Installing a Genesis Carburetor

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Written by Randy Fox (randysgym)   
Sunday, 06 September 2009

First, a Comparison

Before diving into the tools and materials needed for this project, let me show what this carburetor looks like, compared to a few others, for the Road Star.

The machined, billet aluminum, powdercoated, Genesis carb body is a thing of beauty. See comparison photos below, showing from left to right: Genesis Series IV 48mm, Mikuni HSR-42mm flat-side, stock Mikuni CV 38mm. Note in the third photo that the stock Road Star carb is a rotating butterfly type air regulator, while the other two are lifting-slide types. Note also that the Genesis has no need for an accelerator pump, and no protrusions within the throat except the computer designed venturi steps. Note especially, the float bowl sizes, and of course the throat opening sizes.

yamaha road star roadstar, genesis carburetor, hsr 42, compare
Left sides: Genesis, Mikuni HSR-42, stock Road Star Mikuni CV

yamaha road star roadstar, genesis carburetor, hsr 42, compare
Right sides: Genesis, Mikuni HSR-42, stock Road Star Mikuni CV

yamaha road star roadstar, genesis carburetor, hsr 42, compare
Back sides: Genesis, Mikuni HSR-42, stock Road Star Mikuni CV

Tools Needed

Small set of hex (allen) wrenches

Small set of metric sockets & wrench, for removing the upper motor mount and fuel pump brackets

3/8" Socket wrench with about a 1-foot extension (or other suitable tool), for securing the Genesis carb to its S&S Super-G type manifold

Screwdriver and/or needle nose pliers, for removing/securing hose clamps

Hose cutter (e.g. utility knife), for cutting fuel line

Phillips ('+') screwdriver, optional, for throttle cable installation

3/32" hex (small allen) wrench, for installing the P.S.I. end-barrel, for the throttle cable -- at the carb end

Wire cutters, to cut off the excess of the inner throttle cable

8mm or 10mm Open-end wrench (depending on the manufacturer of your throttle cable/s, for tightening cable adjuster nuts. Tip: A small adjustable wrench or pliers could be used instead.

File, belt or drum sander, or grinder, for possible fine-fitting the manifold to the engine. Not commonly needed... but just in case

Soldering gun or torch, optional, for sealing cut cable ends from fraying

Anti-Seize compound, optional, for reducing cross-threading potential

Parts/Materials Needed

Genesis, 48mm, Big Air, Series IV carburetor kit. It comes with the carburetor, a manifold o-ring, a barrel end-fitting (for the throttle-cable inner cable) with tiny set-screw, a Road Star specific metering needle (EK 149-126-097C), and fuel nozzle (151.4), as well as general installation and tuning instructions.

Nemesis Super-G intake manifold for the Road Star, available through Nemesis Racing of Australia, distributed in North America by DK Powdercoating (email: powdercoatka@aol.com) in Southwest Missouri, USA. It comes with o-rings for mounting onto the engine. See photo below.

yamaha road star roadstar, genesis carburetor install nemesis manifold

3/8" (or thicker) phenolic or aluminum spacer for the carb-to-manifold connection -- S&S Super-G type. Tip: I used 7/8" (a 3/8" in tandem with a 1/2" phenolic, shown brown in the photo below) from my local Harley dealer. This spaced my breather (air cleaner) out to its original position. Others swear by the 1" aluminum spacer from Vulcan Engineering. Tip: Basically, the longer the spacer, the greater the performance of the carb -- similar to the 'ram' effect of the high-rise manifolds of the 1970s era American muscle cars. Note: The spacer also offers important insulation from the engines's heat.

yamaha road star roadstar, genesis carburetor install

Breather Box (air cleaner). Most any S&S Super-G compatible breather will do just fine. There are many dozens of styles and brands to choose from... Or you can modify your existing breather's backing plate, like I did.

Breather gasket, S&S Super-G compatible, (assuming none is provided with the breather you purchase). Or use a gasket sheet, and cut your own gasket using the template shown later in this article.

Note: The Genesis, Series IV carb comes with a self contained enricher (choke), which some owners, including me, feel is difficult to reach easily. If you want to keep your stock, Mikuni choke cable, you will need the following**:

  • The Mikuni choke adapter kit for the Genesis carb, from P.S.I.
  • Your stock, Mikuni choke cable, choke plunger, and choke spring
  • A lot of time, steady hands, and special tools to modify your plunger and cable

**Important Note: As of the date of this article, several Road Star, Genesis carb owners (including me) could not get the P.S.I. Mikuni choke adapter to operate reliably without modifying the cable (shortening), the spring (shortening), and the plunger, significantly.

Fuel filter, if you will be replacing your current one. Tip: The stock filter is too big to fit well between the cylinders. I ordered one from my auto parts store (O'Rielly’s). Here’s the Part#: Wix, 33027. Note: This filter has 5/16” male ends.

Fuel hose, 24" or more. 5/16” or 3/8” inside diameter. Note: The fuel tank’s stock petcock is 5/16”, but the Genesis’ fuel fitting is 3/8”. I used 5/16”, sprayed the carb’s fitting with dry silicone, and pushed/twisted hard. If you go with 3/8” hose, you will need to be careful to clamp the petcock adequately so that no gas can leak there. The larger diameter will increase pressure into the carb -- a good thing -- but either size seems to work equally well. Available at local auto parts stores. Tip: Be very sure you get hose made specifically for fuel.

Hose clamps (small) – (qty: 4, enough of them to clamp the petcock, the carb, and both ends of the fuel filter). Available at local hardware and auto parts stores.

3/8" x 1.25"L SAE (non-metric), standard thread bolts, (qty: 2), for mounting the carb. Available at local hardware and auto parts stores.

3/8" flat washers with small outside diameter, (qty: 2), for mounting the carb. Available at local hardware and auto parts stores.

S&S throttle cable end adapter. It's the cable casing end-fitting for the carb end. It must have a sharp bend (low profile), 90° angle fitting, otherwise the cable won't likely clear the underside of the fuel-tank. Important Tip: Also, be sure the S&S fitting is the right diameter for the hole in the top of your carb. At first, I got a short, straight (non-bent) fitting from Barnett. It was the right diameter, and fit the hole perfectly. However, I needed the 90° angle fitting because the fuel tank pushed against the cable and strained it, so I got a new fitting from a friend. It turned out to be 0.5mm larger diameter, and wouldn't fit into the hole. I ended up reeming the hole. P.S.I. says that a small number of fitting manufacturers are making S&S type fittings that are slightly over-size. If you reem the hole in carb to fit your fitting, note that there are two rubber o-rings in the hole that must be removed prior to hole reeming. Plus, be sure to reem the o-rings slightly, too. The diameter of the fitting that fit properly for my carb (before I reemed it) was approximately 5.3mm. The elbow fitting from my friend measured 5.8mm -- 0.5mm larger.

New throttle pull cable, optional. If you do replace your throttle cable, just order it with the S&S type end adapter.

Clear, plastic fuel line, optional but recommended. For Pilot-Air vent. See the end of the Fitting the Fuel Hose section following, for details. I got mine from Home Depot. It is normally for gas powered weed wackers, fuel hose. Brand: Arnold, Part#: GL-0232, Type: Fuel Line for most small 2-cycle engines, 3/32" ID (2.4mm), 3/16" OD (4.8mm).



 
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