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how do you know when carb idle mixture is correct??

  • Thread starter Thread starter newbie851519
  • Start date Start date
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newbie851519

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I'm getting ready to do a carb sync for the first time, following the series on bwringer's site. i don't have that special tool that lets you see in the cylinder (the colourtune). when adjusting the #3 idle screw so that the idle mixture is correct, and when adjusting idle mixture on the other 3 carbs, how do i know when the idle mixture is correct?
Thanks
 
Adjust the idle mixture (within the range of 1-1/2 turn to about 2-1/2 turns out from fully seated) until you get the highest, most stable idle. Some carbs won't seem to effect the idle so just make them consistent with the others and you will be okay.
 
The technique for that is to warm the engine to full operating temperature. Turn on a fan to blow cooling air on the the engine. Do your vacuum sync, leave the tubes connected. Start by turning each screw in until it lightly seats, counting the turns as you go. Record that number, return the screw to where it was. Do the same for each carb. Now start the engine, make sure things are stable and idle is at 1000 rpm. Turn the screw on #1 about 1/8 turn (in either direction) listen for a change in engine speed. If it changes, try another 1/8 turn. Keep this up until you find the highest speed. Adjust the master idle speed back to 1000 if necessary. Repeat this procedure on the other three carbs. Since you already have the sync gauges connected, check the sync again. Just peace of mind to make sure things have not changed in that area, too.


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First, the carbs must be in sync. Once you've gotten them in sync you can adjust idle.

The method I've been using is to start out at about 2 turns out on all carbs. I then get it warmed up and idling around 1200 RPM. I then start with the left-most carb and turn in the screw in 1/4 increments. In between turns I look for the RPM to drop. It's pretty easy to tell when that happens. From that point I turn the screw out 1/2 a turn. I repeat on all the carbs, adjusting the idle speed knob to stay at 1200 RPM. I then take the bike out for a ride and when I get back I do a final adjust of idle to about 1000 RPM.

Using the highest-rpm method is probably more accurate but its is really hard. You need to pick up minute changes in RPM. I find it too difficult on my bikes so I use my method.

On my bikes this gives real good results: rock solid idle, good color on the plugs and good fuel economy.
 
DimitriT said:
On my bikes this gives real good results: rock solid idle, good color on the plugs and good fuel economy.
Click to expand...

Same here. Not saying it (highest idle) isn't the right thing to do, but I've never had much luck with adjusting to highest idle. I've used plug color and throttle response, that's about it.
 
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