Carb shims for 1200

Posted by Don Seitz, GWRRA #109825 on April 15, 1998 at 13:03:24:

In August 1986, I took delivery of a new 1985 GL1200 Aspencade. As I rode it, I noted the carburetion appeared to be on the "lean" side. It hesitated, especially coming off the line from a stop, and would "flutter" during cruise.

A friend of mine raced motorcycles, so I inquired of him how I could richen the Main Jetting. Here's the situation: Earlier motorcycle carburetor main needle jets allowed the rider to move the Jet Needles up or down via notches in the Needles. I found the GL1200's CV (Constant Velocity) carburetors do not have this feature. There are two methods to enrich the fuel mixture; 1) replace all four Main Jets, or 2) place shims beneath the Jet Needles. My racing friend said "shimming" is a common practice and does not require the removal and disassembly of the carburetors. A cost and labor effective
improvement.

With 19,000 miles logged on the Wing, I made the following modification to enrich the Main Jetting. Since then, I have ridden with this modification and now have 164,000 miles on the clock. Enriching eliminated the "hesitation," and I also discovered several benefits. The engine was "snappier," and I routinely get 45 mpg to the low 50's mpg. Ridden conservatively, the best mileage was 58 miles per gallon, one up. The "worst" I ever had was 38 mpg, and that was really "pushing" it.

At Play Co.'s model department, I purchased a bag of 8 each, "Du-Bro," flat P/N #2109, brass, 3mm thick washers, and inspected all the washers. To remove any burrs, I hand-lapped each washer on Crocus Cloth. The diameter of all the washers were measured with a 0 to 1-inch micrometer to be 0.268", meaning that when seated on the "flat" beneath the Jet Needles and they didn't contact the "cone" inside the Vacuum Piston. This is critical. In addition, I measured the thickness of all the washers. The thickness of the four washers
used were: 0.0233," 0.0226," 0.0235," and 0.02229."

Access in removing the Vacuum Chamber Covers, Diaphragm/Vacuum Pistons, Springs, Jet Needle Holders, and Jet Needles to install the four washers should be performed by the following: On Aspencade and Interstate, remove the fairing lower covers and the inner covers. Remove the top compartment. The removal of the foregoing will provide easy-access to the four screws securing the Vacuum Covers on the four carburetors.

Perform the removal of the Vacuum Covers one at a time. Beneath the Vacuum Cover, the Spring will be located. Take caution so as not to allow the Spring to "fly" out. Push the Jet Needle Holder in and turn it 60 degrees with a screwdriver. Then remove the Jet Needle Holder, Spring (very small, second one) and Jet Needle from the Piston. Slide one of the "Du-Bro" washer over the tip of the Jet Needle. The washer "raises" the Jet Needle, hence "enriching" the Main Jetting mixture. Be careful so the Jet Needle is NOT damaged! Reinstall the carburetors parts in reverse sequence. Inspect the Vacuum Piston for wear, nicks, scratches or other damage. Check the Diaphragm for damage. Make sure the Piston moves up and down freely in the carburetor. CAUTION: Do NOT interchange Vacuum Pistons between carburetors!

Congratulations! Now, move onto the other carburetors, performing the same as described above.

Notes: I replaced the "stock" air filter with a K&N re-usable at 7,000. It has served me very well for the past 164,000 miles, thank you! I highly recommend K&N's air filter.

Posted by Jeff Murdock on April 19, 1998 at 03:07:56:

In Reply to: Re: Re: GL1200 Carburetor Modification posted by Don on April 18, 1998 at 21:17:47:

Picked up my washers at a hobby shop--they should be available at any shop that handles RC aircraft and the like. By the way, Don specified in his post that the washers were brass. I checked with two shops and they both told me that DuBro didn't make the #2109 in brass--only steel--so that's what I used.

If anyone has a problem finding these washers, I picked up an extra package of eight--enough for two mods. E-mail me and I'll send you 4!

Jeff