Installing a Genesis Carburetor

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

Installing the New Intake Manifold

To install the Nemesis, Super-G type intake manifold, first check the fit without any rubber o-rings. Slide the manifold in from the bike's right side, little by little. Wiggle, but do not force. Too much pressure and you could damage the manifold or the heads. They are aluminum, and easily dented, scuffed, and scratched. Be careful of the mating surfaces.

If the manifold won't go in without force, try the following: File, sand, or grind the manifold along the top (upper) edge of the 'ears' of the mounting flanges -- especially for the flange associated with the front head. Every engine spacing is a little different; if filing is needed, take a little off at a time, and trial fit as you go. In any case, be very careful not to take too much off. See photo below.

yamaha road star roadstar, genesis carburetor install nemesis manifold

Important Tip: Be sure to leave a minimum of 1/16" between the manifold's o-ring groove and its upper edge.

Once you have a good fit, coat both manifold o-rings with some silicone grease, and insert them fully into the groves of the manifold. Then smear a thin coat of the silicone grease onto the mounting surfaces of the heads.

Next, carefully slide and wiggle the manifold into position. Be very sure the o-rings stay in position as you line up the manifold bolt-holes with the corresponding holes in the heads. Double check that the o-rings are seated in their grooves by examining around the manifold, and looking down the manifold's throat with a handheld light. If necessary, file a little more from the 'ears' to get the right fit. Take your time, and get this step right; it is crucial.

Then begin installing the four manifold bolts (with washers). Special care must be given that you don't cross thread a bolt. Wiggle and coax the manifold so that you can start each bolt using your fingers. If the fit seems off enough to disallow this, check the o-ring installation more thoroughly. Chances are, at least one o-ring may have jumped its groove, or you may just have to file a bit more off the manifold 'ears'. There are many close fitting surfaces coming together here. Look closely to see what the hang-up is. Don't just assume more grinding/filing will result in a looser fit.

After starting one bolt, go on to the next. Do not tighten any bolt down beyond the first couple of threads before beginning the next bolt. Oh, and feel free to wiggle/rock the manifold a bit to help each bolt get started more easily.

Tip: I like to use a little anti-seize compound on the lower third of the threads for most nuts, bolts, and screws around the engine. This is required for stainless steel fasteners, but I use it for others as well -- anywhere that aluminum, high heat, and steel come together. The anti-seize compound keeps the aluminum from sticking too hard to the steel fastener, preventing galling (thread tearing). It also helps get the first threads meshing more easily -- reducing cross-thread potential.

Once you've got all four mounting bolts started, you can begin tightening them down, but first recheck that the o-rings are properly seated; really look closely. Once you're satisfied with the o-rings, tighten the manifold bolts little by little in a criss-cross pattern. Use 7.2 ft-lbs (86.4 in-lbs) of torque -- snug, but not too tight.

At this point, reinstall the upper motor-mount bracket. Use 35 ft-lbs of torque. In other words, the bolts must be tight, but be careful not to strip or over-tighten.

Fitting the Fuel Hose

yamaha road star roadstar, genesis carburetor install

Next, decide on a path for your fuel hose. Whatever pathway you choose, use the following criteria:

  • Keep the general direction of the hose moving downward as it runs from the tank toward the carb, as much as possible.
  • Make room for a fuel filter somewhere along the line. Tip: I also wrapped a piece of old, rubber inner-tube around the filter, as thermal insulation.

To begin fitting the fuel hose, temporarily mount the fuel tank. Tip: If you'd rather not go to that trouble, just know that the tank's petcock sits 3" directly above the chrome, external oil tube connection on the front cylinder (left side of the bike, of course). Then, to install your fuel line the same way I did mine, do the following:

  • Starting at the tank petcock (or measurement point 3" above the front cylinder's left-side external oil line), guide the hose back, just under the top engine mount, between the cylinders and below the manifold.
  • Select a location for the fuel filter along this path, then mark the hose at that location. Remove the hose and use a hose cutter or sharp knife to squarely cut the hose at the mark-point.

Next, put the measured hose piece onto the upstream end of the filter. Then push the remaining hose piece onto the other end of the filter.

Install and tighten a small hose clamp onto each of the two hose pieces, at the filter. Then slip another clamp onto the tank petcock end of the hose. Tip: Check one more time that the filter is oriented in the right direction.

Now, if your tank is on, install the hose onto the petcock, and tighten the clamp. Then guide the hose and filter between the cylinders, as before. Do not further fit the hose until the carb is installed.

OK, now one more thing before mounting the carb. I'd suggest, as others have also recommended, that you make a simple modification to your new Genesis carb: Replace the tiny, short, stub of a breather-hose for the Pilot-Air vent (see the Parts/Materials Needed section on page 2 of this article for details on this). It sits right below the carb's intake throat (at least on my carb). Since it is so short, and has no filter associated with it, I feel that it may be prone to two issues:

  • Since the end of the hose points directly into the oncoming wind, when the bike is under way, it may make the pilot mixture difficult to tune. The faster the bike goes, the more air is ramed into the vent, and the leaner the mixture becomes. Although the effect may be small, the fix is simple, and at these prices, I wanted to get it right, and then forget about it.
  • It might intake dust and dirt.

The solution, for me, was to replace the original tube with a much longer one, up and over the carb's intake throat, and down the 'down-wind' side of the carb. This way, I feel that air can be asperated as needed (without any ram effect), and there is significant protection from inhaling debris. See photo below:

yamaha road star roadstar, genesis carburetor install pilot air

 
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