runs with choke only

Spraying your carbs with carb cleaner does not constitute cleaning them. There is clean and then there is clean. You must make sure all the small passages are clear and unobtructed.

use compressed air just after you shoot each passage with carb cleaner trust me 90+ lbs of air is your freind when your cleaning carbs

I had the same problem with my bike. When I had taken apart the carbs and looked in the pilot passages, I saw these bluish crystals. I have no idea what they were, so I tried cleaning them out with little success. Winter rolled around, and I have gone over the procedure of soaking them with SeaFoam deep creep, then getting my electric steamer and blasting the passages with steam until the whole carb was right hot. I did this about 5 times, and I am waiting on carb rebuild kits ordered online.

You really gotta get those pilots clean!

I can see 2 things here;
The first is that if the bike runs fine with the choke on but won't rev when it's off, it certainly isn't running rich, it's running weak. A classic test when riding is to run with the choke off and gradually pull the choke on, if the peformance improves this shows that the bike is needing more fuel. The poor MPG that you are getting will be purely down to having the choke on constantly.
Clean the spark plugs and get the bike warm and running with the choke off and have a steady run on an open road, then check the plug colour, it should be a nice even brown colour, if it's white it's too weak, at the moment with the choke as it is I'd say they will be black and sooty. You need to check for an air leak at the manifold and at the take off points (if fitted) for the vacuum gauges.
The carbs do need to be clean but the pilot only goes to quarter throttle at which point the main jet starts to take over, if all is standard in the jet dept then this may be the issue, a change of air filter to pod or belmouth etc and a more free flowing exhaust will need an increase in jet size, has that been done?

The second thing is a long shot but...... if the bike has ever been stood / left a while is to check the advance and retard weights behind the ignition plate, I had a 750B and the weights seized up and wouldn't throw out, hence the bike wouldn't rev, but it would run. A spray with lube (WD40) should sort that.

Hope that helps.

it just runs bad at low rpms, and it revs just fine. Thats why I was thinking timeing. its like on cyclinder doesn't want to fire at the right time unles theres more fuel and a higher rpm. I can never keep it running below 1200

hate to beat a dead horse but it still sounds like pilots to me. does your bike have points or electronic.

Difficult to cure without laying hands on it, are you basically saying that it runs fine, revs up but just won't tick over?
If all runs well and it revs up above 1200 rpm then I can't see the timing being out as it just wouldn't rev correctly.
At 1200 rpm you are definately running on the pilot jets but you mention that you have worked the pilot screws and it makes no difference, have you actually layed hands on the idle screw, it's been a few years but if memory serves me right then this is in the middle underneath the carbs on a 750B. Someone will no doubt correct me if i'm wrong.
Do you have a manual? If not buy one.
I would start with the air / pilot screws, turn both of them fully in, not tight though, and then turn each one out 2 full turns, try it then and if it still won't tick over then use the idle screw to raise the revs, it should turn with your thumb and finger. On a bike like that it is not unknown for the idle screw to vibrate loose and lower the tickover. You need to get back to basics first I think, let us know if you succeed.

Yep, sounds like the carbs. Use carb cleaner and compressed air like the above poster says. Also if you messed with the timing, then after you clean carbs really good, go back and verify timing. Put a fresh set of plugs in it also. Good luck.

ok so here is what I've been up to since my last pots. I got a dyna S igniton so my spark is a lot hotter and very consistant, timeing is dead on, and took the carbs completly apart and used carb cleaner as well as about 40 psi of air. they are clean as a wistle and still want to die when i try and close the choke. its a starter plunger type so its not a true choke, but the pilot needle still has no affect either. My carb bodies are stripping out when i put my screws back on the float bowls too so I'm this close to saying screw it and buying all new carbs. There goes about two hundered bucks!

Could it be as simple as he's too lean? he mentioned that he has a K&N and "opened up the exhaust" and everything else (jetting included I presume?) is stock.

I was thinking it might be that too. anyone know what the next size up is on the main jets and pilot jets? I'm pretty sure the main is 125 stock. Would it be a smart idea to just get the next 2 sizes up for both?

So I put the old air filter on and it took a while to warm up but when it did, I could finaly turn the choke all the way off and turning the pilot needle finaly changed the rpms too :woohoo: . Im so stupid lol