Yamaha FJR Forum : Yamaha FJR Owners Forums - View Single Post - throttle body sync issues
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post #2 of (permalink) Old 07-15-2020, 03:40 PM
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Join Date: Jan 2013
Location: Millgrove, ON, CA
Posts: 7,287
Bring the bike is older and perhaps higher mileage... vacuum passages and sync screws can get crudded up a bit, so you can remove all the screws, squirt some solvent down those holes and clean up the tips of the screws.... consult the parts diagram, note there is spring, teeny brass washer and a teeny o-ring around the shaft of the screw... you don't want to be going crazy and losing any of those parts, especially the o-ring, otherwise you're ordering a new screw assembly (~$7).

What I normally do is set #3 to at least 3/4 turn out maybe 7/8. Ignore all the vacuum readings too many variables to nail that down, but you should be "close" and that counts in this case, and only #3, again. Ignore what it is, condition of your aged engine, valve clearances, etc. influences it.... Sync all other cylinders to #3, and if you have one totally closed yet not synced, back out #3 a tad more and re-do. If you're out more than one turn, note the spring that holds it is losing tension to hold the screw from turning due to vibration.
Next valve check, you may find larger differences in clearance to #3 and the offender, but that's not absolutely necessarily true either. In any case, if you adjust all clearances to be equal across cylinders, your sync should become a narrower differential between cylinders.... in theory.

The other thing is, it does not matter which one is the reference screw, if another one lets you get all the others in line, then sync to that.
Note all this applies to Gen1/2, not Gen3+.
Injector cleaning may not be necessary but never hurts, not sure it has a very large effect on sync as the intake draw should be similar anyway. Let's say worst case one is clogged, not firing, then that likely does if one cylinder is not working at all, engine not smooth. Rather than trying injector cleaners, send them off to a cleaning service who can test and tell you the flow rates.

Keep yer stick on the ice....
2014 FJR1300A - Root Beer (sold)
2009 CBF1000A - Sienna Red
1999 VFR800Fi - Pearl Shining Yellow
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