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I'd suggest that anytime that you change the intake/exhaust flow characteristics of a carbureted motor that a thorough jetting assessment be done immediately. It's really a very easy process and once done a time or two, it will take less than an hour to fine tune.
It's also important to realize that jetting should be a bottom up process since circuits interact and are additive in nature. The future benefit of fuel injection, if it is applied to the Rhino, will essentially eliminate this process as the sensors and electronic platform will compensate for changes in intake/exhaust flow. The only problem with this is that some flexibility will be lost.
There are basically 4 fuel circuits that need to be assessed each time a component is added that impacts intake/exhaust flow characteristics. They are the idle circuit, the pilot circuit, the mid range circuit and the main circuit and each should be assessed/adjusted in this same order.
The idle circuit is controlled by the air/fuel mixture screw that lies beneath the front most brass plug on the underside of the carburetor body. In order to access the a/f mixture screw, you will have to take a 3/32 drill bit and gently drill through this plug. You want to go easy as once you drill through the plug, you don't want to push through to far and damage the head of the a/f mixture screw. Once drilled through, take a sheet metal screw and use it to grab the plug to gently work it out. Once removed, your a/f screw will be visible. Turn the screw clockwise gently until seated. You will be able to see the tip of the a/f screw in the mouth of the carburetor slightly protruding immediately in front of the butterfly valve. Turn this screw out 2 full turns from the seated position as a starting point. You will need to fabricate a small, stubby flat blade screwdriver that will allow you to adjust while running as it is a pretty tight fit and kind of awkward to adjust when installed. What you want to do is to turn the a/f screw counterclockwise until you feels your engine blubbering a bit. Once at this point, turn the screw clockwise approximately 1/8 to 1/2 turn and leave it at that point that the engine idles best. What you have just done is to set your idle mixture at nearly the richest setting available. As a rule of thumb, if you are below 2500 then your screw will be out about 2 turns and between 2500 and 5000, you'll be out about 1.5 turns and between 5000 and 10000 feet, you'll be out about 1 turn.
The next circuit to assess is the pilot circuit which essentially controls the transition from the idle circuit to the mid range circuit which is controlled by the jet needle/needle jet combination. If you change the intake/exhaust flow characteristics, chances are good that your existing pilot circuit is moving toward the lean side. Typically, the stock pilot jet will perform adequately but if you have a transitional problem such as hesitation upon acceleration, an increase in the size of the pilot jet may be warranted and may cure the problem. If you experience no problems during this transition, then leave it alone and move forward to the mid range circuit. The pilot circuit always provides fuel so it is additive throughout the operating range of 1/8 to full throttle.
The single most significant restriction on a stock Rhino is the o.e.m. intake snorkel between the air filter canister and the intake scoop. The RAIS Power Tube takes care of this restriction. Alternatively, you could simply remove the cover and run an open an open box or you could remove the o.e.m. snorkel and run '04 style. Regardless of what you decide to do, increasing the air flow through this restriction allows you to 'jet up' the Rhino and realize a significant gain in performance even if all else remains stock. The benefit is most readily recognized on the mid range circuit and main jet circuit through increased acceleration and healthier top end performance.
Adjustments to the mid range circuit, which is essentially between 1/4 and 3/4 throttle and accomplishes the acceleration profile, is done next. The adjustment is accomplished by raising or lowering the jet needle in relation to the slide by using shims or washers. Some jet needles have grooves cut that allow the tuner to raise or lower the jet needle by moving a circlip up or down. The Rhino jet needle has a one position circlip so any adjustment is made by shimming. Regardless of the method, adding shims under the circlip raise the jet needle in relation to the slide resulting in a richer mixture. Removing shims from under the circlip lowers the jet needle in relation to the slide resulting in a leaner condition. Typically, I recommend that a tuner swap the thick and thin shims on the stock Rhino jet needle when installing the RAIS Power Tube. I would also recommend this when changing the exhaust tip. This adjustment richens the mid range circuit about the equivalent of moving the circlip down one groove on jet needles that have groove adjustment capability. You will want to shim your jet needle to the point that your best acceleration profile is recognized. Get 3 or 4 small shim washers and add enough washers under the circlip and plastic bushing to result in an overly rich condition and then remove 1 by 1 until best acceleration is obtained.
The last adjustment will be to your main jet circuit which is from 3/4 to full throttle. What you want to accomplish is to have the largest main jet installed that gives you the best top end and does not result in degraded performance at sustained wide open throttle conditions. Degraded performance is characterised by decent top end performance mixed with intermittant coughing or sputtering at sustained wide open throttle. Once you find this condition, you'll want to drop down 1 main jet size at a time until the condition disappears.
At my elevation, which is about 300 feet above sea level, the Rhino is capable of handling 2 turns out on the a/f screw, thick and thin washers swapped on the jet needle and a 155 mikuni main jet with the RAIS Power Tube as the only modification. The addition of a exhaust tip may not result in the ability of running a 155 mikuni main but it certainly warrants finding out where best top end is achieved. For every 2000 feet change in elevation, I would recommend reducing the size of the main jet by 1 as a starting point. In other words, at 2000 feet I would recommend a 152.5, at 4000 feet, I would recommend a 150 and so on. This is only a starting point and you may need to go up or down from there but in every event, your goal should be to identify an overly rich condition and work it down to best performance.
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Roostin' Rhino RAIS Power Tube
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