2018 YZ450F Died and won’t start help!!!

AZIMM84
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AZIMM84
Edited Date/Time 12/28/2021 3:47pm
I bought a 2018 YZ450F 54 total hours second hand, guy started for me ran great, didn’t ride it because it was dark outside. Seemed to run solid. Got it home, unloaded it started it, idled for about 45 seconds. I jumped on went to go and killed it…. Started right back up killed it again??? Started it again let it idle and it kinda fizzzled out like it was out of gas… went to start it and killed the battery. Put it on the charger and notice the starter clutch was slipping… starter clutch ended up going out and would not start back up. I got a few backfires but nothing…

$300 later I replaced the starter clutch. New battery, Cranks and cranks and cranks w t f …..

I can hear the fuel pump prime… pulled plug and it’s got great spark…. Sprayed a little starting fluid in air box and NOTHING …. What how why grrr….
Couple back fires but nothing. It ran and idled perfect…


Checked valves they were in spec almost as if recently done…

Checked timing to see if it jumped… it’s dead on perfect…

Checked compression scratch that you can’t
Leak down test within 5-10% so that’s good.



Stumped… I don’t get it . No codes on the app… I’m lost.. I feel like I got burned and out $5000
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Racer142
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Racer142 11/20/2021 4:49pm
11/20/2021 4:49pm
Sounds like something simple that you over looked honestly. You said you hear the pump prime but I'll be honest I can't remember hearing mine but I believe you. If that's the case and you have spark abs compression I'd start checking electrical connections. Especially to the injector. Maybe your right and they recently did valves and didn't plug something back in all the way
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AZIMM84
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AZIMM84 11/20/2021 8:28pm
11/20/2021 8:28pm
I did notice my battery drops to 10v when cranking, could this somehow cause it not to start? Still cranks fast…
AZIMM84
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AZIMM84 11/21/2021 7:58am
11/21/2021 7:58am
Not yet

I did check fuel pump and got 50 ish psi while cranking, I checked voltage at Injector and only getting 0.9v I think??? What is the voltage supposed to be at the Injector while cranking ?

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watson90
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watson90 11/21/2021 8:19am
11/21/2021 8:19am
I would try a new spark plug anyway and rule it out
mattyhamz2 11/21/2021 9:17am
11/21/2021 9:17am
watson90 wrote:
I would try a new spark plug anyway and rule it out
Cheap insurance so I agree.
Family friend bought a new plug for his 17 CRF450, put it in and wouldn’t fire up. Put the old plug back in and it fired up immediately. NGK sent him a new plug and all was fine.
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AZIMM84
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AZIMM84 11/21/2021 10:08am
11/21/2021 10:08am
Update replaced spark plug tried two of them.
With the injector out of throttle body hooked up it sprays a fine mist of fuel so apparently working?

Jumping the bike with my truck it almost is running, but still the speed of the starter won’t react to throttle input, pipe gets hot etc

Tried to bump start it down a hill it basically runs at idle speed but soon as throttle input it dies out won’t actually rev at anything past the speed of what the starter would turn the motor over at…

I give up !

Occasional bang and pops when trying to start it regular… acts like it is out of time I triple checked everything and so did a tech
harescrambled 11/21/2021 5:10pm
11/21/2021 5:10pm Edited Date/Time 11/21/2021 5:10pm
AZIMM84 wrote:
Update replaced spark plug tried two of them. With the injector out of throttle body hooked up it sprays a fine mist of fuel so apparently...
Update replaced spark plug tried two of them.
With the injector out of throttle body hooked up it sprays a fine mist of fuel so apparently working?

Jumping the bike with my truck it almost is running, but still the speed of the starter won’t react to throttle input, pipe gets hot etc

Tried to bump start it down a hill it basically runs at idle speed but soon as throttle input it dies out won’t actually rev at anything past the speed of what the starter would turn the motor over at…

I give up !

