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Discussion Starter #1
Hi!

Borrowed a carbtune (latest mdell) for two cylinders to my motorcycle.
Connected the instrument but at idle it gave no result at all.
Had to rev up to 4-5000 rpm for the meter to move.
What could be wrong !?
 

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Where did you source the vacuum signal? The reading on the carbtune should be highest at idle when the throttle plates are closed.
 

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Discussion Starter #4
Jimi, thanks for your answer.

What is it that makes them not work in the right position?
Does the engine not create enough vacuum?
And what do you do with the scale, it can not be read up and down !?
 

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Discussion Starter #5
Where did you source the vacuum signal? The reading on the carbtune should be highest at idle when the throttle plates are closed.
Connected them at the intake, screw hole.
At idle, no rash at all. however, when the choke was pulled out, the meters reacted.
According to the manual, the value should be 190-230 mm hg. If it's the value of idle, I'm nowhere near it!
Tested with both hot and cold engine, idle speed 1100-1200 rpm
 

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I had the same issue. They advised me to hang the carbtune upside down and that worked for me.
So if you were to purchase again for CXs and possibly all 80's CV carbs?? would you buy carbtune again or the older style manometer (e.g. motionpro)/dial gauges?
 

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Discussion Starter #7
Looked at Motion Pro, seems to be a much better instrument with the calibration in the beginning.

Fluid seems to work better than rods.
 

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Good questions and considerations. I don't know about the cause of the issue. Some carbtunes show this behaviour with some CX's, I know that. But not on all CX's and not with all carbtunes.
Me personally I focus more on the balance rather than the pressure, making the scaling on the device less important for me.
I am not experienced enough with carbtune to give any advice in buying one or not because I know there are enough people who are satisfied with their carbune on their CX.
 

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Q: where in the manual does it say idle should be 190-230 mm Hg? AFAIK the FSM only specifies difference between carbs?

(background : quarantine pet project is a digital sync meter - cheap of course, using ESP8266 - seems to work . Used to have old style guages that worked fine, sold, have carbtune, works as well and also needed upside down trick sometimes)
 

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Discussion Starter #10
Q: where in the manual does it say idle should be 190-230 mm Hg? AFAIK the FSM only specifies difference between carbs?

(background : quarantine pet project is a digital sync meter - cheap of course, using ESP8266 - seems to work . Used to have old style guages that worked fine, sold, have carbtune, works as well and also needed upside down trick sometimes)
It appears in a user manual translated into Swedish, printed in 1981. However, it is not clear whether the value applies to idle or other rpm.
It also states that the difference can be 40 mm Hg.
Question, Should the difference be 40 mm hg or does it indicate the maximum difference ??
 

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That 40 is max. You should be able to get the difference well below that if the carbs are good. I also ignore the absolute values.
 
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Discussion Starter #12
So getting two equal values is more important than the "right" value of the carburetors?
 

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Good questions and considerations. I don't know about the cause of the issue. Some carbtunes show this behaviour with some CX's, I know that. But not on all CX's and not with all carbtunes.
Me personally I focus more on the balance rather than the pressure, making the scaling on the device less important for me.
I am not experienced enough with carbtune to give any advice in buying one or not because I know there are enough people who are satisfied with their carbune on their CX.
not overly experienced with all options either-the Carbtunes seem to be widely used for twins-was thinking of buying for the CX and the adapter kit for the '4s for the CB.
This tread seems to suggest its viable

cheers
 

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I have said many times that a simple water filled U-tube manometer is a more easily used and friendly device. The simplicity confuses most users because the device is so low tech.

Take a clear piece of vinyl tubing. Connect one end to the LH carb manifold, put some water in the tube (roughly 30 inches, clarify in a moment), connect the other end to the RH carb manifold. Hang tube on a vertical board with the bend at the bottom. This will form 2 vertical legs (U-tube), one on LH carb the other on RH carb. The water level between the 2 legs should be equal or level. Place a ruler, tape measure.....between the legs. The ruler will give you the ability to measure the difference in water level in each leg.

Start the bike. The water levels will shift to indicate the vacuum DIFFERENCE between the LH (master) carb and the RH (slave) carb. The manual says to adjust the balance to be within 40 mmHg. Since the manometer is filled with water, we need to make a unit conversion from mmHg to inches H2O. Most of us don't have a bottle of Hg laying about. The conversion of the 40 mmHg is 21.4 inches H2O. So, play with the adjustments to achieve height difference between the water levels in LH and RH legs to be less than 21 3/8 inches.

Cost is about $5 for the tubing. The worst thing to handle is the pulsations from the cylinders, this can be damped with an aquarium fish tank valve. The pulsations exist regardless of measurement method

Advantages: No bouncing needles, reduced confusion between gauges, accuracy is eliminated, larger more sensitive readings, simple to use, easy to store.

Disadvantages: Water could be ingested at start up. Tubing may melt in contact with hot engine parts (exhaust).

If you have doubts......Youtube has videos.
 

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Discussion Starter #16
Interesting reading, you possibly have no link to anyone who did it?
 

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In case you buy a carbtune, do yourself a favour and buy the 4-cylinder type, not that much more money and saves you a lot of hassle when doing a 3- or 4-cylinder engine. And yes, a DIY water type will work, but Í'm a bit silly when it comes to nice tools so I have a Carbtune 4-cylinder kit (had some money once when I needed to sync my carbs :cool:)
 
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I have used a single cheapo ebay vacuum gauge. Swopped it from side to side and adjusted the balance adjustment screw on the bike until the gauge gave the same reading for both sides. Necessary to put some sort of clamp on the tubing to get a steady reading rather than have the needle bouncing about, but otherwise no problems.
 

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Well...that is an execution.

Although, there are several issues which need correcting before a reasonable measurement can be taken.

1. It needs to be vertical. Inclined manometers are used for very fine measurement. We don't need resolution in the single decimal digits
2. NO BUBBLES.
3. Red oil is a more sensitive fluid and will require a taller (longer) system.

Generally, the video shows the intention.
 
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