Reddit mentions of ALPHA MOTO Universal Motorcycle Vacuum Carburetor Synchronizer Synchronization Balancer Carb Sync Balancing Gauge Compatible With Honda Yamaha Kawasaki Suzuki GS KZ XS CB 550 650 750 850 900 BMW

Wait, cone filters? I wonder if the carbs have been rejetted to factor that in. If those cones are restricting air then that's why you're running rich. If the jets have been upgraded too large of a size then that's another reason. I'd find out what your stock carb's jet sizes are supposed to be, then I'd use an online calculator or ask a website that sells jets what size you should have given the mods you've got. And compare that with what you actually do have. So you're still gunna have to pull your carbs to check your jet values. You might even have a clogged air circuit in your carb bodies so cleaning is still imperative.

You could try making your own sync tool but if you have too strong of a vacuum then whatever liquid you're using will get sucked in. This is expensive, but a 'cry once buy once tool': http://www.amazon.com/Vacuum-Carburetor-Synchronizer-Carb-Gauge/dp/B004MSJ7E6

So is his buddy, I'm not sure if you need this for your carbs, I need it for mine: http://www.amazon.com/Motion-Pro-Carburetor-Adjusting-Tool/dp/B001DDH2ZY/ref=pd_bxgy_263_img_3?ie=UTF8&refRID=00QXJ3CH1BBWNM7K2FPZ

You could sync the side carb bodies with a regular screw driver and wrench, but once you move to the center 2 bodies that becomes almost impossible.

Here is a link to your manual that deals with the carburators: http://www.honda4fun.com/pdf_man_officina/pdf_manuali/CB350-400/CB350-400_04.pdf

I would take pictures and notes while doing this. There's not a huge wealth of information for 1972 CB350F carbs unfortunately.

You should register at this forum. Any questions you have they can help you out with: http://forums.sohc4.net/

I'd also pick up this ultrasonic cleaner from harbor freight: http://www.harborfreight.com/25-liter-ultrasonic-cleaner-95563.html Go to the dollar store, dollar general or whatever the cheap store in your area is called and buy a large bottle of LA Awesome and a gallon of diluted water. Stuff makes the dirtiest carbs come out brand new. Maybe be a total scumbag and return the ultrasonic cleaner for a full refund as soon as you're done with it. Should take a day to clean all the parts once your carbs are completely dismantled. Then spray a light hit of WD40 on the metal and polish it off with a paper towel to prevent corrosion.

This is another cool tool to have: http://cdn1.bikebandit-images.com/blog/images/2015/carb-cleaner-kit.jpg If you have an air compressor use a basket ball filling needle to blow all the passageways clean. Or a can of air. This goes without saying but carb cleaner will eat rubber, brake cleaner is almost as strong but safe for rubber.

Random tidbit here is an awesome trick for polishing the float needle seats on a carburator: https://www.youtube.com/watch?v=zlez_hdoWYk when they're dirty it can cause them to stick.

In closing this is going to be a good amount of work and money (Unless you return everything shamelessly) Rubber consumables on your carbs appear to be float bowl gaskets and a few orings, maybe some rubber fuel lines. Nothing too pricey.

Most 75 and 76 US spec 400Fs (400F0 and 400F1) have the flat handlebars as well. My 75 has them. Didn't think the US spec got the high handlebars and forward pegs till 77 (CB400F2).

I agree the starter switch is likely the cause of the headlight problems. The current for the headlight actually flows over that switch. Here's a link to a relay kit that will fix that.

Also the yahoo CB400f group has a set of pictures that show you how to repair the switch if its salvageable. You can also find NOS switches on ebay if you look hard enough.

Good Luck on sorting out the issues and getting it back on the road. I have a good deal of work to put into mine as well.

Some more useful CB400F links:

Electronic Ignition kit.

Honda Sohc4 forums

Honda Service Manuals and Parts Lists

3000 mile maintenance:

• Clean all carb passages -- Try this for badly gunked up carbs: Yamalube Carb cleaner
  
  May need to rebuild carbs if jets are badly varnished.
  
  
• Change oil & filter
  
• Change air filter
  
• Change spark plugs
  
• Adjust cam chain
  
• Check and adjust valve clearances -- need .002in feeler gauge
  
• Check and adjust points and timing (or replace with electronic ignition)
  
• Vacuum sync carbs --
  Carb sync tool
  
  
  
  11mm master cylinder thread on sohc4.net.
  
  
  
  
  
  

Thanks! The problem is that the float bowl is putting pressure on the screw. I can reach the screw, but can't turn it because the bowl prevents it x_x.

I hooked up my gauge to cylinder 1 and no matter where I have the mixture screw the vacuum stays the same. The only time the vacuum changed slightly was when the bike reached operating temperature. I tried adjusting the screw again after this and it maintained a constant vacuum the entire time. No adjustments changed the vacuum - at least not at a level readable by the gauges. :(

https://www.amazon.com/gp/product/B004MSJ7E6/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

That's the tool I'm using.