Installing a Genesis Carburetor

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

Appendix

Appendix-A, Information and Experiences with the Genesis Carb From P.S.I.

My results are typical of this carb installed on Road Stars.

With other carbs, the Road Star power slowly builds as the throttle is twisted, peaks at about 2,400 rpm, and then begins to drop off at higher rpm. Yes, that's a very slow peak speed. That's why some refer to the Roady motor as a "tractor engine." It's also why you may have been left behind the pack, if you've ever tried to shift your bike at too high an rpm, while on a group ride.

However, Genesis carb -- with its computer designed, finned and stepped throat -- pretty much makes that same, max horsepower available over a huge range of rpm. I don’t know of another product that will offer anything close to that increase. In fact, it’s hard for me to imagine pouring the money into a big bore project without including one of these carbs in the budget. Without it, you’re likely cheating yourself out of half of the useable power (and smiles).

The Genesis carb rivals fuel injection efficiency, while offering do-it-yourself tuning simplicity. It is truly a breakthrough in carburetor technology. Too bad carburetors seem to be rapidly disappearing from our mechanical landscape.

Seeing the sure fate of carbureted motorcycles, I bought my Roady, in part, as an effort to own a great bike I could maintain totally myself. Note: Fuel injection makes at-home maintenance and performance upgrades very difficult.

Now, with the Genesis carb, I can keep up with the fuel injected models, without unduly sacrificing gas mileage. Frankly, when you compare the performance and price of fuel injection to the Genesis carb, it doesn't look so pricey anymore.

Appendix-B, Technical Information on Needles and Nozzles

Here's a list of needles made for this carb, as of the publish date of this article. This information is given for completeness only. It is not necessary to involve yourself in this, in most situations:

  • EK 150-127-099C, useful generally for 74-88" engines
  • EK 149-126-097C, useful generally for 95-103" engines
  • EK 149-125-095C, useful generally for 107-117" engines
  • EK 150-125-095C, useful generally for 107-117" engines
  • EK 149-124-093C, useful generally for 121-131" engines
  • EK 149-123-089C, useful generally for 139-155" engines
  • EK 149-122-085C, useful generally for 160+" engines

The numbers represent needle diamters, in thousandths of an inch. So a middle number of 126 would mean that the needle is 0.126" diameter in its central region. The first number is the Pilot (near-idle) region of the needle's (upper) diameter, and the last number is the needle's wide open throttle (lowest) diameter.

To remove the needle, remove the top of the carb (including the slide assembly), disconnect the cable and spring from the slide, Then use an allen (hex) wrench to fully unscrew and remove the needle-height adjuster screw from the slide. Then push the needle up, being careful not to force, scratch, or jam it.

As you continue pushing the needle up, it will be stopped by the adjuster-screw detent ball. At this point you must use some force to push the needle-head past this point. Just be cautious that the rest of the needle is not jamed against another part of the slide, and scratched.

Once the needle is out, the needle-spring and the tiny, plastic spring cup will come out fairly easily. The cup may need a bit of coaxing to get past the adjuster-screw detent ball, however.

Be careful not to loose any parts. They are small. See photo below:

yamaha road star roadstar, genesis carburetor slide

Fuel nozzles, stainless steel cylinders into which the needles slide, are available in sizes between 150.9 and 152.0, in 0.2 increments. The numbers represent thousandths of an inch, so a 151.4 nozzle would be 0.1514" ID. This information is given for completeness only. It is not necessary to involve yourself in this, in most situations.

Should you need to replace a nozzle, you will need to first remove the float bowl. The bowl is held on with just one, large, nut in the center of the bowl's bottom. Remove the Power-Jet fuel hose before unscrewing the bowl's center nut. Then the bowl will drop easily.

As the bowl is removed, the float assembly will usually drop out with the bowl. Be careful. The float assembly is very delicate.

If the float assembly has not dropped out with the bowl, pull down on the white plastic guard to remove the float assembly. See photo below.

yamaha road star roadstar, genesis carburetor float

Next, the main pickup tube must be removed. This tube is the big one in the center of the carb's underside. It is held in place with 3 tiny allen (hex) screws (and thread-loc). The screws use a 3/32" wrench, as I recall.

Remove the tube screws, then wiggle and coax the tube CAREFULLY out of its seat. The nozzle is held in place via an o-ring, at the base of the main tube.

