2006 YZ450F Miss/Hesitation


11 replies to this topic
  • LemonDrizzle

Posted July 01, 2011 - 04:13 PM

#1

2006 YZ450F. I'm new to 4 strokes so bear with me. When I hold the throttle steady at about 1/3-1/2 throttle and am cruising in 3rd or 4th gear there is a slight hesitation here and there that almost feels like a miss. When I really lay into the throttle it pulls like a mother and the hesitation is not there. What I'm thinking is that the jetting is off somewhere in the needle, but I'm not sure whether I am rich or lean.

  • grayracer513

Posted July 01, 2011 - 06:03 PM

#2

If the miss is irregular, you're probably lean. First try adjusting the pilot screw. Even if it's already set correctly for the idle mixture, fudge it rich just a little and see if it affects your stumble. If it does, then you probably need to switch to a needle with a step smaller upper diameter to make it richer from 1/8 to 1/4 throttle. I doubt you're really running half throttle at a cruise in 4th, so raising the needle won't really change anything.

If richening does not help, you may also have a misadjusted or defective TPS. If disconnecting the TPS clears up the miss, take a voltage reading per the manual before you do anything further to it. Adjusting them on an '06 is a real pain in the butt.

  • LemonDrizzle

Posted July 01, 2011 - 07:10 PM

#3

I'll give those suggestions a shot and see what happens tomorrow. I noticed the stumble when I first got the bike last week, but after I changed the pilot from a 42 to 45 it seemed to go away. Today I put in one of the thumb mixture screws so that may have changed something requiring me to make adjustments. I tried going about 1/4 turn richer while I was riding it and it didn't seem to make much of a difference but that may not have been enough to tell. Right now I am at 1.5 turns out so maybe I need to try going about 2 turns or more to test your theory.

You're probably right about the throttle. I was doing a test ride on the street in my neighborhood and I was probably more like 1/4-1/3 throttle. I found a thread
http://www.thumperta...699#post2881699 that describes a lean needle as a "gallop" and while I wouldn't go so far as to call what I am experiencing a gallop, it sounds really close to what I am feeling so I was also planning to play around with the needle tomorrow as well. Do you know where a guy could find a reference of some sort that shows the different needles and their dimensions? If I am reading the chart on page 7-7 of the manual correctly, NFPQ-4 would be a richer needle diameter with an equivalent clip position which would richen 1/8-1/4 throttle. Please correct me if I am wrong.

Thanks for the help, I'll report back when I have a better idea of what is happening.

Edited by LemonDrizzle, July 01, 2011 - 07:34 PM.


  • Troutman

Posted July 01, 2011 - 08:05 PM

#4

I'll give those suggestions a shot and see what happens tomorrow. I noticed the stumble when I first got the bike last week, but after I changed the pilot from a 42 to 45 it seemed to go away. Today I put in one of the thumb mixture screws so that may have changed something requiring me to make adjustments. I tried going about 1/4 turn richer while I was riding it and it didn't seem to make much of a difference but that may not have been enough to tell. Right now I am at 1.5 turns out so maybe I need to try going about 2 turns or more to test your theory.

You're probably right about the throttle. I was doing a test ride on the street in my neighborhood and I was probably more like 1/4-1/3 throttle. I found a thread
http://www.thumperta...699#post2881699 that describes a lean needle as a "gallop" and while I wouldn't go so far as to call what I am experiencing a gallop, it sounds really close to what I am feeling so I was also planning to play around with the needle tomorrow as well. Do you know where a guy could find a reference of some sort that shows the different needles and their dimensions? If I am reading the chart on page 7-7 of the manual correctly, NFPQ-4 would be a richer needle diameter with an equivalent clip position which would richen 1/8-1/4 throttle. Please correct me if I am wrong.

Thanks for the help, I'll report back when I have a better idea of what is happening.


Definitely disconnect the TPS, that clears up the 1/4 turn throttle hesitation/miss immediately. I had my 06 for three years before I did that and I should have done it three years earlier. It was perfect at 1/4 throttle after that.

  • LemonDrizzle

Posted July 02, 2011 - 04:48 AM

#5

Definitely disconnect the TPS, that clears up the 1/4 turn throttle hesitation/miss immediately. I had my 06 for three years before I did that and I should have done it three years earlier. It was perfect at 1/4 throttle after that.


I am going to check the TPS for sure, but I don't know that I would want to leave it disconnected permanently. I know that people do that, but I feel like if Yamaha put it there then they must have had a good reason so I would like to have mine working properly.

  • grayracer513

Posted July 02, 2011 - 07:13 AM

#6

You're probably right about the throttle. I was doing a test ride on the street in my neighborhood and I was probably more like 1/4-1/3 throttle. I found a thread
http://www.thumperta...699#post2881699 that describes a lean needle as a "gallop" and while I wouldn't go so far as to call what I am experiencing a gallop, it sounds really close to what I am feeling so I was also planning to play around with the needle tomorrow as well. Do you know where a guy could find a reference of some sort that shows the different needles and their dimensions? If I am reading the chart on page 7-7 of the manual correctly, NFPQ-4 would be a richer needle diameter with an equivalent clip position which would richen 1/8-1/4 throttle. Please correct me if I am wrong.

