1980 sg carb inquiry for #2 mixture setting

[vedgar]

This is the first time the carbs have been apart. Factory setting for 1, 3 and 4
mixture screws were 3/4 turns out. This puts the needle just protruding from the carb body about 1/32 of an inch. Carb #2 setting was 2 1/2 turns out and the tip of the needle not protruding from the carb body. I assume the setting for #2 has something to do with the fact that #2 supplies vacuum supply to the vacuum advance and requires a different setting ? Hmmm. I am reasonabley sure the carbs have never been tampered with as the plugs for the screws were intact. Reasons for disassembly was thorough cleaning after years of sitting idle. Another post mentioned the same concern for #2 idle mixture screw, but no reason was given for it being a different setting than the other 3 carbs. Well , what is the reason and what should an initial setting be for pre-synch. Appreciate any help and thanks in advance from Vance.

Vance
P.S. I have exhausted the internet for answers

[jetmechmarty]

I think I used two or two and a half turns when I put my carbs together. That was for all four. That and a good bench sync and I was good to go. I could have left it like that and been happy with it.

After the bike was up and running, I used the carb sync tool to dial in the mixture, then synced up the carbs.

[DGXSER]

I have to admit I have never opened a set that was still at factory settings, so I have no idea if your discovery of 2 being so different is consistent or not.

Very similar to Marty, I start at about 2 turns from lightly seated for all four mix screws. I also use the bread tie bench synch process. Never had a set not fire off well from there. Easy to fine tune and perform a running synch from those settings.

[mack]

Plugs

what does the #2 plug look like in comparison to the other 3?

[vedgar]

don't know yet

Bike has original tires and 2200 miles. Original Owner mothballed it many years ago. I replaced a bent intake valve and am in the process of cleaning the carbs. I had it running and synched the carbs, but low end performance had me rethink ( do the damned thing again) with new pilot jets. I have owned a 79 special for about ten years and only rebuilt the carbs once. It runs great.
Vance

[mack]

Tuning

Mine sat for 18 years so I'm familiar with your concerns.
When you replaced the valve did you take the time to clean up the seats? Did you replace the valve guide seals?
At this point I wouldn't be too concerned with factory settings on your carbs. Start with 3 turns on your idle scres. Get them together and properly sync'd to your motor and run it for a few hundred miles with new (properly gapped) plugs.
After five hundred miles or so, pull the plugs and read them. They will be the best indicator of how each cylinder needs to be adjusted (idle mixture).
Resync everytime you adjust the mixture screws. Adjust the idle back to 1100 rpm and ride some more then repeat until you get it fully dialed in.
May take some time until you get it right but hell, it's winter time up here. A crappy ride is still better than no ride.

[mack]

Tire

Forgot to mention, change all the fluids and check the brakes they probably need to be re-done as well and get rid of those tires and put new ones on.

[vedgar]

Great ideas but 6 degrees here this morning

First warm day ,15 degrees and up I will refit the carbs and have another go.
thanks,
Vance

[jjz28]

I, like don, used the breadtie bench synch and 2-1/2 turns out and have rode it like that since. I don't have a synch tool so it has never been synched but it starts and runs really good. I just cant wait to get a proper synch on it and see how much of a difference that makes.

[jetmechmarty]

I, like don, used the breadtie bench synch and 2-1/2 turns out and have rode it like that since. I don't have a synch tool so it has never been synched but it starts and runs really good. I just cant wait to get a proper synch on it and see how much of a difference that makes.

You may get better idle. Don't get too worked up about the sync. A proper bench sync should have it fine. The sync matters most at idle.

[motoman]

I, like don, used the breadtie bench synch and 2-1/2 turns out and have rode it like that since. I don't have a synch tool so it has never been synched but it starts and runs really good. I just cant wait to get a proper synch on it and see how much of a difference that makes.

That setting will get U started on the early carbs. With the later BS34's, which I assume would still be on that 81Special, 3 1/4-3 1/2 out on the mix screws will keep it outa' of the lean-pop scsnario.

[DGXSER]

Here is a thread I posted a couple years back. YMMV.