Posts
3009
Joined
11/3/2014
Location
Charlotte, MI
US
Edited Date/Time
7/31/2020 6:09pm
My KX250F has developed a condition where it dies unless being ridden aggressively.
When you let off the throttle it feels like there is no spark or fuel as it idles down, RPM's just fall down to a stall with the clutch pulled in and coasting.
Starts perfect when cold, idles and runs fine for 3 minutes or so. As soon as it gets warm it starts its issue.
Did a trail ride yesterday and made it 20 miles running like this(high rpm)
At this point I am thinking Spark Plug (looks good but will replace) and coil.
I have considered TPS and Air temp sensor.
On the trail ride yesterday in one section where I was headed down a steep hill it died at the top and came alive at the bottom where it flattened out..very odd. I think the tip over sensor is fine and this was a fluke.
Any other ideas? Id love to race this coming weekend so that gives me one shot at getting parts ordered.
Thanks!!
When you let off the throttle it feels like there is no spark or fuel as it idles down, RPM's just fall down to a stall with the clutch pulled in and coasting.
Starts perfect when cold, idles and runs fine for 3 minutes or so. As soon as it gets warm it starts its issue.
Did a trail ride yesterday and made it 20 miles running like this(high rpm)
At this point I am thinking Spark Plug (looks good but will replace) and coil.
I have considered TPS and Air temp sensor.
On the trail ride yesterday in one section where I was headed down a steep hill it died at the top and came alive at the bottom where it flattened out..very odd. I think the tip over sensor is fine and this was a fluke.
Any other ideas? Id love to race this coming weekend so that gives me one shot at getting parts ordered.
Thanks!!
Paw Paw
https://thumpertalk.com/forums/topic/1274436-2014-kx450f-bog-and-hesita…
My post on TT:
++++++++++++++++++++++++++++++++++
Bought a used 2014 KX450f in great shape, was vet owned with less than 20hrs on it.
Full disclaimer this is my first DFI bike (if this was a carb bike we would not be talking) and I am lost in troubleshooting this issue and hope to get some others to help lead me down many rabbit holes
Symptoms:
+++++++++++++++++++++++++++++
1- Bike starts cold or hot with out issue
2- Idles for about 10 secs and then starts to hesitate/blubbers and then dies
3- Starts right back up and repeats steps 1-2
4- If I can keep it running and start to ride everything seems fine but slowing down and having to start from low idle it blubbers and pops and I have to work the clutch and get the RPM's up to keep it running
5- this all seems to happen at 1/4" or less
6- Slowly rolling the throttle on up to 1/4 throttle is where it seems to be happening. Past a 1/4" throttle it is fine. Let the idle drop down and it hesitates/blubbers and dies
7- If I can keep it running after it hesitates/blubbers it will hit hard and will be fine if I stay on the throttle
++++++++++++++++++++++++++++++
- Running Chevron 93 gas
- New Plug and gap set
- Air Filter is clean and fresh
- No engine mods
- PC Ti-6 Full exhaust
- Black Coupler (I have tried swapping out for the other two and same issue)
UPDATED with poss Resolution?
++++++++++++++++++
What has been done:
------------------------------
- New Fuel pump Filter (Quantum)
- Cleaned Injector
- TPS Measured: .52v
- TPS Adjusted: .60v
So now rolling the throttle on the range is 0.60v ~ 3.68v
- Test with all 3 couplers
- Adjusted Valves to spec. ( we on the loose side)
- TwinAir Tank filter
- Fresh Gas93 noneth,
Damn!!!!Still at square one.
- Bike fires cold or warm without issue.
- Idols strong for a minute then the issue starts again.
- At idol anything from 0 to 1/4 throttle blubbers but once past 1/4 throttle everything is fine I take it out on the street and start to roll the throttle on and its fine then it acts like it is starving for fuel and about dies and then it hits and starts to pull hard.
As I come to a stop the idol starts to hunt and then dies. Starts right back up and idol good for about 30 sec and then starts to hunt and then dies.
*******Well I think that I have found the problem. I have to wait and test though as I am waiting for a Pro Circuit Backfire Screen Eliminator Kit.
So what I found was that when I put the harness back and mounted everything that the vehicle down sensor bracket was mounted incorrectly. (Backwards) Instead of facing out to the left side of the bike was mounted facing to the right side
The 2- marks on opposing side showing UPPPER with the arrow were actually at the 12 and 6 position. Reviewed the service manual and mounted the bracket correctly and this moved the sensor back above the CDI and now the 2-UPPER marks are at 3 and 9 with the arrow pointing to 12 o'clock in stead of 9 o'clock.
You are not getting full range of the TPS. It should be from about .5 volt at fully closed position to about 5 volts at WOT. There seems to be an issue there. I suggest setting it at .62 at fully closed position and then retesting the WOT voltage to see if it gets better.
Fuel pressure could be low.
A faulty or dirty injector could also be an issue.
Paw Paw
If it works when its cold wouldn't it work when its warm? Sensors are typically a work/dont work in my limited experience.
Would buying an new sensor be a better idea?
The Shop
Free shipping: VITALMX
Luxon 4-Post Bar Mounts
$189.95 - $239.95
DeCal Works Huge Plastic Inventory of UFO and Polisport kits.
I really thing it is a fuel pump/pressure issue, but I may be wrong as well. I have seen new pumps be bad . The fuel pressure and fuel delivery need to be checked all the way from the pump through the injector.
Paw Paw
I questioned this last time I read your post about the subject a year or so ago, but don't remember reading your reply (Paw).
In my experience on KX250F's, at wide open throttle the TPS value should be around 3.6v.
What are you using to produce the 5volt testing power?
Have to tried to adjust the top end voltage to see what you get at closed throttle?
Remember that all the TPS does is supply voltage to the computer so the fuel supply will be correct for the throttle opening. It is nothing more than a potentiometer.
Like I said, this may not be the issue and I am only offering help for what ever it is worth.
Paw Paw
Before I cleaned the plugs I rode the bike around the yard for 6 minutes before it started dyeing when letting off the throttle. Seems the fuel system is delivering plenty of fuel at slow speeds and fast speeds until the bike gets hot. I will give it another test tomorrow.
Exactly how do I test the TPS sensor? I tried using my Fluke multimeter but couldn't get any value from the three pins in the male pins in the plug. I do not have the manual to the bike either. Thank you for all the help, I greatly appreciate it.
To anyone in the future: Clean your connections!!!!!!!!
Post a reply to: 2018 KX250F dies at low RPM