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Please help :( 07 YZ450F

11K views 22 replies 2 participants last post by  Skuddman 
#1 ·
Good Morning,Afternoon, and or Evening fellow gents/lads.

If this is the wrong section please let me know, and I apologize in advance.

Now to my dang troublesome problem. I just recently pulled apart my bike for the first time since I've owned it (about 3 years) I do a frequent Oil Change and Oil filter change, also the Air Filter. However, just recently I decided to tinker with the Carbuerator as the bike doesn't like to idle with the choke off. It has done this since I purchased it from a local dealership. I removed all the necessary components to get it removed ( Plastics, rear mounts, seat, gas tank, rear shock, and mid support frames. I got my carbuerator off, took her apart completely and cleaned it very thoroughly making sure I took all parts off before spraying it so they didn't get damaged) I got it all reassembled, placed the carb back in, hooked back up all the necessary components and then the gas tank. She fired up, however now here's the catch... It will only start with the choke on, once warm enough will start without. Below will be a list of problems now occurring:
1) They bike seems to be at a super high RPM with the choke on, and once off the lowers but the sputters and dies.
2) The exhaust starts to glow orangish/red after a very short period of time. ( I've never noticed this before.)
3) Once the choke is off and I give it gas it seems to die instantly.
Please, any idea or insight would be greatly appreciated beyond what I could express. They charge $90/hr here at the same shop I bought it from lol. And they say a minimum of 10 hrs to fix it... I'm no broke joke, but don't have $900 laying around just to drop on this. Plus the hands-on experience would be nice for future reference. Thank you again.
 
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#2 ·
Sounds like you didn't count the turns on the idle screw and air mixture screw(the little needle looking one that is brass). You have to count how many turns out was or it mixes the fuel wrong, creating a lean or rich condition. Then the idle screw is just adjusted to an idle you like. Watch a YouTube video on how to adjust a carb, very easy and a vid is easier then explaining it.

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#3 ·
I definitely did not count it. Rookie mistake. 😔 Thank you for the response jawehner1419. Are we talking about the 2 jet needles inside that carb that require a flathead to remove and reinstall? If so, as you said just YouTube how to adjust it and that should resolve my problem?

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#4 · (Edited)
No not the Jets inside the carb. If you look at the picture it is the "fuel screw" and "idle adjust"



Those are the turns you need to count. The fuel screw is generally 1 1/2 turns. As for the idle you will just have to play with it and find the right amount.

You need to have all the intake and exhaust pieces on for this process or you will get a false adjustment, so pipe, muffler, air box, air filter. Those all change the flow of air in and out of the engine. You don't have to have the plastics, seat, shock, ECT on. Just engine components.

Okay so here is my best at expailing how to adjust a carb. Put your fuel screw at 1 1/2 turns out from lightly seated because you don't want your bike running rich or lean, even for tuning. remember this is just a starting point. You want to start off with a higher idle, because later you are going to need to turn it down. The quad does not need to be running yet but does need to be warmed up. So after warming it up screw your "idle adjust" screw 3/4 or so of the way in and your idle will be fairly high during this process. At this point start the engine for the tuning process. Now you need to start playing with the fuel screw. Start unscrewing until the engine starts to fumble and sputter. Remember how many turn out this was. Now start screwing it back it. Go until is starts fumbling and spurting and getting rough. Remember how many turns in that was, so you will now have 2 numbers. now you know the range of turns where proper adjustment will be, and it should be right in the middle. 3 turns out to 1/2 turns out is the PROBABLY gonna be the range, if it isn't you need to rejet(we will go there if we need to). Put the fuel screw at the in the middle of the range you found. now you need adjust the the "fuel screw" one quarter of a turn at a time. After each turn wait 2-3 seconds to see if anything changes. If it doesn't change keep adjusting it. Once you get the highest, smoothest idle you are at the correct adjust on the fuel screw, go ahead and adjust the idle to you liking.

This is a lot easier explained on a video I would really recommend watching one so you can hear what the engine will sound like and a get a better understanding. It is the same for almost all ATVs so the ATV you find a video of should work. I will try to see if I can find the video I really liked and it explains the process very well.

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#5 · (Edited)
I found the video I really like about tuning a carb. This is actually the video that originally taught me how to tune and it does a very good job of it. It will also be a lot clearer on a four stroke because you have a more steady exhaust note unlike on a two-stroke and you will be able to hear changes better. Also your screws are in different places but other then that it is the same exact process.

How to tune an ATV - YouTube


If you follow the link you can see the video.
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#7 ·
Alrighty jawehner1419, I have an update. I have now tuned the bikes fuel jet and air jet to where the bike will idle with the choke off, and also with the exhaust piping glowing orange. However, when I go from no throttle, to giving it throttle the bike dies instantly now. However, if I slowly give it the throttle it slowly builds rpms until it is where it should be.

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#8 ·
How many turns on the mixture screw where you at? To me it sounds like your jets are lean. A lean condition makes more head then a rich condition, so the header gets red. Do you have anything at all aftermarket on it? Pipe, air filter, CDI, anything that could affect the engine.

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#9 ·
It was 2 full rotations. I have the idle adjustment 3 turns out. I started each one from a snug starting position as well. As far as aftermarket parts, I don't believe anything is aftermarket on it to be honest. Maybe the exhaust, but I don't think so.

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#11 ·
How would one go about seeing if my exhaust is aftermarket or not. Sorry, I have only ridden. Kind of pathetic since I've had this bike for 6 years now... never done the maintenence myself until now. And go figure I screw it up. I sound bizarre and I apologize.

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#16 ·
Where there any gaskets that you may have forgotten to put back in? It could be a vacuum leak causing a lean condition. Take starting fluid, brake cleaner, any cleaner in a can(not carb cleaner it will fuck the rubber and plastics)and spray it on the intake. Spray it all over. Anywhere the are two surfaces meeting past the air box. If the rpms jump, you have a vacuum leak there so remember where it is. Also take the intake boots and just squish/pinch them to show if there are any cracks. If there are that's a vacuum leak and they need replaced

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#18 ·
I want to also add. Before taking the bike apart it did not have this issue. The only problem was the idling issue because the carb was super dirty. Now the carb is cleaned, and it idles thanks to the video posted. I can get the bike to idle perfect, but once I give it gas it dies. But if I give it gas slowly and build up the rpms it can keep up.

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#21 ·
Okay. When you put the choke it creates a more rich condition because the choke cuts off air and the fuel stays the same. So when you choke it you are richening the fuel mixture. So when you don't have the choke you are probably having issues because it is running lean. Did you try using brake cleaner or starting fluid and spraying all over the intake system(past the carb) and seeing if the rpms jump? That would mean you have a vacuum leak

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