Did you pull the plug yet? It could tell a story rich vs lean

Sanddog is correct, you should buy a cheap lawnmower tach to tell you what your RPMs are ..get closer to this being an exact science than a guess

Carb adjustment basics and standards.

A VERY long time ago carb manufacturers realized there needed to be a standard adjustment/setting for the fuel mixture screw so your average mechanic could accurately tune various carburetors without much difficulty. And here it is, regardless if it's on a car, bike, lawnmower, etc..

The starting position is 1.5 turns out from lightly seated (don't crank it down), and then you turn the screw in or out until you achieve your highest/best idle rpm, and then you turn the screw back just far enough to detect the slightest rpm drop. If this setting is below 1 turn out from lightly seated you need a smaller pilot jet, if it's above 2 turns out you need a bigger pilot jet.

From there it's on to the main jet. Start with a medium jet size for the particular carb you're tuning (we'll say a 110 for the stock or clone carb) and see how it runs. If it bogs at WOT but runs better with a little less throttle you're probably too big on the jet size. If it runs better at WOT with half choke or sounds revvy and poppy, or if you notice your exhaust pipe is getting really hot, you need a bigger jet.

Once you think you're close then it's on to WOT "plug chop" runs (hate that terminology). Which involves bringing the bike up to operating temperature, putting a brand new plug in it, and winding out every gear at full throttle and then hitting the kill switch before you let off the gas and let it coast to a stop. If the plug looks white or an ashy gray then you need to go up a size. If the plug looks black and sooty you need to go down a size. What you're looking for is the porcelain around the center electrode to be a brown color and the outer part a dark color.

Now it's on to the needle (needle jet jet needle is the proper term). You would have already set this at the center C-clip/or stock position for the above tuning adjustments. If you feel a slight bog as you're twisting the throttle/coming off idle then you need to raise the needle/lower the C-clip. I personally raise the needle as far as I can go without getting dark smoke and losing acceleration characteristics, you're looking for a smooth transition.

And after all of that... you go back to the A/F mixture screw and fine tune it as previously described, and then do some overall plug readings to be sure all is well. You're bike should start well with minimal choking, not bog slightly at WOT, and shouldn't snap crackle and pop when you let off the throttle. :tup:

If its bogging no matter what main jet you use, it's possible that your float valve needs to be adjusted. If the fuel level in the bowl is too high it will cause the engine to run rich.
Also what altitude are you at?

Super nice info thanks! Exactly what I need to tune my carb.


I came across this info for 2-strokes maybe for the most part it will work for 4-strokes?

The plug is VERY dark right now. @thepostman4, I'm either right at or slightly below sea-level. Would the needle air/fuel screw on the bottom being out of adjustment cause the bogging and smoking I am seeing now? It really is a pain in the ass because I have to take the whole damn carb off the bike to make an adjustment then repeat the whole process...unless I'm missing something.

That's good information for a 2-stroke with an air screw, but doesn't really apply to our 4-strokes with a fuel screw.

Float height is important too. The standard for it is to hold the carb upside down with the bowl off. The top of the float should be horizontal with the float bowl mating surface.

OK, more information. I found a picture of the carb I took the other day and I THINK I got the fuel/air screw back to where it was before but it's still bogging out. In neutral, when I rev it, it starts to crap out between 3,000-4,000 rpm and WILL NOT go above 4,000 rpm. Any ideas what would cause that?

Did you adjust the valves? That would one of the 1st things to do before trying to tune.

Alright guys, I figured out the issue and I feel dumb now! I NEVER use the choke so didn't really know what direction was what. I thought up was off but apparently up is ON. I have had the damn choke on this WHOLE freaking time. Thank you so much to everyone that assisted me and I'm sorry to have wasted your time. At least some other good discussions took place!!! Thanks again guys! This community really is amazing!

I have adjusted the valves a couple of times. Most recently a couple of days ago to 0.003/0.004 on intake and exhaust.

No problem. Just glad we could help out. You're not the first to do that. Lol

trhere is a special tool you can use to adj the screw, I dont have the link but maybe search past threads

:doh: Well atleast my fingers got a good workout.. :lmao:

Nice tool but won't work with his carb. It has the D shaped end on the idle mixture screw.