Lifan 420cc stock, jet question

Brian Boyer

Happy New Years Eve everybody.


Hey on my redneck mud motor the useable RPM range including where the engine rpms will be used is very similar to your carts. My question is on my stock Lifan in its current form what is the correct carb jet kit to get? I dont want to burn this motor up running lean~ especially since i'll be knocking on 5,000 rpms from time to time.

Thank you and be safe tonight.

BGW

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jerryggable

My data will not translate very accurately since I have more mods than you and it is in a gokart but I just drilled out my pilot jet and main jet rather than buy new ones - figured if I went too rich then I would buy new jets. I wound up drilling out my pilot jet with #56 drill bit (.046) and my pilot jet with a #75 drill bit. Again, that will be too rich for your engine setup. I would just keep reading the sparkplug and if you decide to drill them out do not go any more than one drill size at the time. I am sure someone else will have better info for you.

slonomo

The jets are pretty small, I don't know if I would attempt to resize with a drill bit. Some guys use a tiny torch cleaner file type tool and just kiss the inside of the jet a bit, then try it out. You can use your ears to hear the difference, or look for black smoke, or use the spark plug method.

Using drill bits is very tough because one size larger drill bit does not translate to one size jet. It's tough to be precise with this unless you have micro drill bits in every tiny small size imaginable. What often happens is you'll increase 2-6 jet sizes per drill bit.

Another way, not always accurate, is to use mm measurements. Example: #75=.75mm and #100=1.0mm and #150=1.5mm The problem with this is it's not this way between manufacturers. Mikuni #'s don't match Keihin #'s, etc.

Micro drill bits mostly come in metric sizes. I was not able to find drill bits that come in .1 mm increments. Usually go .8mm, .9mm, 1.0mm, 1.2mm, 1.5mm, 1.8mm. and 2.0mm. This leaves lots of jet sizes in between the numbers. Go too big, have to throw the jet away.

If you make a call to Vegas Carts, they will be able to set you up with jetting. Although, I would probably buy their performance tunable carb for $26 as a starting point. That way you can tune it, and it will come with one size larger jet already installed.

Brian Boyer

That actually sounds like a hell of a deal~ i may just go this route thanks

slonomo

You got it!

sho305

I bought a $8 drill set off amazon and drilled it out until it was close. Since I was planning on other mods I just wanted to see some color on the plug. The first clone I used a torch tip cleaner to file it out over and over until it was where I wanted it. Since I had no way to know what jet I needed, either you get the adjustable jet (was $30 then) or you hog the jets out for free. Any change in the exhaust or airbox will change your jetting. I went up at least 3 drill or file sizes on both. I think I posted what I ended up at on my build post in here.