Lean symptoms tend to be irregular, and are often more of a "surge" type of miss, where it doesn't so much misfire as "go soft" for a second and then come back (a little like running out of gas). "Gallop" is kind of like that, I suppose, but it suggests a regular rhythm the a lean needle may not have. Lean conditions can be accompanied by an occasional pop out the pipe while running.

You are correct about the needle except that the NFPQ is only a half step richer at light throttle. I would go to an NFPP.

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  • LemonDrizzle

Posted July 02, 2011 - 01:03 PM

#7

If the miss is irregular, you're probably lean. First try adjusting the pilot screw. Even if it's already set correctly for the idle mixture, fudge it rich just a little and see if it affects your stumble. If it does, then you probably need to switch to a needle with a step smaller upper diameter to make it richer from 1/8 to 1/4 throttle. I doubt you're really running half throttle at a cruise in 4th, so raising the needle won't really change anything.

If richening does not help, you may also have a misadjusted or defective TPS. If disconnecting the TPS clears up the miss, take a voltage reading per the manual before you do anything further to it. Adjusting them on an '06 is a real pain in the butt.


I just got done doing a bunch of the testing that you mentioned. First I tried richening the mixture screw, and I had to go all the way out from 1.5 to 3.5 turns out until it was noticeably better. At this point it was better but it was still there just a much smoother miss if that makes any sense. Next, I tried raising the needle with the mixture screw back at 1.5 turns and that made no difference at all, about like you said.

I disconnected the TPS and rode the bike and didn't really notice anything different. Then I went through all of the test procedures in the manual and everything was in spec except for one thing. When I checked the TPS coil variable resistance it would only max out at 3.75K ohms. The book is calling for 4-6K ohms. When I checked the variable resistance I did a slow roll on the throttle and everything seemed to react as one would expect. Other than that, all resistances and voltages were about right in the middle of their ranges.

TPS Coil - 4.75K
TPS Variable - 750 ohms (Full Closed with idle still set) - 3.75K (Full Open)
TPS Output Voltage - .65V (Alignment)
TPS Input Voltage - 4.99V

I think I'm sold on the idea of putting a richer diameter needle in at this point so I am going to order the NFPP and see what happens unless you suggest otherwise.

  • GreenHornet450

Posted July 02, 2011 - 01:14 PM

#8

Try a larger PJ first. Your PJ test indicates you need to go larger. Remember 1 step at a time.

  • LemonDrizzle

Posted July 02, 2011 - 01:25 PM

#9

Try a larger PJ first. Your PJ test indicates you need to go larger. Remember 1 step at a time.


I think the pilot is ok. It's highest point of idle with the 45 PJ that's in it is 1.25 and I am running it at 1.5. At 3.5 turns out, which is max for an FCR carb I think (might be 3 turns), the bike wouldn't even run unless I kept it off idle. At 1.5 turns out with the 45 PJ that's in it, it idles fantastic and there is very minimal popping on decel. What I was trying to do by turning it way out was to fake a slightly richer needle diameter to see if my hesitation went away, and I think the fake might have been a success.

  • grayracer513

Posted July 02, 2011 - 01:42 PM

#10

I think you're on the right track.

  • YZ450Rider

Posted July 22, 2011 - 06:26 AM

#11

I know I have posted the same reply on many other threads over and over....

I thought the same thing when people suggested Pilot Jet to me. I thought, "There is no way that is the problem. I blew air threw it and it is clear... RIGHT?"

Make sure your Pilot Jet is physically clear. Remove the jet and look through the tiny hole inside the jet itself. If you can't see through it, there's your answer.

A clogged Pilot Jet will create HAVOC in these modern 4 stroke racing bikes.

That is the simplest thing to check / fix.

If you run pump gas in it and do not empty the fuel out of the carb when you park the bike, there is a chance that the ethanol-based pump gas is evaporating and then the residue is clogging the pilot jet.

It happened to me on my 04 YZ250F and I just about tore the motor apart trying to find the problem. All it was was a clogged Pilot Jet...

  • grayracer513

Posted July 22, 2011 - 07:08 AM

#12

If you run pump gas in it and do not empty the fuel out of the carb when you park the bike, there is a chance that the ethanol-based pump gas is evaporating and then the residue is clogging the pilot jet.

The phenomena has little or nothing to do with ethanol content. Gasolines of all different blends have been doing that since engines were invented. Race gas is no exception, either. In fact, VP's U4 was notorious for turning into a thick, crusty gel if left in the system, and in just a few days, at that.

The problem sets in when the fuel system is left wet and allowed to evaporate dry over time. If it's either kept wet all the time, or drained and stored dry, it's generally not an issue.





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