My shop is in an over-sized two-car garage attached to my home. My work is a calling, in the theological sense of the word. Ethical and moral questions arise every day – they are hard, sharp, unambiguous and unavoidable.

Tuning pilot air screws

Posted: March 13th, 2012 | Author: Administrator | Filed under: Fuel & Air, Motorcycle Repair | No Comments »

NOTE: the following is for twin cyl. engines – and singles too.  Fours will not idle on one cyl. so an external tachometer is needed to fine-tune them.  But, in general, just setting the screws to the spec listed in the service manual will be just fine.

Setting the pilot air screws is fairly simple.  Raise the idle speed sufficiently that it will idle on one cyl. when you pull the plug cap off the other.  Turn the idle speed down as far as you can without the engine dying.  Turn the screw in/out until you have found the spot of highest idle.  As the idle rises, turn the idle adjuster to keep the idle as low as possible.  You can hear changes in idle speed better at the slowest possible idle.  Initially, make the changes a 1/2 turn at a time and pause for ten sec. or more to let the change take effect – there is a lag.  Once you have found the highest idle, repeat but make the changes 1/4 turn.  Repeat with 1/8 turn changes.  When done, make sure the idle is as low as it will go.
Now repeat for the other cyl.
Replace both plug caps and turn the idle down to 1.2k rpm or so.
That’s it.

If you want to go all techie, you can buy an external tachometer with an inductive pickup – but the old guys did it by ear.


Leave a Reply