04 yz450 throttle dead spot?

17 replies to this topic
  • mxmhero

Posted October 22, 2004 - 03:22 PM


My bike is a new left over 450, Has a half hour on it just riding around the field, seems to run fine, But when i crack the throttle and hold it it stalls, if u crack but not as fast it will rev-up fine, This is my first fourstroke so i am lost, The low speed mixture screw is out 2-1/2 turns from fully seated, and has stock jetting, wanna go ride the track tomarrow but dont want to hurt the motor, sorry for the long post any help would be greatly appreciated. thx. joe

  • ovrrdrive

Posted October 22, 2004 - 03:49 PM


I'm thinking you're probably just lean, but there may an adjustment needed to the accelerator pump if jetting doesn't solve the issue.

When you slow down does it pop and backfire?

The bike should have come with a few jets. Pop the 170 main in and try going out another 1/2 turn or so on the fuel screw. That should get a little more gas into it. It's possible that when you crack the throttle ( assuming you mean open it wide open or close to wide open (3/4 to WOT)) the engine is just starving for gas and falls flat on its face. That's when a larger main will help.

Also, when you give a lot of throttle, the AP is supposed to squirt gas into the carb to make up for the split second until gas flows through the jets. If it isn't working properly you'll get a big hesitation as well. The 04's are not supposed to need the "BK mod" but you may need to fine tune the squirt.

Oh and if you think your post was long, wait until you get us started. :cry:

  • mxmhero

Posted October 22, 2004 - 04:24 PM


Its when u crack it from an idle with no load on it, If u ride it in first and slip the clutch and crack it it goes no hesitation, HMM dealer didnt give me any extra jets, it does pop a little, but not that much, I'll have to get to the shop and get some jets, tomarrow is the only day i can get to the track to ride, Im just getting back into it so i wont be beating the crap out of it, will it hurt to ride it?

  • ovrrdrive

Posted October 22, 2004 - 04:28 PM


When you say crack it, do you mean a little or a snap wide open?

If you leave the choke on does it still do it?

  • ovrrdrive

Posted October 22, 2004 - 04:30 PM


...will it hurt to ride it?

Depends on what's going on... Probably not.

  • mxmhero

Posted October 22, 2004 - 04:50 PM


Yes when u crack it from a dead idle to about 3/4 throttle, No it doesnt do it when the choke is on. So i probably need to maybe go up on the main jet like u said?

  • ovrrdrive

Posted October 22, 2004 - 04:55 PM


Actually, if it doesn't do it when the choke is on you probably need to go up on the pilot.

try another 1/2 turn out or so on the fuel screw, it may help. I wouldn't go more than 3-3 1/2 out though, it may fall out. Order yourself a spread of pilot jets and main jets. You're probably going to have to play around with both to get it right.

I'd start with a 45 pilot jet and see if it clears it up.

The problem disappearing when the choke is on tells me its a lean problem.

On second thought, I'd try going to a 45 pilot and a 168 or 170 main. Chances are good that if one is lean they both are.

I still don't know what you mean by cracking the throttle. I think of a crack as 1/4 throttle, but I'm thinking you mean alot more. The postion of the throttle in this problem is kind of important.

btw, I'm no expert in this. But I do have a good general understanding of it... :cry:

  • YZ250F_Rider

Posted October 22, 2004 - 04:59 PM


Like he said try a 1/4 or a 1/2 turn CCW on the fuel screw. That will enrichen the mix at idle so it has less tendency to bog, and it will tone down the backfiring some when you decelerate.

yamaha is notorious for sending the bikes out on the lean side of jetting. try the 170 main and see if it doesnt get a few more ponies for you.

  • ovrrdrive

Posted October 22, 2004 - 05:01 PM


Second opinions are always nice. :cry:

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  • YZ250F_Rider

Posted October 22, 2004 - 05:07 PM


but only when they agree with your own opinion. :cry:

you riding anywhere tomorrow? I am probably taking the 450 over to croom since I put the cdi in.

  • ovrrdrive

Posted October 22, 2004 - 05:11 PM


my 05 is slow...

no its not...

yes it is...

no its not...

I said it is...

I said its not...

:cry: :cry: :cry:

Btw, hows it running now?

Was that the problem for sure?

  • ovrrdrive

Posted October 22, 2004 - 05:13 PM


You edited... :cry:

I'll probably try a local area tomorrow afternoon after teeball. I think Sunday may be a boat day.

I read you were going to croom earlier. I could go Monday but the weekend is probably booked.

  • mxmhero

Posted October 22, 2004 - 05:18 PM


LOL, thx. for all your help guys, ill get the jets and try to get it better, Im use to 2 strokes so this is all new for me kinda. thx. agian.

  • YZ250F_Rider

Posted October 22, 2004 - 05:24 PM


The new cdi unit made a huge difference in throttle response. Now the revs follow the throttle, just as fast as you can twist it. It rips in the front yard now literally, I have ruts now. :cry:

boat day. ha I wish. they are talking 5 - 7' seas. No matter aint no dolphin out there anyhow.

  • CanadianKawi

Posted October 22, 2004 - 09:29 PM


My friends 04 YZF has the same problem. From idle, if you crack it wide open it will bog severly or even die. This is after about 40 hours on the bike with no problems before this. He has gone through the fuel screw from closed to 3 turns out and no difference, but hasn't changed main jet. Changed the pilot from a 45 to a 48, cleaned up somewhat. Also had mechanics look at AP and whatnot and everything checks out good there. Spark plug says that it may be a little rich, when other posts here are saying it would probably be lean. What is the stock main jet? Anyone have any other suggestions other than jetting???

  • mxmhero

Posted October 23, 2004 - 07:25 PM


Rode mine today at the track ran great, Found out my dad used my gas can and put 87 octane in it for something else, thought he put 94 in it :(so that may be why it ran like that, put 94 in it today and it ran great, I'm gonna go up on the pilot jet and main and see how it runs then go from there, just to try it out, thx. for all your help fellas.

  • Ga426owner

Posted October 24, 2004 - 05:45 AM


The JD Jetting kit will really make your throttle response a lot crisper as well as add more power to the 450's

  • Fastest1

Posted October 24, 2004 - 12:15 PM


GA426 is right, nothing but good things about JD's kits. However 4 strokes usually wont snap to life on the stand with no load. Most will actually cough and die, now under load everything changes. Ride the bike for a few rides then experiment with the jetting. :cry:

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