Re: 99 1100 zxi cv carb adjustments
I have been looking into this a lot lately because I have these carbs and I just can't believe that there is no way to make adjustments. The carburetor itself is pretty simple:
-fixed high and low speed jets
-fixed needle valve and seat controlled by a float arm and diaphram
-a needle jet and seat controlled by a diaphram/spring and venturi
In low speed including idle, there is not much to adjust other than the sychronization of the trottle valves and the idle screw which basically just sets the amount of air flow. The low speed jet goes through a bypass and is fixed. There should be a low speed screw adjustment and I have read that there is one hidden that you have to drill out, but I have not tried.
In high speed (WOT) everything is controlled by the balance between the venturi action, the diaphram/spring and the needle valve/seat. The venturi speed is controlled by the trottle valve position and the design of the air cavity which is why people highly recommend you do NOT remove the choke plates when installing primers. This undoubtably disrupts the designed air flow and likely makes the ski run lean. The spring is the key part here. If the spring has a lower spring constant, then it will open more readily with less air and allow more fuel (richer condition). The opposite is true for a spring with a higher spring constant. In my opinion the carbureator should have been designed with a thumb screw in the back of the case holding the spring in place to adjust its tension.
I believe (just my engineering opinion) what they did in designing the diaphram/spring is leave adjustment for vacuum control. The venturi pulls air out of the back of the diaphram holding the needle valve through 2 small holes near the base of the needle. That creates a vacuum behind the diaphram and pulls the needle backwards releasing fuel from the jet. The vacuum cavity behind the diaphram has a hole/slot through which air can come in to relieve the vacuum. This hole is part of the rubber carbureator stack inside the air box under the flame arrestor. (See attached picture)
So, what I believe you can do is rotate the rubber stack on each carburetor to adjust the amount of air that can enter the vacuum cavity. If for instance you were to rotate them to the mostly closed position, then the vacuum cavity will be mostly sealed off. This means that the venturi will have an easier time creating a vacuum behind the spring and the needle jet will open more easily making the ski run richer.
Seems to me that this is the small adjustment that the designers left in the carburetor.
The air slots are on the right hand side of the picture and the openings can be controlled by rotating the rubber stack.
I have been looking into this a lot lately because I have these carbs and I just can't believe that there is no way to make adjustments. The carburetor itself is pretty simple:
-fixed high and low speed jets
-fixed needle valve and seat controlled by a float arm and diaphram
-a needle jet and seat controlled by a diaphram/spring and venturi
In low speed including idle, there is not much to adjust other than the sychronization of the trottle valves and the idle screw which basically just sets the amount of air flow. The low speed jet goes through a bypass and is fixed. There should be a low speed screw adjustment and I have read that there is one hidden that you have to drill out, but I have not tried.
In high speed (WOT) everything is controlled by the balance between the venturi action, the diaphram/spring and the needle valve/seat. The venturi speed is controlled by the trottle valve position and the design of the air cavity which is why people highly recommend you do NOT remove the choke plates when installing primers. This undoubtably disrupts the designed air flow and likely makes the ski run lean. The spring is the key part here. If the spring has a lower spring constant, then it will open more readily with less air and allow more fuel (richer condition). The opposite is true for a spring with a higher spring constant. In my opinion the carbureator should have been designed with a thumb screw in the back of the case holding the spring in place to adjust its tension.
I believe (just my engineering opinion) what they did in designing the diaphram/spring is leave adjustment for vacuum control. The venturi pulls air out of the back of the diaphram holding the needle valve through 2 small holes near the base of the needle. That creates a vacuum behind the diaphram and pulls the needle backwards releasing fuel from the jet. The vacuum cavity behind the diaphram has a hole/slot through which air can come in to relieve the vacuum. This hole is part of the rubber carbureator stack inside the air box under the flame arrestor. (See attached picture)
So, what I believe you can do is rotate the rubber stack on each carburetor to adjust the amount of air that can enter the vacuum cavity. If for instance you were to rotate them to the mostly closed position, then the vacuum cavity will be mostly sealed off. This means that the venturi will have an easier time creating a vacuum behind the spring and the needle jet will open more easily making the ski run richer.
Seems to me that this is the small adjustment that the designers left in the carburetor.
The air slots are on the right hand side of the picture and the openings can be controlled by rotating the rubber stack.
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