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Discussion Starter · #1 ·
Hey, so i checked both of my spark plugs after idling for 10-15min and found a black, dry carbon residue on both L and R spark plugs. The mixture screws are set to 2 full turns out from a light bottoming out. By turning in the the screws a bit, will that most likely solve the carbon build up issue on the plugs by making the mixture a bit more lean? Also, by running the bike on the road for awhile, could that burn the residue off?
My carb jets are set to #70 and #100 with stock exhaust.
 

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I recommend ...
... buy 3 sets of ngk plugs ... and dont try to read your plugs early in the build.

After timing, valves, etc etc are all dialed in ... put fresh ones on and ride 40 miles.

THEN read the plugs.

It is very normal to foul plugs while setting timing... ket alone when adjusting carbs.

Sent from my SM-G930V using Tapatalk
 

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The idle mixture screws are adjusted with the engine at normal operating temperature. Which jets you have installed has negligible effect on mixture at idle and adjustment of the idle mixture screws has negligible effect on mixture at throttle settings significantly above idle.

With the idle set to the correct speed for your bike adjust one mixture screw to achieve the highest rpm. Re-set the idle speed then adjust the other mixture screw. Repeat.

This assumes the carbs are properly synchronized (balanced).

If you would advise us as to which model bike we're talking about I could move your post to the appropriate section of the forum, but, the procedure applies to all of them.
 

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Most plugs will carbon up if the bike is left to idle for an extended period of time. Usually a good run for 30 mins or more will bring them back to represent how the motor is running in a real world riding setup, depending on it's tune and mechanical condition. I would be looking for a light tan colour as a good sign of overall health, yet the amount of ethanol in your gas in the area you live can also play a part too.
 

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Discussion Starter · #5 ·
Thanks J-T. I was going to get new plugs and go for a long ride and check the plugs condition after to then make adjustments

1971 Honda cb350 twin
 
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