Before reassembly, be sure to carefully clean off all old thread-loc around the tube's seat area, and inspect the o-ring carefully for damage or wear. Replace as needed. See photos below:

yamaha road star roadstar, genesis carburetor nozzle

yamaha road star roadstar, genesis carburetor nozzle

Also, three different slides are available: Mild, Medium, and Agressive. So far, it appears the Road Star works best with the Mild slide, regardless of the bike's modifications -- at least for the Genesis Series IV carb.

If, for some reason, you do need to purchase a different needle, nozzle, or slide, P.S.I. offers a 30 day exchange/return. This means, you could purchase several needles and/or nozzles, for example. Experiment with which combination suits you best, then return the unneeded parts (in like new condition) within 30 days for a full refund. It's a great program, especially since Genesis parts are of the highest quality, and therefore pricey.

Enjoy.



Questions should be asked in our forum (Use discuss link below). The forum is very active and you stand a good chance of getting your questions answered there. If you would like to leave feedback for the author, or have additional information you think will benefit others, please use the comment section at the bottom of this page.

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DISCLAIMER: This information and procedure is provided as a courtesy and is for informational purposes only.  Neither the publishers nor the authors accept any responsibility for the accuracy, applicability, or suitability of this procedure.  You assume all risks associated with the use of this information.  NEITHER THE PUBLISHERs NOR THE AUTHORs SHALL IN ANY EVENT BE LIABLE FOR ANY DIRECT, INDIRECT, PUNITIVE, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, OF ANY NATURE ARISING OUT OF OR IN ANY WAY CONNECTED WITH THE USE OR MISUSE OF THIS INFORMATION OR LACK OF INFORMATION.  Any type of modification or service work on your motorcycle should always be performed by a professional mechanic. If performed incorrectly, this procedure may endanger the safety of you and others on your motorcycle and possibly invalidate your manufacturer’s warranty.


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  Comments (10)
Good info
Written by zip1700, on 06-13-2012 21:12
I appreciate the write up and the fact that you shared your experience and opinions with us. That is what a good forum is all about, no matter how someone may feel about it, at least we now have a look into it from your eyes. Thanks again
Big Air
Written by 01HotRod, on 04-18-2012 20:36
I have been running the Big Air carb on my 01 Roadstar since 2008. My motor is a 110 c.i. Patrick Racing big bore with 10:25 pistons 2mm oversize valve, Dyna ignition, Monster Pro 2 into 1 header, with no stinking baffle. It puts 110inch Harleys on the trailer any day of the week. With stock cams it dyno's at 85hp and 115ft/lb torque. Will bury the stock 120 mph speed-o, I love it.
Written by comara, on 10-25-2011 14:36
excelente articulo,,me gustaria saber mas al respecto pues me gusta la idea para mi moto
Carb
Written by Starkruzen, on 03-29-2011 18:57
Great article, very detailed and outstanding pictures and tips. A first class white paper. For me, this is a huge project and cost prohibited. A cost and benifit analysis would indicate that, for a novice and experienced Roadie this carb is not the way to go. I have the Maxair HSR 42 on my 07 Road* and I can say that Maxair gives you a "plug and Play" system with a TPS. I got 54.7 MPG and I can stomp a fuel injected Roadie and recently a Fat boy. And the total cost which includes mounting your stock TPS, new SS cables and choke cable which is plug and play for $713.
GAINS
Written by 99xv1600, on 02-22-2010 16:38
You spent 1500 on this and you can now keep up with fuel injected models? What is so special about the injection bikes your riding with? I can keep up with them without this!
Written by ironman, on 01-05-2010 16:19
GREAT article, very detailed, & well written. The price knocked me off my chair :cry :cry
Cost
Written by Rayjay, on 01-05-2010 13:58
Just looked at the website for the carb. It goes for around $1100 in black anodized. :cry  
 
Then you have to go for the extras. Total cost would be around $2000 by my estimate. 
 
http://www.psicarbs.com/store/catalog/index.php
carb install
Written by JYD, on 01-05-2010 01:10
Like everyone else,what is the cost of this project?
Written by texasscott1, on 01-04-2010 22:02
Excellent writeup. Might want to correct the beginning though. Road Stars come stock with a 40mm Mikuni. Also the cost would be nice to know.
Project costs?
Written by Rayjay, on 01-04-2010 21:33
It would have been nice to see the cost of this project for each component and the complete package.

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