HIGHLIGHTS FROM THIS LAST WEEK

Re-jetting was quite an experience! Easier than I thought, but with a few unexpected challenges. My bike is a 2004 Midnight Star with the following configuration: No AIS, Baron's B.A. Kit & Twisted Curves Exhaust. Here's a few things I picked up along the way:

1. Manuals. The instructions that come with the Baron's Big Air Kit are good, but do not go into detail about removing/installing the carb from the engine; nor do they provide any assistance in balancing the four systems on the carb. So in addiation to their instructions you should have: RS Maintenance and/or Clymer Manual for installation/removal. And for tuning the Mikuni 40mm Tuning Manual was helpful, with the Tech Articles here on the clinic providing essential hints to round out my mini-education.


2. Theory. Make sure you understand the theory of modern carburation. The PMS is primarily responsible for mixture control from 0/0 to 1/4 throttle, and is part of the slow circuit, which also includes the pilot and pilot air jet. The other three systems are part of the main circuit (1/16 to 4/4 throttle). There is a difference between the needle jet (1/16 to 1/4 throttle) and the jet needle (1/4 to 3/4 throttle). The main jet could be removed entirely up to about 3/4 throttle. And yet, all four systems are contributing fuel at all times and a change to one system will affect the other three.


3. Tools Required. I am starting from scratch and with each job I have done on my bike I have been adding tools. Sockets: 10mm shallow and deepwell (for carb heater), Wrenches: 10mm (fuel tank), 3mm & 5mm Allen or Hex Drive, Pliers: ViceGrips Needle Nose and Diagonal Cut, Screwdrivers: Phillips P2 and P3 (air-filter bracket) & a regular flat-blade and 3/16" or 1/8" tip short flatblade (PMS).


4. Adjustments. You should be familiar with the following methods for enriching and leaning the mixture. With the carb right-side up, the PMS screw gets richer when you turn it CounterClockWise (OUT) and gets leaner when you turn it CW (IN). When you move the clip on the needle you will enrichen the mixure by moving the clip further from the blunt end. The following picture circulating on the forum is helpful:





5. Tuning. Is not instantenous or guaranteed. Baron's starts you off with a main jet based on your exhaust configuration, the needle clip on groove four or five based on year, and the PMS dialed out 3 1/2 turns. On my 2004 which has the stock 182.5 Main Jet: I ended up with the current configuration: Main- 175, Clip Groove- 5 (Baron's recommended 4), and the PMS- 2 turns out. Based on my WOT Test I suspect that I need a larger main but will live with moving the needle clip to groove five as this allowed me to go from 3 turns out to 2 on the PMS.

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I believe, in the pic, there should be another washer under the plastic one(between it and the pointy end of the needle).

The effect on the pilot system, by moving the clip one notch on the needle is interesting. Although there is an over lap in the fuel circuts, I wouldn't have thought that would make a difference in the PMS adjustment.

Yes. The order is as follows from the tapered end: washer, spacer, clip, washer. The washer in question is optional and I believe richens the setting by its presence.

sswiss wrote:
Yes. The order is as follows from the tapered end: washer, spacer, clip, washer. The washer in question is optional and I believe richens the setting by its presence.


I didn't realize it was optional. It's the stock configuration, and I thought there was a reason for the silver washer under the plastic one. I was pretty sure that Baron said to put them all back on the new needle the way they came off the old. I have noticed, that adding a second washer, is the recommended way to get a half step richer or leaner.

the last washer is needed to keep the steps at a full step. by going to the 5th groove and leaving out the washer you are at step 4.5 on the needle.

All manufacturers have their instruction for jetting on the rich side. It's a liability issue, jet too lean and you can damage the engine, jet too rich, all ya get is lousy gas mileage, fouled plugs and excessive carbon build up.

The effect of the pilot ckt fuel on the main jet circuit is negligible as far as the over lap of circuits. As throttle increases, vacuum decreases and less fuel is drawn thru the pilot ckt. As well as the main jet plays a very small role in cruise mpg. Cruise speed as per Mikuni is 65mph. I tested this by going up in main jet to a 190 when I normally would have a 167.5, but by not getting heavy handed on the throttle, my cruise mpg did not drop anymore than 1 or 2mpg. Theory is theory only in a fully controlled testing, but does not hold 100% true in real life.