Med/high speed hiccup on 04' WR450

[BIGMatt]

Hi TT'ers,

I've got a weird problem for ya.

I have a CAN 04' WR450, stock jetting, needle raised 1 position, FMF Q muffler. Bike runs fine, maybe a little on the rich side judging from the spark plug color.

The weird problem is this:

When cruising on flat dirt roads or sections of paved road, at about 1/2 throttle in 5th gear, engine starts to have continuous short power surges every 3-5 seconds, as if the kill button was being pressed. If I accelerate it goes away untill I am back in 'cruise control mode' with the throttle held steady at one position. If I down shift it goes away. I am definatly not lugging the motor, I am typically doing 40-50 mph when this happens and just 'cruising.'

Is this a symptom of the engine 'loading up' from being too rich at too long of sustained throttle position? Or something else? If it is 'loading up', then what carb adjustment should be done?

Thanks for your help guys.

Matt

[SJMC_DON]

I have the same bike with the exact same set up and I have experienced the same thing. It really doesn't bother me because I rarely operate the bike in that mode but it is odd

Anxious to hear what others have to say.

Have you had any issues with your e-start?

[BIGMatt]

Yeah, it's not that much of a bother and I am rarely operating in this 'mode' of riding, but it is still weird and makes you think about it.

I've had my bike for about 16 months so far, only have about 1800 miles on it. No E-start problems yet, and I use it ALL the time. But square cap on the start button seems to be comming loose.

LOVE THIS BIKE!

[newthumper05]

See my thread (cutting out), I did a search for tps check it out . I think that if you unplug the tps your problem will go away.

[SJMC_DON]

Cool........... yeah those start buttons are pieces of crap.

I thought that it might have something to do with the TPS

[dbailey223]

I read a bunch about the TPS in this forum last night. Seems like the endless debate--some say unplug it to eliminate the surge, others say leave it connected (can't remember the reasons off hand).

[Brettv]

the general concensus is

unplug for road riding/commuting

plug it in for the dirt

in theory you could make switch to turn it on or off, if you ride dirt/street but you would need to shut down the bike before you switch then restart

[Matty05]

Your needle is wrong. Play around with needle position and you will find it makes

a difference. You can do what the rest of us have done and get a JD jetting kit.

I wouldn't go playing around with TPS, just get your jetting nailed.

[MotoGoalie]

I can PROMISE you this.

Your jetting is RICH as matty has alluded to.

This problem is classic for a rich needle situation, i'm absolutely sure of it. You might even be a touch rich on your main.

Here's what I would do. Lean out your needle one clip. Try er out. If it still has this surge, lean out your main one step.

I've experienced the SAME surging problem on my 03 YZ450. Go check out our YZ jetting forum as a bunch of us had this exact same sitution going on.

Don't mess with the TPS that has nothing to do with your surging. The TPS stuff is going to take you down the wrong road to fixing stuff. A touch on the lean side when jetting will not hurt these bikes. They are not two strokes.

[poffer]

Wondering if "MATTY" and "MOTOGOALI" solved their problems with leaning out on needle?? My wr450 have the same problem. I have tryed everything exept changing carb but problem is still there... Had the problem when bike was stock and now with airboxmod done, youshimura trc slip on and carb rejetted the problem is still there.

Correct me if I'm wrong but I think that cdi unit read throttle fully open all the time when TPS is dissconected. The only thing mapping the ignition besides that is rpm.

The TPS doesnt have anything to do with air/fuel mixture so I hope someone can give me a good answer why I have this problem when TPS is connected and why its gone when TPS is disconnected?

[Matty05]

trial and error. It will bog if lean and run rough as guts if rich.

I have Procircuit exhaust, open airbox and no screen in the cage.

As I said, I haven't touched TPS, as far as I know, it advances and retards spark.

[Rip Wheeler]

Matt, hey, we bought our bikes both from the same dealer at the same time. Anyway, I have the same problem also. What you are feeling is ignition timing changing as a result of the TPS (A TPS's input if for timing change only) and you are on the threshold. Inputs for timing is engine rpm and VTA or variable throttle angle which is done by the TPS. Its a resulf of high RPMs and low throttle and the timing is advancing, them coming back. Many in here just unplug the TPS and yes, it will make it go away, but you dont have optimum ignition timing and the condition in which this appears isnt long enough to sacrafice power on the rest of the ride. I usually just slowly accel, then decel, then accel. Does this make sense?

