What do you gap the spark plug for a 1999 kx 125

as the spark plug gap gets larger with use (called spark errossion) it is not critical usually 0.7mm is fine

I would try 30 . But you can check manual, or web for specific model.
good luck
Jerry

Hi,would start by taking the head off and have a look at the top of the piston, if it hasn't got a hole in it.. good....the bottom of your plug may have broken off, this may have damaged your rings so you'll have no compression. You'll have too strip it down further. When you're sorted check your oil/petrol mix and your air screw setting then check your plug regularly for discolouring or oiling up. Go for it, and be methodical.

Check your fuel filter, sounds like it maybe clogged or needs replaced, can use a generic gas filter to fix or troubleshoot your problem. Rick

hope this information helps these are Denso Plugs
YAMAHA
YZ125
YEAR 2004-1999 ENGINE 125 cc APPLICATION INFORMATION STANDARD STK# 4049 STANDARD PLUG# W27ESR-V IRIDIUM POWER STK# 5317 IRIDIUM POWER PLUG# IW27 IRIDIUM RACING STK# 5714 IRIDIUM RACING PLUG# IW01-27 GAP 0.024

No they will not fit 02 will fit on I have a kx 125 with badboy graphic witch are 02

Spark plug gap refers to the amount of separation between the center electrode of the plug and the bent tang at the bottom of the plug. Too small a gap and you get a weak spark. Too wide a gap and the plug may not fire every time. Most bikes today have CDI (Capacitor Discharge Ignition ). CDI produces a strong spark and works best with a gap of .35 to .45.

The stock plug is highlighted below. Personally, I would get the $6.48 plug. The heat range is the same and you will not be able to tell any difference in performance. The expensive plug will last longer but you can buy four of the cheaper plugs for what you spend on the stock plug. Please rate my answer. Thanks.

try .35

.5 to .6mm
Don't know what it is in inches...