Tech Articles


Repository for all long term Technical Articles on the Road Star Clinic. The list is quite long, so we encourage you to use the site search if you know what you are looking for. You can search for individual words (ie:carburetor, tire, etc...) or short terms (searches are full text for each article).

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  • Installing a Genesis Carburetor

    Installing a Genesis Carburetor


    Some Road Star owners love the stock, 40mm Mikuni, CV carburetor. Others favor their aftermarket Mikuni HSR 42mm or 45mm, while still others are sold out to the S&S Super-G, using an aftermarket manifold.

    However, it is hard to argue with the incredible performance of the Genesis Big Air, 48mm carb from P.S.I. It is an enormous improvement, as others have also written. See Appendix-A for more information and my experiences with this amazing carburetor....
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    Last edited by Tykes_Place; 03-03-2018, 05:42 PM.

  • Dialing in your PMS

    Dialing in your PMS

    There are several methods of approaching the process of dialing in the PMS on the stock carb. This article outlines one method that can used, and which is designed to balance out the other circuits in the carb for best driveability.

    The Pilot circuit (which the PMS screw controls) is responsible for primary fuel delivery at idle and throttle positions below about 1/4 turn (see Bulldog's article for more complete explanation).

    All circuits in the stock carb are functional...
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  • The WOT test (Wide Open Throttle)

    The WOT test (Wide Open Throttle)

    This is a living document and will be ammended from time to time, as needed to make corrections, and as appropriate to accomodate new things as we learn them. We are still learning the benefits and potential misreads that can come from this test, but at this point the feedback has been very good, and it has helped to identify lean conditions in many main jets.

    This is a test that is fairly well known in Harley performance circles, and is now being adopted and adapted to the Road Star....
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  • The "At witt's End Backfire Cure"

    The "At witt's End Backfire Cure"

    Reprinted by permission from Mr Tidy's tech tips

    I report this as a last ditch effort for those who may experience extreme situations where their bikes are persistently backfiring through the intake OR exhaust, AND conventional efforts to fix the problem prove fruitless.

    It is not a panacea for problems that might be fixed through normal jetting and adjustments. I do want to stress that this is not the best way to fix MOST backfiring problems. Usually the correct fix is...
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  • Setting up and Adjusting your TPS

    Setting up and Adjusting your TPS

    The TPS adaptor on the carburetor is responsible for reporting the position of your throttle to the ignition (ignitor). The ignition uses this information to adjust the timing curve on the bike to match driving conditions.

    We have seen some broken TPS's that failed to do so, and the bikes they came in on were somewhat sluggish to drive. To assist those who may need to check, adjust, or replace their TPS adaptors we put together this brief paraphrase of the instructions...
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  • Rejet Your Carburetor

    Rejet Your Carburetor

    Reprinted by permission from Mr. Tidy's Tech Tips

    Re-Jet Procedure
    Many thanks to "Thor"

    This is how to change your jet and needle, for an explanation of how your Carburetor works. Stargazer has a great article by the Mucker at his site. The jetting is not terribly complicated if you remember this:

    Do not disconnect the throttle Position sensor from the Carburetor.
    • Remove the nut that holds the choke cable on the left side, and remove the
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  • Principles of Modern Motorcycle Carburetor Function

    Principles of Modern Motorcycle Carburetor Function

    Reprinted by Permission from Mr Tidy's Tech Tips

    Specifically in application to the Yamaha XV1600 Road Star

    Whatever the motorcycle or automobile, most carbs work on the same principles and internal systems to deliver fuel in the proper mixture ratio to the engine. The actual components within the carb(s) that use those principles vary quite a bit, but their ultimate execution remains the same. They can be broken down into separate “circuits”, called that because, like...
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    Last edited by Tykes_Place; 03-03-2018, 06:16 PM.

  • Pilot Jet and PMS explained

    Pilot Jet and PMS explained

    Some of you have recently sent me notes asking for clarification between Bulldog's Jetting Primer and Mucker's Principles of Carburetion, with respect to what sounds like different explanations of how the Pilot circuit works in the Road Star's stock Mikuni carburetor.

    A careful reading, and a little more understanding about the differences between how gasses flow (air) and liquids flow (gasoline) will help to clear this up.

    After a thorough examination of one of my extra...
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  • Mikuni/Dyno Jet Conversion Table

    Mikuni/Dyno Jet Conversion Table

    Reprinted by permission from Mr. Tidy's tech tips
    Mikuni / Dynojet Jets
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  • How To Adjust the Accelerator Pump

    How To Adjust the Accelerator Pump

    Reprinted by permission from Mr Tidy's tech tips

    On the 40mm Mikuni Carburetor

    One of the problems I've had with the Road Star is a coughing or backfiring out the carburetor through the breather. One of the cures is to decrease amount of fuel injected by the accelerator pump when first opening the throttle.

    Look in the lower right-hand portion of the image, this is the area of the accelerator pump.

    Duration adjustm...
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