Occasional bang and pops when trying to start it regular… acts like it is out of time I triple checked everything and so did a tech
So you've gotten it to idle. How how is the pipe getting? If it's getting red hot your cam timing is off. Are the marks property aligned on both cams? If so, did you pull the flywheel and see if the woodruff key is intact? If it's not, the flywheel has turned on the crank. The marks would still line up, but the engine would be out of time
AZIMM84
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AZIMM84 11/21/2021 6:05pm
11/21/2021 6:05pm
When I say idle, it only is “running if that” at the speed the starter turns the motor, pipe is hot to touch but not glowing no it’s only for a briefs few seconds, if I bump start it kinda same thing it runs/turns motor over and creates enough fire to get warm at the speed of the engine being turned over. Dies out / doesn’t respond to throttle input.

And no I did not check woodruff key very valid point!

Timing is dead on checked 100x

I think I’m going to bite the bullet and take to Yamaha, I may pull cover off and see if flywheel moved though
Matt Fisher 11/21/2021 7:26pm
11/21/2021 7:26pm
A bad TPS can cause all sorts of mayhem on today's bikes...
AZIMM84
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AZIMM84 11/21/2021 7:57pm
11/21/2021 7:57pm
Wouldn’t that throw a code? Will give it a check
mx317
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mx317 11/22/2021 11:11am
11/22/2021 11:11am
If you could find someone to use his ECU, I would try that next. You might check to see if something freak happened in the muffler plugging it up. It sounds like you did all the major stuff.
mx317
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mx317 11/22/2021 11:12am
11/22/2021 11:12am
Also check to see if the butterfly is opening in the throttle body.
AZIMM84
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AZIMM84 11/22/2021 4:26pm
11/22/2021 4:26pm
exhaust is clear, butterfly opens, gonna possibly buy an ECU, I am out of things to try at this point everything OHM'd out to spec except the coil but it still has bright spark, or I am just testing it wrong....

does the 18's not have a tip over sensor?
DAG
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DAG 11/22/2021 8:19pm
11/22/2021 8:19pm
Did you check what fuel map is in it with the app tuner? Maybe reload a fresh fuel map?
AZIMM84
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AZIMM84 11/22/2021 10:39pm
11/22/2021 10:39pm
yah I have tried a few...
Timo
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Timo 11/23/2021 2:21am
11/23/2021 2:21am
Are you making sure the cold start plunger is pressed in?
charlie68
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charlie68 11/23/2021 5:02am
11/23/2021 5:02am
Has the injector been cleaned?

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AZIMM84
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AZIMM84 11/23/2021 5:15am
11/23/2021 5:15am
cold start does not make a difference, injector has been cleaned.Does not start even on starting fluid.I think I am going to take it to Yamaha at this point
mx317
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mx317 11/23/2021 5:24am
11/23/2021 5:24am
AZIMM84 wrote:
cold start does not make a difference, injector has been cleaned.Does not start even on starting fluid.I think I am going to take it to Yamaha...
cold start does not make a difference, injector has been cleaned.Does not start even on starting fluid.I think I am going to take it to Yamaha at this point
If you had not ran a leak down test, I would swear it's mechanical. A friend of mine had a KX450F and we did every check known and swapped over ignitions from another bike and he had a cracked piston.
AZIMM84
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AZIMM84 11/23/2021 5:34am
11/23/2021 5:34am
I am going to have Yamaha check it out. I feel its mechanical as well.
AZIMM84
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AZIMM84 11/23/2021 3:34pm
11/23/2021 3:34pm
They think its possibly the ECU and going to test tomorrow. Is it worth to upgrade to a Vortex if its bad?
Rider 5280
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Rider 5280 11/23/2021 5:35pm
11/23/2021 5:35pm Edited Date/Time 11/23/2021 9:50pm
I would stick with the stock Ignition/ECU given the phenomenal (in my opinion) capability of the Yamaha Power Tuner app. It's easy to use and the changes you can make are drastic at times. Given you ride a 450, I believe it's even more beneficial given you might want to dull the power or move it around by trial-and-error. With the Vortex that is faaaar more labor intensive.

