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Hello everyone, my problem is with carb #4 on my GL 1200 Interstate. This carb will not sync out of the four, and it appears to not show enough vacuum for the sync gage to work, the needle does not move at all. The little tube going out from the carb to the slow air valve appears to be all plugged up. I've tried putting a thin wire into it but it only goes in so far. I've tried carb cleaner and it just spits it back out in my face. I've tried blowing it out with 100psi air pressure, and ziltch, nada, nothing clears it out. The elbow tube appears to be put in by pressure but it will not budge. Any input from savy members will be greatly appreciated.
 

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Not real sure what you mean. Do you suspect the plug is keeping manifold vacuum from getting to the gauge? Sounds like you might have 2 separate issues. The slow air supply is plugged and no manifold vacuum on #4 cylinder??? Please clarify.
 

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Yeah, you have me confused, too.
#4 carb is the one you balance the rest to match.
 

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I think I would check the compression on that cylinder. As for the vacuum port take the intake tube off and look inside the bore of the carb for where that port comes out.
 

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I think I would check the compression on that cylinder. As for the vacuum port take the intake tube off and look inside the bore of the carb for where that port comes out.
I have always thought that the slow speed air works just like the carb air jet solenoid on the GL1500. Of course not electronically controlled.
That is when manifold vacuum is high (like at idle) the vacuum pulls the diaphragm and vale up opening the port so that air from the plenum can get to the emulsion tubes. When manifold vacuum is low like when you are starting or accelerating hard the spring holds the cut off valve shut so there is no air. (no emulsion) That richens the mixture for better starts asn more get up and go.
If I am right the port will come out in the low speed well inside the carb. If you blow air in the hose or port I think you would only blow bubbles in the gas in the fuel bowl. Might feel a little air come out the low speed circuit ports by the throttle plate.
 

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I think I would check the compression on that cylinder. As for the vacuum port take the intake tube off and look inside the bore of the carb for where that port comes out.
Also check the gauge.....
 

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I have always thought that the slow speed air works just like the carb air jet solenoid on the GL1500. Of course not electronically controlled.
That is when manifold vacuum is high (like at idle) the vacuum pulls the diaphragm and vale up opening the port so that air from the plenum can get to the emulsion tubes. When manifold vacuum is low like when you are starting or accelerating hard the spring holds the cut off valve shut so there is no air. (no emulsion) That richens the mixture for better starts asn more get up and go.
If I am right the port will come out in the low speed well inside the carb. If you blow air in the hose or port I think you would only blow bubbles in the gas in the fuel bowl. Might feel a little air come out the low speed circuit ports by the throttle plate.
Not exactly. Normally the air cut off is open letting air into the emulsion tubes but under high vacuum (deceleration) it closes the valve richening the mixture to prevent backfires. The vacuum port is in the carb throat.
 

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Not exactly. Normally the air cut off is open letting air into the emulsion tubes but under high vacuum (deceleration) it closes the valve richening the mixture to prevent backfires. The vacuum port is in the carb throat.
Are you sure you are not thinking of the anti-afterburn (backfire) valve?????? :rolleyes:
 

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my problem is with carb #4 on my GL1200 Interstate. This carb will not sync [B said:
out of the four[/B], and it appears to not show enough vacuum for the sync gage to work, the needle does not move at all.
Yeah, you have me confused, too.
#4 carb is the one you balance the rest to match.
Clarity needed for an old guy: How did the other three get synced if you can't get #4 to draw a vacuum? Or is that not what you meant?
 
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