Stage III Rejetting and Intake Mod
Stage III Carb Jetting and Intake Mod
  For years I was resistent to doing more then a Stage I rejet of my carbs. However, I recently found that my bike was lacking power on the highway due to all the additions I made on it over the winter. Mainly the extra weight of the hardbags and the fairing and the higher wind resistance of the new 'Bat Wing' fairing. So I deciced to finally try the Stage III jets and see if I could squeeze out a couple more HP's for my long distance riding.

  I do a lot of riding in all sorts of weather, so I didn't want to be restricted by a TAK or a full 'Bean Box' style intake mod, because they are very susceptable to water injestion into the intake system. So instead, I choose a variation of the 'Bean Box' mod which I calculate still more then doubles the volume of air I can intake while keeping some basic rain protection. To go with this, I chose new Main Jets of #124 and #128.


These instructions are based on the assumption that you have already rejetted your carbs once to Stage I and have the kit. If not, then you will need to buy a Stage I jet kit from Dynojet for about $80. That's so you can get the new needles and clips and also get the drill bit necessary to drill the vacuum slides. They don't sell the Stage III kit anymore, so get the Stage I kit and then buy the seperate main jets that you want (they are only $2 each so buy extras or different sizes if you want to experiment).

Materials & Tools Needed
  1. Basic bike tool kit needed for removing the carbs ;
  2. Sharp utility knife for cutting the air snorkel ;
  3. RTV or similar high temp silicone ;
  4. Carb cleaner and/or a very fine nozzle cleaning tool - (piece of wire apx. size 0.015") ;
  5. Hand file or bench grinder ;
  6. Main Jets #124 and #128 (DynoJet sizes - $2 each). If you don't have Stage I jets already in your carbs, then you'll need to buy the Stage I kit as well.

  Step 1 - Preperation: The first thing you will need to do is remove the carburetors. I won't detail the whole procedure here as it's covered in the Valve Adjustment Task on the maintenance pages. But, in short form, you will need to do the following...
  • 1. Turn off the fuel Petcock and remove the gas tank;
  • 2. Remove the air filter housing and airbox;
  • 3. Remove the two fuel lines to the carbs;
  • 4. Remove the two sub air cleaner hoses;
  • 5. Remove the neck covers and then remove the throttle plate and cables;
  • 6. Remove both left-side fin assy's for more access;
  • 7. Unbolt the forward ignition coil and move it out of the way for more access;
  • 8. Loosen the carb to cylinder couplings and remove the carbs out the LEFT side (service manual mistakenly says right side, but they will only come out the left side);
  • 9. Drain the residual fuel from the carbs and place them on a clean work area.

Step 2:  Remove the cover from the base carb (shown).Do yourself a favor and buy a quality philips head screwdriver and be careful with all screws on the carbs. There's a spring under the cover so it will try and pop the cover off as you uncrew it. Place the cover and spring somewhere safe, then remove the needle retainer by using a small screwdriver and pushing down on it and turning it until the lock tab clears. Then remove the retainer with spring and the washer and the needle with e-clip on it.

Step 3:  We're going to move the E-clip to the 3rd groove (counting from the top down). The first 2 grooves will now onterfere with the retainer, so we'll grind the first groove off using a hand file or a die grinder. Only take one full groove off and clean the needle thoroughly afterwards. Now put the eclip on the 3rd groove (remember, you just ground one off so if you count from the bottom now, it's the 4th groove up). Now put the needle in place, then the washer and then put the retainer back on and lock it. Put the diaphragm spring back in... make sure the diaphragm is seated properly and then put the cover back on. Repeat Steps 2 and 3 for the front carb, taking note of the position of the hose clip on the cover.

Step 4:   Now we're going to do the jets. Shown is the float bowl of the base carb. Take that cover off, being careful of the float underneath.

Step 5:   We're going to replace the main jets. They just screw out. Be careful as they are only made of soft brass. Put the #128 main jet in the base carb. The #124 will go in the front carb. (The base or rear carb gets a bigger jet because it runs hotter as it's blocked by the front cyclinder from cooling airflow). Remove the Pilot (or slow) jet as well at this time.

Step 6:   Clean the pilot jet either by soaking it in some carb cleaner or using a cleaning wire. Be very careful of the opening inside as it's critical that it doesn't get deformed. I found that after 6 years, my pilot jet was almost half the normal diameter from a build up inside. Once I ran some 0.015" wire through it a few times, the opening was back to normal.

Put the pilot jet back in, replace the float bowl cover and repeat steps 4-6 again for the other carb, using the #124 jet now and also taking note of another clamp for a hose on the cover.

Step 7:   We're going to open up the stock intake now to balance out the new higher fuel flow main jets. First of all, you need a K&N airfilter (shown) if you don't already have one. I've heard Unifoam ones work good as well. You can NOT use a stock paper air filter as it is too restrictive. Do yourself a favor and buy the K&N. It pays for itself over time because it can be cleaned and re-oiled every season and lasts a lot longer then the paper filters.

Step 8:   Here's what the stock air filter housing looks like from the air filter side.

Step 9:   Here's how it looks from the engine (or back) side of the housing. That square tube running down is the snorkel and the main restriction in the air intake path. It's only about 1-1/2" square. We're going to modify that.

Step 10:   The snorkel assy just pulls right out of the air filter housing. All the mods we'll be doing are on this piece only, so we can go back to stock by just buying a replacement snorkel from Honda (about $15).

Step 11:   I've highlighted the areas that I cut out. The double chamber oblong tube that extended into the filter area was another huge restriction. Also, the original "Bean Box" mod involved taking the snorkel out completely and then cuting the hole in the air filter housing bigger so that it went right to the edge of filter itself (and the filter then had to be screwed into place to hold in position). There's a lot that I never liked about going that far. Mainly that you had almost no protection from injesting rain with that mod and in a heavy rainfall, you could choke out your engine. So I decided to modify the snorkel instead. I took out the square tube and the part inside the filter, which increases the area over 100% and should increase the airflow greatly, but I left the top of the square tube on and the 'flaps', which are there to keep rain from running down from the tank area and into the air filter housing.

Step 12:   This is how the snorkel insert looks after I cut off the pieces I highlighted.

Step 13:   Here's how it looks with the modified snorkel back in place on the air filter housing. I siliconed all the joints with high temp RTV and if you notice, I also went over the joint on the part that goes up to the airbox, as I found the joints loose on it (and a possible source for air leaks).

Conclusions:   I've been very happy with the results. Going from Stage I to Stage III wasn't a huge increase in power, but you do get a very noticable increase, especially in 5th gear. I find that the engine has enough power again to hold me at 120 km/h in heavy winds and when I'm fully loaded. I never realized how much resistance the new fairing cost me, but I feel that I have compensated for it with this mod. Also, cleaning out my pilot jets made the bike idle much more smoothly and I didn't need to get larger pilot jets, as I feared I might have too... it runs great at low speed as well as high speed, and with the idle mixture screws set at 3-1/2 turns each, I get absolutely no popping on decleration.


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