YZ450F Hard to Start


45 replies to this topic
  • joeprunc

Posted March 22, 2011 - 11:45 AM

#21

I put an aftermarket air/fuel screw in, and I thought it was the culprit of the hard starts, so I went back to stock (at least I knew I was at 1 3/4 turns out), unfortunately it didn't improve much. I plan on getting it starting properly, then fiddling with the aftermarket air/fuel screw.

If his bike started first or second kick before changing the oil, I don't think the valves would be an issue, but it is always worth a check.

  • wanawakeboard

Posted March 22, 2011 - 12:23 PM

#22

Any update wags?

  • wags450

Posted March 22, 2011 - 12:29 PM

#23

Well after feeding my face with some carne asada tacos and a beer i decided it was time to work.

I found 2 things that I believe are causing this.

1) it seems that the screw that tightens up the connection from the airbox to the carb was loose. I have never taken that apart so Im not sure how it came loose.

2) fuel screw was out 3 1/2 turns. Dont know if that was me or if it was the guy before but thats where it was. I got it back to about 1 3/4 and 2 turns

Bike took 3 kicks but no throttle (huge improvement from 8-10). I think it was a combo of the 2 things letting to much air in (bad seal until it got hot and sealed up) and fuel screw.

I also tried to wipe the filter with a paper towel as suggested but there wasnt much to come off of it. I am going to go try it in a little bit to see if its the same

  • wanawakeboard

Posted March 22, 2011 - 01:35 PM

#24

SWEET! Im glad you seem to have figured it out, If that pilot was meant to be 3.5 turns out You need a bigger pilot jet, but if it is running better then I think you found the trouble, perhaps the guy that owned it before tried to compensate for the loose air box collar (letting air in) by turning the fuel screw out (allows more fuel) Id be worried about how much dirt got past the air filter, but Not much you can do but move forward... :thumbsup:
P.S Damn I want some carne asada now...

  • wags450

Posted March 22, 2011 - 01:45 PM

#25

Im not too worried about the dirt the tunnel is really clean and there doesnt seem to be anything in the carb. I am assuming that it was big enough to let air in at the start but not after it heated up and everything expanded closing off the gap.

The carne asada man that was good. I dont know where your at but if your out in the OC somewhere I would say pick up some Tauqeria De Anda man is it good. Made a special 20 minute trip with a friend for a tube and a taco.

  • joeprunc

Posted March 22, 2011 - 01:46 PM

#26

I'm glad you figured that out, but that isn't what I want to hear....I double checked that connection as well as the carb to head boot several times and they are tight.

Looks like UPS isn't going to deliver my package today due to weather issues, probably issues getting over hwy 80 (even though I paid the extra coin for 2-day). Maybe I will try fiddling with my air fuel screw. I'm hoping that the pilot jet just varnished over during the several weeks when the bike was apart.

I'd keep an eye on both of the connecting boots to the carb. I remember reading a post about those being weak joints, some people use zipties to help keep them tight.

  • wags450

Posted March 22, 2011 - 01:53 PM

#27

I was talking to my buddy right now and he brought up something interesting which I dont know if it applies to this but here it goes.

He had an iridium spark plug in his yz250f everything was awesome. He needed one in a pinch and tossed a plain old fashioned one in and the bike was harder to start and popped more. Once he put in a new iridium plug everything was back to normal.

Dont know if thats a coincidence or him smoking tooo much weed but thats what hes claiming.

  • ttr250dude

Posted March 22, 2011 - 03:08 PM

#28

I was talking to my buddy right now and he brought up something interesting which I dont know if it applies to this but here it goes.

He had an iridium spark plug in his yz250f everything was awesome. He needed one in a pinch and tossed a plain old fashioned one in and the bike was harder to start and popped more. Once he put in a new iridium plug everything was back to normal.

Dont know if thats a coincidence or him smoking tooo much weed but thats what hes claiming.


He's right. When i had a basic plug it started alright but took 4-6 kicks to start. I put a iridium plug in and it starts 1-2 kick wether its hot or cold.

  • wanawakeboard

Posted March 22, 2011 - 05:54 PM

#29

Im not too worried about the dirt the tunnel is really clean and there doesnt seem to be anything in the carb. I am assuming that it was big enough to let air in at the start but not after it heated up and everything expanded closing off the gap.

The carne asada man that was good. I dont know where your at but if your out in the OC somewhere I would say pick up some Tauqeria De Anda man is it good. Made a special 20 minute trip with a friend for a tube and a taco.


OC? where is that? Im in the CV central valley...lol, actually up by sonora in a town called copperoplolis, dont tempt me man Ill show up...lol

  • joeprunc

Posted March 22, 2011 - 07:24 PM

#30

OC? where is that? Im in the CV central valley...lol, actually up by sonora in a town called copperoplolis, dont tempt me man Ill show up...lol


Copperoplolis ehhh....we were driving down hwy 4 from Angels Camp to Discovery Bay Sunday morning and boy were you guys getting hammered with rain. Some of the ranches looked like they had class 4 rivers flowing through them. Hope everyone faired alright.

Back to the topic. I didn't have much time tonight, but I pulled the air filter off and tried kicking....still several kicks, so no improvement there. But I got thinking about Wags cure. Maybe my boot is worn or not sealing properly. I was thinking of maybe carefully wrapping the carburetor to box connection with electrical tape to see if it helped seal...or I guess I can get it started, spray some carb cleaner at those joints and see if the RPMs increase or not.

