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cheeseryzf

04 yz450 supermoto steady throttle hesitation

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i turned my 04 yz 450 into a street legal supermoto. at steady throttle, 1/8 to 1/2, going down the road it breaks up quite a bit. as far as the engine and exhaust it's all stock, i just replaced the piston 3 weeks ago with a stock yamaha piston, i had to make room in the air box for the biggest battery i could fit since i didn't want to buy a $500 external stator. so flipped the foam element and put it in the air box carb hole. I made some holes in the air box sides to make up for the lack of volume in the air box. Ive tried pulling the hot start and the choke when it breaks up going down the road to see if one or the other cleans it up but niether does. Ive also moved the needle clip up and down and swapped pilots and main jets with no luck. Ive heard that un plugging the tps lead can help but once in a while you loose all power. The valves are perfect. when you roll on to WOT it pulls like a 450 should. anyone have any good info?

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Try fooling with the needle position. If the miss seems irregular, it may be lean; raise the needle one notch (lower the clip). If the miss seems regular, it may be rich; try dropping it one.

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mine(2004) did this. I raised the needle and it helped. I also changed the pilot jet to one size bigger. Never got rid of it completely. My new 2008 does it as well, just not as much.

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James Dean did some research on this and told me the miss on WR's is an ignition issue with the stock CDI. My Wr250 does this too and the A/F ratio is spot on at 12.8:1.

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12.8:1? If the AFR is that low at part throttle under light loads, I'm not surprised it stutters. Using gasoline, stoichiometric AFR should be 14.7:1, plus or minus 0.1, although it can be as rich as 13.9 with a high percentage of cheap oxygenates, like MTBE, or ethanol. Full power mixtures at full throttle can go as high as 13.5-13.8 with good pump gas. 12.8 is something more for highly oxygenated fuels like U4.2.

Modern engines often run cruising mixtures as lean as 16:1 or more with no significant misfire. A carbureted thumper is likely to be happier somewhere between 14.7 to no more than 15.5 under cruise loads.

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I have jetted many bikes at this A/F and they have been happy machines. All run pump fuel. I have never had good performance or max output on a dyno running 14:1 or leaner. The 12.8:1 has been the magic number in my experience.

FYI, James Dean jet kits too, are designed for 12.8:1

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Max output at full throttle is one thing. Under that situation, the AFR should be lower than 14:1, and depending on the fuel used, it could be 12.8:1. However, WOT/max power has nothing to do with what works at mid rpm/light throttle cruise, which produces much lower charge density due to the decreased manifold pressure (higher vacuum), and an entirely different set of circumstances with respect to combustion efficiency. The AFR on an engine that runs cleanly under that condition will be much higher when read during that kind of operation.

All that said, if the needle doesn't clear it up, there is a possibility that the problem may be more related to incorrect ignition mapping at light throttle, and that could either be a matter of a defect in the TPS (or the TPS setting) or the CDI, or it may be that the OEM ignition map is just not right. My '03 always acted a little lean and popped some at a steady 6-8000 like running through the whoops until I raised the needle one click. Neither of my '06's have ever done this.

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The stutter I am referring to is below 5K, possibly as low as 3K

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You are also referring to a WR, which has an entirely different ignition system and timing map, but that's OK.

The graphs would be far easier to diagnose if they were an oscilloscope read out of the ignition secondary, instead of feed back into the dyno, which exhibits any interruption as a spike, no matter what brought it on.

In any event, bumping the needle will either improve it, or make it worse, so for most people, it's the easiest thing to try.

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Max output at full throttle is one thing. Under that situation, the AFR should be lower than 14:1, and depending on the fuel used, it could be 12.8:1. However, WOT/max power has nothing to do with what works at mid rpm/light throttle cruise, which produces much lower charge density due to the decreased manifold pressure (higher vacuum), and an entirely different set of circumstances with respect to combustion efficiency. The AFR on an engine that runs cleanly under that condition will be much higher when read during that kind of operation.

All that said, if the needle doesn't clear it up, there is a possibility that the problem may be more related to incorrect ignition mapping at light throttle, and that could either be a matter of a defect in the TPS (or the TPS setting) or the CDI, or it may be that the OEM ignition map is just not right. My '03 always acted a little lean and popped some at a steady 6-8000 like running through the whoops until I raised the needle one click. Neither of my '06's have ever done this.

