carb sync question

[Nightcorona]

Ok on 84 gl1200 interstate when you turn the carb screw in that is opening up the air and reducing the vacuum correct? I created one of those DYI 4 bottle setup but it failed horribly with coke bottles. They kind of imploded. I then tried Starbucks bottles and the seal wasnt so good but I noticed that the #4 bottle had way more vacuum then rest. Just adjusting them by ear i noticed that you can get the valves to tap or not tap.

 

[dan filipi]

I've never heard of using bottles to sync but opening the throttle plate more would decrease vacuum at the sync port fitting next to the cylinder head. Think of it like putting your hand over a vacuum hose closing it off, a higher vacuum, moving your hand off the end, a lower vacuum.

 

[Denver]

Read up, :read: then bench sync them :yes: before you try to get them running right on the bike. :good:

 

[slabghost]

Nightcorona » Thu Sep 08, 2016 6:51 pm[/url]":3p14sni4]
Ok on 84 gl1200 interstate when you turn the carb screw in that is opening up the air and reducing the vacuum correct? I created one of those DYI 4 bottle setup but it failed horribly with coke bottles. They kind of imploded. I then tried Starbucks bottles and the seal wasnt so good but I noticed that the #4 bottle had way more vacuum then rest. Just adjusting them by ear i noticed that you can get the valves to tap or not tap.

A lot get this mixed up. The carb screw is likely the air fuel mix screw. Which has nothing to do with synchronizing. Carbs are sychronized by adjusting the linkage to each carb throttle. If memory serves carb 3 is non adjustable. The others are adjusted to match that one. As suggested a bench synch will get you in the ball park a reduce frustration in the process. Now to adjust the mix screws. Start with a warmed motor and set the idle at 1000-1100. Adjust the first carb mix screw to achieve the highest rpm you can get. Not just by the tach but listen too. Set the idle back to where you had it and adjust the next carb mix screw again to highest rpm you can get. Do this to all four carbs. Then do it once more to all four because adjusting one affects the others. Once you've adjusted them all twice you should be good.

 

[fivestring]

+1 what Slab said. Synch screws and mixture screws are two completely different animals. Make sure you are turning the screws with the locknut on the linkage when synching. Tiny, tiny adjustments make big differences. Just putting your screwdriver on the screw will alter the vaccum to that carb.

I recently made the same bottle synch tool using Gatorade bottles. I also had the same imploding situation. What I did was use (two) one gallon glass pickle jars. The glass holds up to the vacuum without collapsing. I found you only really need two containers at a time. Synch #1 to #3 (the benchmark), then switch to #2 and #4, then finally adjust #4 to #3.

The bottles with colored water work excellently as a synch tool. With large volumes of water, you have lots of time to make very fine adjustments to get the balance equal. I had previously used another homemade manometer using 4 long pieces tubing and tranny fluid. But this pickle jar setup is far better! I used it to balance my oem carbs but then I did the single carb conversion.

Just make sure your vac lines going into the containers are sealed very well. I had one leaking a wee little bit and it threw everything off. I used hot glue to seal the lines into the metal pickle lids.

 

[zman]

The guys got it right, there is one baseline carb that is non adjustable on the right side, thought it was #1 but maybe wrong and it is #3, find it first and if it needs adjusted up or down on the baseline carb you use the idle screw located below the faux tank where the throttle cables hook up..then adjust the carb along side it to match adjust idle again if necessary
Move over to the left side and do the same adjusting the idle if necessary then thirdly there is an another adjustment to sync the left side bank of carbs to the right, sometimes this left/right adjustment will disturb the original adjustment so it should be checked throughout the whole sync process, as well as keeping the idle down to near idle speeds.