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Can i use an air flow meter to sync carbs?

  • Thread starter Thread starter beachbum3478
  • Start date Start date
B

beachbum3478

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i dont have any carb sync tools, but my teacher had an air flow meter he used to use on his old bikes. i figured its better then nothing, but i had to take the airbox off to do it, so i wasent sure if it would give an accurate reading on cv carbs on my 82 gs1100gl. heres what i did

removed airbox
raised idle screw to 1700
checked all carbs airflow, set them to the same readings of 6 on the gauge

it does feel a little smoother but i dont know if i used the right tool and also i realized after i was done that i left the vac line attached to the petcock, if that would mess anything up. lines are long enough to just turn my tank sideways and adjust the carbs. bascially, would a vac type carb sync work better?
 
What type of airflow gauge did you use? Any pics of your setup? On the surface, I'd say your carb synchronization should be as-good or better than typical and a great way to do the job (although probably a bit time consuming due to the removal and, I'm guessing, changing the airflow gauge from carb inlet to carb inlet.

Proof is in the pudding.......Did the carbs appear significantly unbalanced when you started? Were the results satisfactory? Leaving the vacuum line attached to the petcock should be a good thing (or not a problem....you'd need to otherwise have fuel free-flowing in the prime position etc) - were you worried about that vacuum line crossing the inlet to the air gauge maybe?
 
I would think there might be differences of measuring air flow before the carb as opposed to attaching a vacuum line after the carbs. Also, the middle 2 carbs should probably be slightly lower with the stock exhaust and it's crossover pipe between cyl 2 and 3.
Do you have a pic of the setup you used and how it's attached or placed on the carbs?
 
it doesnt really attach to the carbs, you just press it against the mouth of the carb and it has a flat circle rubber face that seals around the carb and it reads how much air is flowing through the gauge inlet hole. dont know who makes it, its pretty old tho. i mean i can see the air flow of each carb in about 10 seconds if i wanted to. since i can just jump to each carb real quick and do a press seal with the gauge. no pics tho, i gave the air flow meter back to my teacher.
 
I remember seeing a referance to one of those in an old British car repair manual. Used to sync multi side draft carbs. I'll bet your spot on.

See ya
Buddy
 
Should be ok, but you can make a functional carb sync tool for <$10 with a trip to the hardware store.
 
lurch12_2000 said:
I would think there might be differences of measuring air flow before the carb as opposed to attaching a vacuum line after the carbs. Also, the middle 2 carbs should probably be slightly lower with the stock exhaust and it's crossover pipe between cyl 2 and 3.
Do you have a pic of the setup you used and how it's attached or placed on the carbs?
Click to expand...
I wonder why you'd think there'd be differences? At any rate, what he's measuring is what the engine requires based on the health of that cylinder and throttle opening so it's great info. That there'd be a difference due to cross scavaging or any other reason might very well be likely.....and this would also appear measuring at the vacuum port on the stub......you'd adjust for that.....and so would you using the airflow meter - once again good info.

Now how convenient it is to do all this, swapping the airflow meter 'n adjusting on say, a 4 cyl engine, is a whole 'nother story ;) I say kudo's to him for thinking outside the box 'n giving 'er a try.
 
I have (2) such tools. They are excellent. Good for automotive side draft carbs, corvairs and the like. The float is directly relational to the air going into the carb. I tried to use one on the GS but had fitment problems. Had good success with the carb bank clamped on a bench, shop vac suppling the air flow and the test gauge on the inlet side reading the air flow for each of the 4 carbs. I would sync them at a lower RPM than 1700. The gauge itself is adjustable to keep the float midway relative to different idle speeds and air flow. So lower the RPM and adjust the gauge.

You need to be careful on some carb bodies, like Brit Bike Amal Monoblocs, the front face of the air inlet has holes that lead to the idle mixture screws, so the gauge can either block those air bleed screws, or mis read air flow between carbs due to different air mixture screws adjustments between multiple carbs.

Oh, unless your petcock is faulty, or the line is leaking, the vacuum line to the fuel valve being connected will have no affect on your adjustment.
 
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