around a bolt through the base adapter. You would have to pull the TBI to check it. Supposed to have a mound of RTV which is easy to screw up and hard to find if you do.
Lastly, since I've been dealing with this myself lately, I would check fuel pressure and volume.
