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Discussion Starter · #1 · (Edited)
Okay, I have a doozie here.. I'm hoping that a.) someone has heard of or had this happen to them, and b.) I can explain it properly so that a. is true.

My bike is a 2007 Ninja 500.

I had a BUNCH of work done on my bike within the past 6 months.. long story short, lady backs into it, dings it up real good (cosmetic scratches only, nothing mechanical damaged), i use the insurance $ to fix it up differently than insurance intended.. I replaced the damaged stock exhaust with a Muzzy. Had a jet kit installed. New spark plugs, new chain, new K&N air filter, had the valve clearance checked. New cush bearing thing (forget the technical term), new rear wheel bearings, new tires. Cables lubed. Umm.. I think that's it.

So here's my problem.

Upon reception of my new hotness bike, it's had a chronic and predictable problem that the bike shop has yet to properly troubleshoot.. and I know for a fact this problem did not exist prior to their work. Upon acceleration, the engine hesitates. More specifically, specific levels of acceleration cause what feels like a 'muddying up' of the gas/ignition process, causing stuttering and what I affectionately call "spluttering".

I'll try to explain further, as I'm not a mechanic, so forgive me if I don't provide enough or the wrong details.

So in the morning, I start up the bike. I choke it out and get the idle up high. No spluttering. I let it sit for about 60-120 seconds like that until the idle evens out, then I drop it down to raw idle. I let it sit for another minute or two, then I take off. As I drive away, I can open the throttle _very_ slightly, like a grandma opening a jar of peaches, and no splutter. The moment I open it to a certain point, let's say 20%, it hesitates and starts to splutter. It will lag and at times, slow down. Kinda sounds like I have water in my gas. Or peaches. If I let off the throttle just a hair, it goes normal. I can go back and forth, and it's repeatable. It's as if there is an invisible line that I can cross that causes this problem, and it exists at any speed, in any gear, and at any temperature, but only with specific levels of throttle. I find it significant that it does not do this with any amount of choke that I apply.

If I open the throttle up to, let's say 80% and above, the spluttering ceases instantly and I really get moving. So at near-idle, it performs nominally. At near wheely, it performs as I'd expect. Anywhere in the middle, horrid.

The bike shop thinks that it's too lean, or too rich, and that this is to be expected in the colder weather (as it's sept, and beginning to chill.) It is indeed more noticable in the colder mornings, but it does not get better no matter how long I ride, or even if it warms up to 80+ in the afternoon. This is a very constant and predictable thing, it NEVER just goes away, and the performance can be so bad (if I hold the throttle in the 'dead zone') that it can sometimes strangulate the engine, and I have to start it up and ease back into it to make it recover.. like it's gasping for air, while I look around and feel like a tool on my crippled ride.

I have a hard time believing that, by installing a new exhaust and a jet kit, I am doomed to live with this performance. I understand where the gas mixture ratio seems like a fairly logical answer, but I'm doubting it now, as the mechanic has adjusted it 3-4 times and there has been no change, no improvement. If I could imagine what it looks like in the carb, it's like at certain volumes of gas, the would-be spray turns into a "splutter" of gas, instead of the atomized mist that it should be. And at higher levels, it returns to a mist and zoom, away I go. Like there's something wrong with the 'vaporizers', whatever they are called. Or maybe spark plugs? Timing? A facial pube of a mechanic permanently immortalized inside the carb needle?

Would some other thing cause this type of performance, or otherwise mislead professional automotive technicians into believing it's a gas mixture problem? Or is this really and truly a symptom of what happens when one installs a muzzy exhaust and a jet kit (not a racing-stage kit, I think it was like 0 or 1, just a standard street kit, whatever rating that is) into their ninja. Honestly, if this is how it is, then I may either request to have the jet kit removed, or else I'm going to sell the bike, because it's become embarassing and really un-fun to drive around and sound like I use vanilla pudding for fuel.

What do you all think? Any help or advice that I can throw back at the mechanics and say 'neener neener' would be GREATLY appreciated!! :thumb:
 

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"Paging Spooph and Racer X to this thread.......Paging Spooph and Racer X"

Only other thing I can think of is the airfilter. Has that been checked amongst all of this?
 

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Fuel delivery sounds like the issue to me. Because the carb has been modified, that's the first place to look. Without knowing exactly what was changed (pilot jet, needles, main jet?) and how much, I'd say the parts or adjustments are not correct.

If you pull a plug and look at the color you should get an idea if it's rich or lean. You could also warm it up and slowly bring up the RPMs while looking at the exhaust. If it's significantly rich you should see black smoke and smell gas as it stutters.

The point where you are having problems is where the carb transitions from the idle circuit (pilot jet) to the main jet. As the slide rises it pulls the needle out of the main jet until it's completely out at full throttle. That makes me think there is a different needle, or the needle position (up or down) is incorrect.

EDIT: I just noticed you said the problem goes away with adding choke. That says you are lean, and not getting enough fuel for the amount of incoming air. If the needles are adjustable, move the clip down at least 1 notch - raising the needle and allowing more fuel flow at the same throttle (slide) position.

Because it's so bad, I think I'd start by re-installing the stock parts and see how it runs.


Jay
 

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Gabe, JKV45 said exactly what I was going to say. Can you ask, or do you know what size the main and idle jets were changed to? The stock ones are 38/98. Also, did they mess with the off-idle air/fuel screw? If so, how many turns out did they set it at? I think stock is 3 or 2.5.

And no, with your modifications you can get the bike to run right, it's all perseverance...

is there any play in your throttle cable?

oh wait... I just thought of something.... I wonder if the mechanics didn't pinch your slide seals.... I did that once and the bike ran very similar to what you're describing.... Yea, I bet it's that... New slides, and pricey! But if the shop messed up, they get to replace it....
 

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I would say it it lean in the off idle to mid range. Since it runs OK on choke.Sounds like pilot jets are now to small. You need to go up one maybe two sizes. The jet kit usually only comes with main jets. Shimming the needles might help or might need to be done also. I am not formiliar with the 500.But a muzzy over the stock exhaust is going to make a big difference.

How do you like the noise from the exhaust? If you don't love it then put the stock exhaust back on . Maybe do that yourself and see if it solves your problem.
 
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