[RobVandersluis]

Hello all, hopefully someone will be able to help me out here
Got a 2004 crf450, having trouble with a hanging idle while the Tps is plugged in..
Bike runs good with it unplugged and will rev and fall back to idle, once I plug it in it will rev up but won't come back down until I unplug it again..
Anyone experience this problem? Anything helpful would e great..
Thanks, Rob

[JimDirt]

Welcome to the site !!

First ..... do you have a Honda Service or Owners Manual to have the correct readings to test the TPS ??

Has the TPS been removed or loosened/adjusted from the Original Factory Mark ?? (usually a Yellow or White Paint Mark)

Was it running fine then just started acting up ?? , or has this been a ongoing issue ??

I am assuming you just recently purchased the bike (yes/no) , did the prior owner give any history as to the bikes issues/maintenance ??

[RobVandersluis]

Yea I have a service manual and the TPS is set correctly, it was measured at 4480 ohms and the I did the multiply by .13 and .15 to get the range and I set it within this range. I believe it is aomewhwre around 600 ohms.

Yes is has been removed, here's the backstory..

Bought the bike used about 2 months ago ish, guy I bought it off of blew up the piston and didn't want to do the work to rebuild it so he stored it for a year completely torn down and that's how I bought it.. Got a new piston and a bunch of other stuff to rebuild ( piston kit and had a local shop do the head for me, new valves and all that good stuff). So he had it completely apart and in the process of cleaning the carb I removed the TPS as I didn't know at the time that it had to be set so precisely.

Got it all back together, started up 4th or 5th kick, had a coolant leak and a few other small things to fix, but never really ran perfect..

So over the last say 2 weeks I have come down to this point where I don't know what to do next..

Also, all prior owner said was that it ran great last time he had it going, which I found hard to believe as the piston had a pretty major crack in it, but what can ya do..

[JimDirt]

As far as the cracked piston goes , that would usually indicate either a defective piston when replaced or water had got in the cylinder and hydro locked (blown head gasket with prior owner) , in which case i would question the rod/crank as being damaged from the hydro locking , (you did not mention if the crank/rod was replaced) , this would not however affect the TPS , though a bad TPS "could" keep the spark advanced too much and allow the piston to crack from detonation , but usually when that happens the piston top is pitted real bad , if the TPS is changing how the bike runs (when disconnected) , i would guess there would either be a issue with the TPS or CDI/ECM , since they are what control the usage of the TPS , but generally you can disconnect a TPS and ride the bike without any noticeable issues , , all it really does is advance the ignition timing slightly at low to mid RPM and as the RPM increases it basically stops working to keep the engine from detonating as the load/RPM's increase

It is possible that the Needle Jet (the the long brass tube the Main Jet screws into) as well as the Needle itself are both worn , this would cause erratic idle , but it would not change with unplugging of the TPS ....

Question : Is it possible that you have the TPS way off from where it should be and its possibly causing your timing to be too far advanced and making your idle higher ?? , as i mentioned , the TPS ADDS advancement to the timing when functioning , so just like in a car , if you advance your distributor , it will "raise" RPM slightly as you advance , which sounds like the scenario

Have you tried slightly moving the TPS in either direction while the bike is idling to see if it makes a difference ??

[RobVandersluis]

Yes I suppose it could be possible that the TPS is that far off, I will have to try moving the TPS while the bike is running tomorrow and I'll debug that does anything.

[RobVandersluis]

So in thinking about how I'm going to fix this..

I had some trouble setting the TPS last time it, like I could install it all properly but it was hard to get in in the correct range.

Almost as if my idle was set too high or slot for adjustment on the tps didnt give enough range to turn the tps far enough to get the ohm reading lower and into the correct range. if you know what i mean..

however, i cant turn the idle down any lower or the bike wont run.. and its not like its idling overly fast, i have it set where it sounds normal, i dont have my tach yet, its still in the mail.

any new ideas?

[JimDirt]

So at a "normal" idle the bike just dies ?? , if so , i would guess the pilot jet is clogged ......or the Intake valves have closed up , either will cause the bike not to want to idle , you should be able to turn down the idle quite a bit , i run my 02 really low (around 1,000 rpm , instead of 1,600+ , though i have a heavy flywheel weight , but the 04 has a heavier flywheel than a 02 , so yours "should idle down , unless something else is preventing it

What i would do , is remove the boot (lift the subframe to expose the back of the carb) , and loosen the idle screw till the slide does not move anymore , then turn in the idle screw till the slide just starts moving again , this way you have a accurate starting point , now check your Fuel Screw , it should be about 1-1/4 open from lightly seated , use this as a starting point for adjustments , the bike "should idle at a fairly low rpm , and you should now be able to set your TPS (set the TPS without the engine running , just using Ohms) , then start it and see what it does and adjust idle and Fuel Screw from there to fine tune