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Discussion Starter · #1 ·
what should the pressure of each side measure, not the differential pressure, but the gauge vaccuum pressure. Clymer's indicates 40mmHG or less to be in sync...but I want to know how much vaccuum I could expect if I just measured one side alone.
 

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Unless you have a Turbo, there is no pressure at the 5mm ports, it's vacuum.



Not sure what you are looking for, other than a specification. Perhaps you can elaborate on what you are trying to do.



If you are trying to tune or balance your carbs, the measurement is not important; what is important is that the two sides are equal. There are several threads in this forum on how to build a cheap device which is used to balance the two sides.



If there is a measurement, it would have to be expressed at a certain RPM, since the intake vacuum varies with the throttle opening. The more open the throttle plates, the less vacuum at the intake.



Growing up, I got to see this in person, as my mother had a car with vacuum operated windshield wipers. As she accelerated, the wiper motors slowed down. Accelerating up a hill, they would almost come to a stop. At idle, they ran fastest.
 

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what should the pressure of each side measure, not the differential pressure, but the gauge vaccuum pressure. Clymer's indicates 40mmHG or less to be in sync...but I want to know how much vaccuum I could expect if I just measured one side alone.


Sort of off the wall, but how many forum members remember vacuum windshield wipers??

That tells a lot about our ages. I drove several cars with vacuum wipers. I am also an old

***t.
 

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I remember them as a wisp of a youngster, because our rear engined school bus in grade school had them. This would have been around 1963. I recall that because the bus driver would turn a knob for each wiper, and could adjust them from slow to fast.



Back on topic...what was the original question? Can you provide more from Clymer? A lot of us have the Honda specific service manual, so if you have that and can reference the chapter & page, we can all look together.
 

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Discussion Starter · #5 ·
Back on topic...what was the original question? Can you provide more from Clymer? A lot of us have the Honda specific service manual, so if you have that and can reference the chapter & page, we can all look together.


I just wanted to find out what Vaccuum pressure I could expect to find if I were to measure one side alone. I understand that sync'ing the carbs is independent of the magnitude at each port but a measure or comparison of the differential pressure between the two cylinders.



Clymer's pg41 step 9. indicates that "If the difference in gauge readings is 40mmHG or less between the 2 cylinders, the carburetors are considered synchronized." That delta seems high, and just wondered what the Pressure range was and what the decay was as the intakes were opened.



I wondered if there was a base line vaccuum pressure that I can confirm I am starting with on each side, or if there was a factory value maybe? I have access to some really nice hand-held digital manometers with damping features and the like and want to have the instrumentation spanned correctly for DP and would also like to check the vacuum for each side.
 

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Absolute vacuum readings vary as to the ambient air pressure, the camshaft specs, and the general condition of the engine. There can never be a "baseline" number. In the old days where carbs had adjustable idle screws, it was possible to maximize the vacuum numbers by going back and forth between the idle mixture and the throttle stop. Once you got the highest idle vacuum reading, it was good.
 

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When I sync my bike the reading on the vac gauge was around 8 inchs of vac on each cyl @ idle .I get both cyls pretty much exactly the same when syncing & no more than .5 inchs difference.As mentioned prev altitude & temp will vary readings but thats the numbers I get.I think this is what you are asking.
 

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For easier and quicker comparison of either side and you only have one measuring device, I suggest you make up a T.



Piece of hose to each port joined by a T in the middle going to the gauge.



Use a vice grip or some other means to alternately pinch each hose leading to the ports.



Disconnecting and reconnecting will most certainly affect the engine speed and therefore your readings. The mere act of measuring something impacts what you are measuring; you want to minimize this as much as possible (Heisenberg uncertainty principle).



Greg
 

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As a note on synchronizing, when doing any adjustment to any carb, remember to open and close the throttle after



each adjustment and then read the guage after it settles to idle. This will result in a more accurate reading.
 

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Sort of off the wall, but how many forum members remember vacuum windshield wipers??

That tells a lot about our ages. I drove several cars with vacuum wipers. I am also an old

***t.


Oh yeah. My first car was a bit older than me, a '56 Ford F150 panel wagon.



Cheers!
 
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