Hey Gray, i think your on to something with the TPS. Eddie over in the jetting forum says Yamahas are notorious for "surging" at steady throttle. He recommends just disconnecting the TPS. The other thing i'm not quite clear on is filling the airbox with a battery? That doesn't sound very proper. I wouldn't put anything in the airbox and drill holes to compensate????? Am i missing something?

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...The other thing i'm not quite clear on is filling the airbox with a battery? That doesn't sound very proper. I wouldn't put anything in the airbox and drill holes to compensate????? Am i missing something?
I'd have to see what's been done there to judge it.

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i've moved the needle with no real difference in the hesitation. i alson increased the pilot one size and the gremlin lives on. i heard something about unplugging the TPS to cure this problem, but it also may occassionaly leave you with no power. i would unplug it if there wasnt the possibility of having to eject to live another day, if you know what i mean. anyone have any experience with this?

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it's not the cleanest setup, but i did what i had to do to get my motard a liscence plate. I had a small battery in the airbox with the filter element installed properly and the battery lasted about 45 min. so the plastic mount inside the filter came out and the filter got flipped over and covers the airbox hole to the carb and the largest battery i could fit got stuffed in the airbox. It actually had the same hesitation with the small battery that it does with the big one. i wanted to try a couple of small holes in the airbox side to see if it would clean up my running issue if it came from a severe lack of airbox volume. it didn't, so now i classify them as speed holes.

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I a little shocked I got bad gas from someone, the reason?? Too many posts!!! Pretty petty and childish. Sorry for trying to be of help.

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I a little shocked I got bad gas from someone, the reason?? Too many posts!!! Pretty petty and childish. Sorry for trying to be of help.
To the individual who gassed Wm1, let me say first that I know exactly who you are, just for starters.

To continue, I'd like to say that I see no reason for your having done this, or at least no valid one. I can think of a couple you might have used. The first, the one you gave, "too many posts", is ludicrous. It might be your opinion, but I would think that someone such as myself, with 50% more posts than William has would have been notified by you some time ago that I had exceeded your limit. So, I'm thinking that's not really it.

Then, it occurs to me that you might be upset that he had the temerity to argue with me about something. I really hope that's not it. For one thing, I can take care of myself in any debate I enter into, and for another, one of the points of having a discussion forum is to have discussions. Viewpoints differ, and as long as the exchange remains civil, it's usually useful to compare the merits of opposing arguments. If he or anyone else thinks that I, or anyone else, is wrong about anything, he's free to say so, particularly if he can offer some support for his contention.

Then again, maybe you just don't like him. Maybe it doesn't even have anything to do with anything he's posted here in this forum. In that case, I have this to say; it's your opinion, and you're entitled to it, but you might notice by his rep that it isn't widely shared. I imagine now that you won't be too happy with me either. Be that as it may. Your bad gas point won't hurt him in the end.

But know this: I'm not going to put up with the kind of abuses of the rep system that have occurred in other forums. If I see a pattern of any member dumping on somebody just because they have a different take on things, I'll hand out infractions for it. The rep system allows you to label as troublemakers and misfits those who truly are without their knowing who did it, so they can't retaliate against you for calling a jerk a jerk. It also allows you to unfairly attack people whose only offense is that they disagree with you, or worse yet, told you were wrong when you actually were. You're not entirely as anonymous as you might think.

Word.

P.S.: Remember that publicly complaining about a moderator's actions in the course of his job is a 5 point infraction, and an automatic temporary ban. Anyone who has a disagreement with this is advised to PM me or my boss.

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Wow Gray, I am taken aback! I certainly appreciate your comments and I certainly did not expect such a strong statement. I do take notice of your choice of words 'argument' as I (and I hope everyone) tries to share their knowledge. Some right, some wrong. I like debate or discussion better. I am not an arguer. :thumbsup:

I also do my best to admit or agree when I have mispoken. In that end, you are absoutely correct, the James Dean stuff is WR specific and not YZ. LOL, you've corrected me a few times, in a reasonble manner. LOL, I assure you, your number of corrections will diminsh over time as I 'suck the knowledge from you'. :rolleyes:

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I do take notice of your choice of words 'argument' as I (and I hope everyone) tries to share their knowledge. Some right, some wrong. I like debate or discussion better. I am not an arguer. :thumbsup:

Used in the non-pejorative sense as:

2 a reason or set of reasons given with the aim of persuading others that an action or idea is right or wrong

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