I did pick up a new plug (the Iridium had to be ordered, but I may do that down the road). I think I'm going to wait for UPS to come and change the pilot jet before doing much more.

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  • wanawakeboard

Posted March 22, 2011 - 07:51 PM

#31

Yea Joe its been quite an adventure up here Raining for DAYS! today was nice but I needed to take the time to do some yard work before the damn rain shows up again tomorrow. Man I am just freaking out to go ride, but Cleaning layers of mud off 4 bikes does not appeal to me. Lets see what we can figure out on your bike, Irridium plug will help out made a big difference On my 450, You said you took off the air filter and it made no difference, Id suggest putting it back on and replacing the snorkel if you have removed it. It will help with the stock (small pilot) Your right to check for an air leak, but In truth a bigger pilot might help. Your very sure on those valves right? not too tight?

  • skull1971

Posted March 23, 2011 - 04:44 AM

#32

Anyone have the part number for the Iridium plug? I've just been using what the manual called for, CR8E, or something like that. Didn't know there was another plug.

  • QuietFlight

Posted March 23, 2011 - 05:05 AM

#33

It is just CR8EIX

IX = iridium designation for NGK

I go grab one from Advance Discount Auto Parts before every ride lol.

Edited by QuietFlight, March 23, 2011 - 05:06 AM.
left something out.


  • wags450

Posted March 23, 2011 - 05:47 AM

#34

OC? where is that? Im in the CV central valley...lol, actually up by sonora in a town called copperoplolis, dont tempt me man Ill show up...lol


Haha OC is Orange county the place im talking about is off of the 57 and 91 freeways. Im up in LA county in the Angeles National Forest so its a drive for me to get down there but it just so happens UNI and EMPI are right down the street. Pick up some tacos and parts for my buggy and bike.

  • joeprunc

Posted March 23, 2011 - 08:04 AM

#35

Anyone have the part number for the Iridium plug? I've just been using what the manual called for, CR8E, or something like that. Didn't know there was another plug.


None of the autoparts stores here had the NGK CR8IX plug, they had to order them. Napa's part number is 4218 and it costs a bit over $9. I grabbed a CR8E and will see if that helps. (also fyi the IX plug gap is a little different than the E).

  • joeprunc

Posted March 23, 2011 - 08:50 AM

#36

Yea Joe its been quite an adventure up here Raining for DAYS! today was nice but I needed to take the time to do some yard work before the damn rain shows up again tomorrow. Man I am just freaking out to go ride, but Cleaning layers of mud off 4 bikes does not appeal to me. Lets see what we can figure out on your bike, Irridium plug will help out made a big difference On my 450, You said you took off the air filter and it made no difference, Id suggest putting it back on and replacing the snorkel if you have removed it. It will help with the stock (small pilot) Your right to check for an air leak, but In truth a bigger pilot might help. Your very sure on those valves right? not too tight?


Yup a bit more rain is coming our way, its good for the snow pack. I hope it doesn't rain to hard this weekend as we have a race at Sears Point (and our car doesn't have rain tires).

What do you mean by snorkel...the rubber boot from the air box to the carb? I do use a bit of force on that boot to get the carb out, maybe I'm developing a small crack. Also looking at it there is this small weep/vent hole at the top. I wonder if this is suppose to be a one way blow valve and maybe taking off and putting on the carb is causing it to become a two way hole. Here's a schematic diagram of the 2003 Intake.

I'm also already running a larger than stock pilot already, #45 (I think 40 was stock for my bike). I have a feeling the previous owner put a larger pilot in when he installed the PC Ti4 Exhaust.

I've checked the valves on three separate occasions hoping to find that as the issue. All five are dead on. I even was a little afraid of a leaking valve seat, and pooled quite a bit of carb cleaner in the intake & exhaust valve sections and left it for several hours, the fluid level did not decrease.

  • CrewChiefB2B

Posted March 23, 2011 - 10:00 AM

#37

i have the same bike w Dr. D full exhaust and a k&n thats all... its got a very distinct personality but i found it out and now it starts within 3 kicks everytime like clockwork... sequence of events is turn gas on, lean bike till it about overflows out carb tubes, twist to full throttle 3 times pretty snappy, choke full out, no hot start lever, and a strong leg to kick it... this works so well for me i make bets it will start first kick for who buys lunch... when cold the thing is most subborn thing ever tho even w eather.. fresh gas couldnt hurt either tho..... braaaap on

  • wanawakeboard

Posted March 23, 2011 - 10:44 AM

#38

sorry man the wr has an air tube on top of the airbox made out of rubber that guys remove to allow more air in. didnt see it on your diagram for your bike, I had an 03 yz450 but it got stolen before I really had done any work to it...

  • joeprunc

Posted March 23, 2011 - 10:56 AM

#39

Right on, it looks like the jets should show up this evening, and work looks like it might slow down for me today. Maybe I'll get a few hours of kicking with different situations to try and help diagnose the issue better. I can feel my right leg growing a little more than my left (but sure helps with my telemark turns).

I am a little suspect about that air boot, I'll probably look at that too today.

  • joeprunc

Posted March 23, 2011 - 07:52 PM

#40

I changed the pilot jet, leak jet, needle valve, and bowl gasket. It looked like the bowl gasket was pretty flat and allowed some mud/dirt to slip by the gasket. There were two little clumps on the bottom of the bowl. This helped a lot, I don't have to give it throttle anymore when starting, which was how it was in the past. It still takes quite a few kicks to get it started. But the motor sounds like it wants to turn over almost every kick, but sputters out and dies. I'm guessing its a weak spark, so that is what is next.





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