The initial 600 mile service for the Yamaha FJR1300 calls for an EFI (electronic fuel injection) "throttle body synchronization". At every 4,000 mile service after that the idle speed and throttle body syncronization should be checked, and adjusted if necessary.

I do most of the servicing of my bike myself, as I am moderately comfortable with mechanical stuff, and want to be sure it gets done right. I bought the official Yamaha FJR1300 SERVICE MANUAL to guide me. I have now done this procedure multiple times. The work you have to do to prep for this is almost identical to what you have to do to change the spark plugs, so you might want to combine the two service items.

Initially, I borrowed one of the Twin-Max carb sync'ing tools so highly regarded by oil-head BMW owners. Unfortunately, I didn't have much luck with it and had to give up. Some folks favor the Morgan Carbtune II, from the U.K., but I bought the tool that my favorite motorcycle shop uses, namely, a Motion Pro "economy carb tuner, for $35. It worked great!

The Motion-Pro carb tuner looks like this. I hang it on a step ladder which I park close to the handlebar, or use this simple front-end stand. The only tricky part was figuring out where it hooked up, and what to adjust. The shop manual provided the answer.

Oh, by the way, the various brass adapters provided with the Motion-Pro kit aren't needed to do the sync on the FJR1300. The plastic hoses fit directly on the throttle body nozzles.

It described how to raise the front of the gastank, which I'd already done previously when mounting a power outlet. It also specified removing the "T-bar" which I found was an unnecessary step, so I left it attached. I blocked up the front of the tank with a 9" scrap of plywood. This works fine if your tank is fairly full, but if it is quite low (one bar showing) you won't be able to get the engine to run.

Warchild favors using a 10' piece of small-diameter rope to loop under the tank's front bracket and tie to the rear of the bike somewhere (like the luggage rack or the crossbrace under the passenger seat). If you do this, be careful to not raise the tank too much. The two pairs of wires running to the two connectors on the underside of the fuel gauge don't have much extra slack, and it would be easy to break one by raising the tank too far. Of course you could just disconnect them -- but then you'd have to remember to hook them back up when you're done...

Note: Yamaha numbers the cylinders left (#1) to right (#4) from the perspective of sitting on the bike in the riding position. Thus the #4 cylinder is on the end of the engine nearest the cam chain housing.


You have to remove 4 small rubber caps, each with a small wire retaining clip. Be extra careful removing these, as they are very easy to lose. I used a small pair of ignition pliers to do the job. A trick I used the 2nd time I did this was to string a bit of safety wire through the small wire retaining clip as shown in the photo above. I left the wire on until I was all done an put the rubber caps back on.

Note: a number of folks who have done this EFI sync have lost one or more of their little wire retaining clips. Apparently, that doesn't matter much. So if you loose one, don't worry about it. The rubber caps appear to stay in place without them. However, if you lose one of the rubber caps, you must replace it!

There is one cap on the top of each throttle body -- the green arrow in the photo below shows the location of the cap on the #3 throttle body (its barely visible behind the gray plastic electrical connector).

This (above) is the right side of the engine, where the #4 cylinder is (you're supposed to use the #3 cylinder as the baseline). Each of the 4 vacuum lines attach to a small brass nipple (which you can see better in the photo below).

The upper red arrow points to vacuum line #4 from the Motion-Pro tool, the lower red arrow identifies the screwdriver inserted into the #4 cylinder's air screw used to make the adjustment.

The photo above shows the left side of the engine. The arrows show the vacuum line attached to the #1 cylinder's nipple, with the screwdriver in the #1 cylinder's air screw. The vacuum line plugs directly onto the nipple, the Motion-Pro adapters aren't needed.

The way things are laid out, the #1 and #2 air screws point to the left side of the engine, and the #3 and #4 air screws point to the right side, which makes it fairly easy to reach them with a long narrow-bladed screwdriver.

The syncronization itself is almost trivial. First, warm up the engine for a few minutes (I waited until 2 bars showed on the temp guage), then hook up the carb sync'ing tool and check the levels. Mine were out of balance, but not horribly so. I just adjusted the #1, #2 and #4 screws so their levels matched that of the #3 cylinder. That's it!

Yamaha says in their Tech school for Yamaha mechanics that you should not end up with any of the adjustment screws bottomed out. A number of folks have reported they had that problem with the #2 cylinder, trying to match it to the #3 cylinder. Since Yamaha also says that at idle the FJR should pull 25cm of vacuum, you could first adjust the #3 cylinder to 25cm and then continue to adjust 1, 2, and 4.


The left photo above shows how far the throttle bodies were out of sync at the 8,000 mile service. At the 600 mile service they were much further out of sync. The photo on the right above shows how close they were after I was done sync'ing them. BTW -- the Yamaha spec calls for them being within 10mm of one another (the black horizontal lines on the gauge in the above photos are 20mm apart). By that measure, my throttle bodies definitely needed sync'ing...

It probably took me a minute or less to get the throttle bodies sync'd, with about 15 minutes on each end to gather and put away the tools, read the directions, disassemble and reassemble the parts, etc.

Another use for the 9" scrap of plywood is to push the rear edge of the gastank forward so as to get the two retaining bolt holes at the top of the tank near the steering stem to line up properly.

The official directions, per the FJR1300 SERVICE MANUAL

Prior to synchronizing the throttle bodies, the valve clearance and the engine idling speed should be properly adjusted and the ignition timing should be checked. (I checked the idle speed, but assumed the valves and ignition timing were OK)
  1. Stand the motorcycle on a level surface. (I put mine on the centerstand)

  2. Remove the rider's seat, the fuel tank, and the T-bar. (I simply raised the front of the gastank and blocked it up with a 10" piece of 2x4, and left the T-bar in place)

  3. Remove the 4 rubber caps. (I warmed my engine up prior to this step)

  4. Install the carb sync tool. Install an inductive tachometer onto the spark plug lead of cylinder #1. (I relied on the dash-mounted tachometer instead)

  5. Install the fuel tank. (I never removed mine so I skipped this step)

  6. Start the engine and let it warm up for several minutes. (My engine was still properly warm at this point)

  7. Measure engine idling speed (should be 1,100 to 1,000rpm) and adjust if necessary. (Mine was within spec)

  8. Adjust the throttle body synchronization. After adjusting each throttle body, rev the engine 2 or 3 times, each time for less than a second, and check the synchronization again.

  9. Recheck engine idling speed, and adjust if necessary. (Mine was still fine)

  10. Stop the engine and remove the measuring equipment.

  11. Reattach the rubber caps and retaining clips, reattach the gas tank, and resinstall the seat.

The specs say that the vacuum pressure at engine idling speed should be 33.3 kPa (250mm Hg, 9.8" Hg). The Motion-Pro tool is calibrated in cm Hg, but the marks are off by about 1 cm (I used a ruler to verify this). I made sure my #3 cylinder was right at the recommended 250mm Hg. The max. difference in vacuum pressure between two throttle bodies should be 1.33 kPa (10 mm Hg, 0.39" Hg).

Note: Colin Whitmore wrote in: "if you live at high altitude, the correct vacuum pressure number will probably be lower than 250mm Hg. For example, in Denver, Colorado, you should use something like 200 to 205mm Hg. It's probably worth the time to do the pressure conversion for your altitude."

Copyright © 2002-2005, by H. Marc Lewis. All rights reserved.