Why do I recommend this? Because I have both. And while I appreciate the Vortex, no question, the Yamaha Power Tuner takes the bike and riding to a whole new level (for me) given the convenience/ease of changing settings. I've ridden 20 maps in one hour - no kidding.

Here's a potential used option (no affiliation, just an eBay search I just ran):
https://www.ebay.com/itm/2018-Yamaha-YZ450-OEM-CDI-Box-B4345-/373757414…

My 3 cents.

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Donk122
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Donk122 11/25/2021 5:05pm
11/25/2021 5:05pm
unplug the kill switch when trying to fire, rule that out.
check the two tabs on the coil, the slides wear out/fill with dirt, water etc and develop a bad, intermittent contact sometimes...
make sure the fuel line isnt kinked.. seen some guys 180 the tank to set it on the rear fender while working on it, and instead of going 180 back to zero they rotate the wrong way, go 360 and completely kink the line...
check all grounds, connectors...
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AZIMM84
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AZIMM84 12/2/2021 1:54pm
12/2/2021 1:54pm
A little update, Yamaha has the bike they said it was the ECU, got new one in and still no fire.. they removed the fuel pump and said it does not power up when connected direct to a battery.... Blows my mind since I got it to show fuel pressure, but it could have been in and out? When the bike did die when this all happened it seemed like it was out of fuel.... So now I wait again for new fuel pump assembly and see if this fixes it... fingers crossed.
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Rider 5280
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Rider 5280 12/2/2021 11:45pm
12/2/2021 11:45pm Edited Date/Time 12/2/2021 11:51pm
AZIMM84 wrote:
A little update, Yamaha has the bike they said it was the ECU, got new one in and still no fire.. they removed the fuel pump...
A little update, Yamaha has the bike they said it was the ECU, got new one in and still no fire.. they removed the fuel pump and said it does not power up when connected direct to a battery.... Blows my mind since I got it to show fuel pressure, but it could have been in and out? When the bike did die when this all happened it seemed like it was out of fuel.... So now I wait again for new fuel pump assembly and see if this fixes it... fingers crossed.
Thanks for the update, please keep us posted.

This is a pesky situation, sorry to hear it. Every troubleshooting step is 1 step closer to it running perfect, but dayuuum. Buys a nice bike, bam ... won't run. Total bummer.
Chippy
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Chippy 12/3/2021 7:36am
12/3/2021 7:36am
Did the previous owner say much? That's crazy it started right before you bought it and now this. Wonder what would have happened if you rode it first. How does the old fuel pump look?
AZIMM84
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AZIMM84 12/3/2021 7:50am
12/3/2021 7:50am
Guy I got it from said he got it on trade one of those deals, Fuel pump is OE for sure, but it did test here maybe it was intermittent, I am not convinced it will run with a  new one but we will see...
btroxler
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btroxler 12/3/2021 9:52am
12/3/2021 9:52am
Take it to a Yamaha dealership and let them hook it up to the computer, this comp does way more than your app will.

Example. I had one that would only bump start, come to find out it was the water temperature sensor connection was NG and when you hooked it up to the computer it read -25 degrees C so it was causing it to dump a lot of fuel in and you could not turn it over fast enough to get it to start, but if you pulled it and bump started in 2nd or 3rd gear and it would fire up.
Moto520
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Moto520 12/3/2021 4:25pm
12/3/2021 4:25pm
We are all pulling for you……keep the updates coming. This has to be so frustrating but those are very low hours. It’s going to be something simple I’ll bet. I’m at 90 hours on my yz450f and it has been the most reliable bike I’ve ever owned. I still haven’t so much as checked the top end or anything else and it runs perfect.

You’ll get this and the bike will be awesome.
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