Tuning 1/4 to 3/4 popping

Okay so i have a 2006 yz 450. I had some motor work done on it and ever since it has this popping or sputter during part throttle cruising down the road. I was thinking the needle position was way off and i could adjust it to get rid of it. Well i have a wide band oxygen sensor i have installed in the exhaust to read the a/f ratio. At wide open throttle i am right around 13.3 to one and it runs great. However when i am cruising along it was around 13.8-14.0 range and it was sputtering or popping once in a while cruising down the road.

I lowered the needle clip one position to raise the needle and richen it up a bit as i thought maybe it was to lean. I think it got worse and was around the 13.5 a/f range. The thing i don't understand is that i have tuned a lot of motors and at part throttle in the cruising range to be at the 13.5 a/f and they ran great and never popped.

So to all the dyno guys out there, do the yz450 motors like to run lean? I don't really want to change needles (as i can't lower it any more then it was), and 14:1 is already leaner than i setup most of my other bikes. I don't understand why it would pop and miss at that a/f ratio.

Try going the other way if that made it worse.

Sounds like it is running rich and unburned fuel may be Igniting on the hot exhaust.

What does the plug look like when you run it at the RPM where it is popping?

I don't pull the plug. it isn't a very accurate way to tune an engine when i have a wide band to show exact a/f. Its just weird as it acts too rich but is showing around 13.8-14:1. bad thing is i can't lean it out anymore as the needle is all the way down. I will need to get a new needle but i don't know what one to get. are the steps in the FCR needles very drastic?

have u tried running it without thr TPS connected.. smoothed mine out!!!:busted:

I don't pull the plug. it isn't a very accurate way to tune an engine when i have a wide band to show exact a/f. Its just weird as it acts too rich but is showing around 13.8-14:1. bad thing is i can't lean it out anymore as the needle is all the way down. I will need to get a new needle but i don't know what one to get. are the steps in the FCR needles very drastic?

Try dropping the main jet 1 size.

I don't have a cool electronic gizmo to check my bike to see if it is running lean or rich. So basically those numbers you posted mean nothing to me.

I am sure there are people on here who would know if those values are in the ball park.

But my spark plug has never let me down.

You cannot use plug color to evaluate jetting when you run unleaded gas, simple as that.

14:1, or even leaner, is appropriate for true light load cruise situations, but your problem is more apt to fall into a different area than you're working. Typically, although there is a degree of overlap, needle position influences mixture between 1/4-3/4 throttle, and "cruising' takes place at less than that. the area from 1/8-1/4 throttle is more under the influence of the diameter of the upper portion of the needle.

But you could have a problem with ignition mapping. To that end, return the needle to it's original placement and try disconnecting the TPS. If that clears it up, it may be either a matter of replacing or adjusting the TPS.

what will unplugging the tps sensor do? I think i read somewhere that if you unplug it, the cdi will go to WOT spark map. is that correct? If unplugging the tps helps will it hurt anything to leave it unplugged?

I'm wondering if it isn't the tps or something spark related as even though the jetting seems to be spot on there is always this miss i am trying to figure out. Also for a built motor it doesn't run like it should and seems low on power.

I know you can pull the carb and flip it up side down to measure the float height to see if it is okay, but how high should the fuel level get when i hold the drain tube up next to the carb and open the screw? I don't want to pull the carb if i don't need to and wanted a quick way to make sure the fuel level in the bowl is okay. thanks for the help guys!

what will unplugging the tps sensor do? I think i read somewhere that if you unplug it, the cdi will go to WOT spark map. is that correct?
Yes that is correct. No harm will come to the engine, but if the system were working as it should work, you could notice a drop in fuel efficiency or in part throttle "sharpness", but no damage would be done to anything.

Don't know the answer to your float level question, but I may check both mine just for fun, and I'll let you know if I do.

Thanks for all the help guys. I unplugged my TPS and it runs great now, with no miss! I think it actually runs quite a bit better and seems much more responsive. After it quite missing i actually had to richen up the needle and still is running great.

So is this a know problem that the tps will go bad causing the timing to be way off?

The TPS controls the 3D ignition mapping.

So your TPS may not be bad, but just needs adjustment.

Your manual should tell you how to test it.

So is this a (known) problem that the tps will go bad causing the timing to be way off?

We did know about it, didn't we? :busted:

The TPS controls the 3D ignition mapping.

So your TPS may not be bad, but just needs adjustment.

Your manual should tell you how to test it.

One thing not suggested by the manual is to slowly move the TPS through its range while connected to an ohmmeter and watch that the meter moves smoothly up and down as the sensor is rotated. Sudden changes or movements indicate a bad spot in the potentiometer. An analog meter is best for this test

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