I could not find an old thread on this modification. I will put up a youtube video of drilling the two jets. Was really easy job, I took my time going back and forth until I got bit through the opening. I just drilled one size bigger than the bits that fit in the opening, Mine does not idle down unless I manually move the vane, I then can get it to burble at idle. The other running issue that I had was a pop every now and then while mowing. That is gone now. Does not smoke anymore than before. When I hit thick grass just seems to hit the power band, probably not much different than before. I think the engine will run cooler and that is going to help the longevity, the duraforce has new short block that was installed 2 seasons ago.
This is just two-bits from my ancient memory of jetting changes...A jump to "next" drill size may be risky. Jet size changes from a factory (like Weber) are very small, but have big impacts. So steps in drill size may result in over rich changes. I would read your plugs after a few hours. With carburetted systems it is possible to have raw gas wash the cylinder of lubricating oil and accelerate bore and ring wear. This is normally associated with chokes that are left open. :2cents:
I have been around a 2-stroke with the wrong jets(running snowmobile at 7000 ft jetted for 1200ft) lots of smoke and no power. I have a spare main and idle jet if I want to go back to stock. I am pretty sure the ping I would hear from time to time was from a lean condition. You are right plug color will tell or help tell the story.
I hope your talking Number Drill sizes and not Fraction Drills..
Number drills increase in a piece of hair (.003") in the jet size ranges.. Drill Size Chart (Inch)
I think when engineers are designing lawn mower engines they are not thinking of gas mileage like in a passenger car, their thinking of cutting power..
Put video together as I could not find one, All I can say is that there is no adverse effects from mod. The engine is more responsive as before mod when I would throttle down and back to full throttle I had to go into full choke before the R's would reach operating rpm. Once at operating rpm the engine would stay there, now after the mod it hits operating rpm as soon as I place lever at full.