[SJMC_DON]

Maybe we'll never know but it really has no effect on my ability to have a blast and rip it up. I never experience it while racing or riding single track it's only the occasional road section to the next trail head that I notice it

I say worry less and ride more

[SJMC_DON]

Matt, hey, we bought our bikes both from the same dealer at the same time. Anyway, I have the same problem also. What you are feeling is ignition timing changing as a result of the TPS (A TPS's input if for timing change only) and you are on the threshold. Inputs for timing is engine rpm and VTA or variable throttle angle which is done by the TPS. Its a resulf of high RPMs and low throttle and the timing is advancing, them coming back. Many in here just unplug the TPS and yes, it will make it go away, but you dont have optimum ignition timing and the condition in which this appears isnt long enough to sacrafice power on the rest of the ride. I usually just slowly accel, then decel, then accel. Does this make sense?

BOOM - Nail on the head. I think my fellow Washingtonian is 100% correct!

[Brettv]

i told you it was the TPS

[Rip Wheeler]

BOOM - Nail on the head. I think my fellow Washingtonian is 100% correct!

Hey, this is one of my areas of expertise, I do it for a living. MDT = "master diagnostic technician", Toyota highest level. Ok, enough patting myself on the back ? I've heard of this symptom many times before, never felt it on my WR426, but just about 1 month ago, was in Naches and hit some asphalt (yes, I'm road plated and endorsed, but being blue, I know those guys will eventually pull me over and check me out) and I really felt this bumbling at light throttle on the WR450F, light load, higher RPM's and knew exactly what it was. We can officially put this problem to bed indefinitely!

[BIGMatt]

Hey Toyota,

Your 'diagnosis' makes total sense to me, as an engineer. Where did you learn all that TPS info about our bikes? On that note, would there be any way to 'fake' out the RPM sensor on the 'black box' to make it think the engine RPM is higher/lower than what it really is?? Is that even worth it? I too, have resorted to always, slightly changing the throttle to keep the TPS input value always changing.

I will admit that I should really take the time to jet my bike properly. But some of my rides start at 3500ft and go up to 8700 ft! I guess I can't have my cake and eat it too.

[Rip Wheeler]

Hey Toyota,

Your 'diagnosis' makes total sense to me, as an engineer. Where did you learn all that TPS info about our bikes?...

The TPS on our bikes are about the same as passenger cars. I suspect ours is like the earlier design (single pole, double throw switch (SPDT) and it operates where there is one common input and 2 other contacts, one set is closed at idle, the other set is closed at wide open throttle, and both are open anywhere in between. I doubt we have the high tech linear types by the way the timing is jumping. I suspect we are right on the edge of idle and the "everything in between" point, and then the system goes open (called idle contacts), timing advances. I don't know if the TPS is adjustable or if its just fixed. One could adjust it slightly so at cruise, the threshold would be somewhere else, but I suspect you'd sacrifice some power off of idle by raising the area in which timing advance takes place, maybe lose a little bit of that "out of the hole" grunt. I don't know of a way to trick the input sensor, I suspect it get this info from the ignition system and tampering with one, may give you a negative result on the other. I suspect adjusting the TPS would be the best way, but another area will probably suffer. Sometimes its tough to be the factory engineers design.

[poffer]

I'v tryed to adjust the tps without any luck. The owners manual says it should be adjusted between 0,58-0,78volt. I'v even tryed to adjust it both ways out of specs without that changed the area where the problem is... I'm not sure about what you meen when you say that you dont think the tps is linear but if you measure the tps ohm (resistance) you will find that at closed throttle its between 0 and 2 ohm and fully open somwhere between 4 and 6 ohm. Between fully closed and fully open the ohm value encrise. Sorry for bad english... Hope you understand what I meen

[Rip Wheeler]

... I'm not sure about what you meen when you say that you dont think the tps is linear but if you measure the tps ohm (resistance) you will find that at closed throttle its between 0 and 2 ohm and fully open somwhere between 4 and 6 ohm....

From the sounds of it, it appears to be "linear" with your voltage readings. I have never investigated the TPS or looked at the wiring diagram to see what type it was, but I'd say it is in fact, linear then. The timing is set to move at certain voltages, but wont be in relation to the voltage increases, timing will still be "stepped" at certain voltages. Usually, just off of idle, it jumps way up and different for wide open throttle. Thanks for the input poffer!