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Old October 20th, 2014, 11:16 PM   #1
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Sputters When Warmed Up

So, recent development with my '08, the bike is sputtering after the engine has thoroughly warmed up.

This started gradually, noticed it one morning on my way to work as an extremely slight sputter on the freeway, it was so slight that I was having a hard time distinguishing it from possible bumps on the road. Over the course of the next 3 or 4 days the sputtering got progressively worse after the warm up of the engine until it got bad enough to completely die roughly 1/4 mile from home while rolling to a stop sign. Luckily I was able to start her back up and get her home and she's been torn apart ever since.

First thing that came to mind was that it was a fuel delivery issue. Tried popping the gas tank thinking perhaps it was the all too common vacuum issue but this was not the case.

I also tried tearing the carbs off and peaking around inside to make sure everything was fine. She's my daily commuter so bad gas gunking up the innards was not something that I suspected, but I figured it couldn't hurt to check everything out. I inspected the seals, jets, floats, and the needle, only thing that was off strangely was a shim in one of the carbs, it was off floating around inside somehow.

After putting it back in place the bike still ran the same during a garage test. Started up and ran for the first few minutes just fine, then came all the sputtering and eventual shut down after getting up to temperature.

I put a snake camera down the valves and through the spark plug holes to check out the engine best I could and nothing looked out of the ordinary, though the piston heads did have a funny, rough texture to them which I am unsure of being normal or not.

Changed the spark plugs and still no fix. Going to change out the jets just to see if for whatever reason they need to be bigger but I'm doubting it, I've ran every day for the past year on the same jet sizes with no problems.

The bike has a little over 30,000 miles on it, Dynojet kit with needles on 2nd clip with 2 shims each, full Yoshi exhaust, snorkel delete, and removed air box with the K&N 0990 filter.

I am beginning to suspect electrical gremlins, bad ignition coils perhaps? Searched the site and various others with no real definitive direction to pursue. Any advice and/or further questions are welcome. Thanks guys.
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Old October 21st, 2014, 05:22 AM   #2
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... She's my daily commuter so bad gas gunking up the innards was not something that I suspected,
Bad gas or water in the gas can do exactly what you describe without clogging the jets.
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Old October 21st, 2014, 02:01 PM   #3
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There are definitely several possibilities that will show these symptoms. I went through similar troubles recently.
I agree with Blue though, easiest check would be to dump the tank and bowls and put fresh gas in.
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Old October 23rd, 2014, 10:05 AM   #4
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I suspect bad gas too.

But valve clearances out of spec can also cause sputtering from mistimed valve openings and closing.

How many miles are on the bike and were the valves ever adjusted?
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Old October 24th, 2014, 06:59 PM   #5
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Quote:
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The bike has a little over 30,000 miles on it, Dynojet kit with needles on 2nd clip with 2 shims each, full Yoshi exhaust, snorkel delete, and removed air box with the K&N 0990 filter.
Quote:
Originally Posted by Foxrider64 View Post
I suspect bad gas too.

But valve clearances out of spec can also cause sputtering from mistimed valve openings and closing.

How many miles are on the bike and were the valves ever adjusted?
I do the valves myself at the specified servicing intervals, this should not be the problem. The next valve clearance inspection is in about 1500 more miles.

I've been working a lot recently so have not had time to test out the bike with the new gasoline, (bike is too loud and I get home too late) but I have 3 days off coming up starting Sunday where I will be tearing through the bike to try and figure out what is going on. I'll report back my findings.
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Old October 25th, 2014, 08:50 AM   #6
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.........I am beginning to suspect electrical gremlins, bad ignition coils perhaps? Searched the site and various others with no real definitive direction to pursue. Any advice and/or further questions are welcome. Thanks guys.
I have had spark coils that completely fail after they get hot, just to resume normal work after they cool down: that is a all or nothing situation.

It seems to me a weak spark that becomes intermittent with hotter conditions (higher temp = higher pressure in the chamber = harder on sparks to jump).

I would check each connection of the ignition system (starting with the ones exposed to weather and vibrations), including switches and magnetic pick up and broken wires.

http://faq.ninja250.org/wiki/Ignition_circuit_schematic

Disconnecting one plug at a time may tell you what cylinder is missing explosions when the temperature increases; also this:

http://www.harborfreight.com/inline-...ker-69014.html
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Old October 26th, 2014, 01:28 PM   #7
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Quote:
Originally Posted by DaBlue1 View Post
Bad gas or water in the gas can do exactly what you describe without clogging the jets.
Quote:
Originally Posted by broilmebk View Post
There are definitely several possibilities that will show these symptoms. I went through similar troubles recently.
I agree with Blue though, easiest check would be to dump the tank and bowls and put fresh gas in.
Today is the first day I've been able to sit down and work on her some more.

Drained the tank entirely (took the petcock off) and drained the carbs out and then put a fresh gallon of gasoline in.

First I did a garage test, turned it on and let it run in the garage for some time. There were some minor hiccups that I noticed and it did die one time over a period of about a 20 minute test but I gave it the benefit of the doubt and shrugged them off as potential air bubbles caught in the lines and in the carbs.

The bike reached a peak water temperature of about 198 degrees Fahrenheit before the fan kept kicking on and cooling it back off. I adjusted the idle to keep the RPMs at about 3,000 just to heat it up faster. I noticed that the idle RPM wasn't quite as stable as I remember while functioning normally, it fluctuated up and down by about 100 rpm at sporadic intervals.

About an hour later I took it out for a road test. Starting temperature was about 112 degrees, I rode it for approximately 2 miles in total but it still had sputtering issues, and it died while rolling to stop signs again.

Bad gasoline as the culprit is out of the question I would say. Worth the shot though.

So what's next? Coils? Is there a way I can test those with a multimeter?
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Old October 26th, 2014, 04:51 PM   #8
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Just got done with a multimeter resistance test on both coils, the details on how to conduct this test were in the service manual.

The service manual states that the ignition coil resistance should be between 2.1 and 3.2 ohms for the primary windings, and between 10 and 16 kilo ohms for the secondary windings.

The primary windings on both of my ignition coils are at around 2.6 ohms which is just fine, however BOTH ignition coils' secondary windings are at 18.5 kilo ohms. I have a hard time believing that BOTH of them would be bad, and it's even more strange that they BOTH would be bad reading the SAME resistance value. The service manual marks the ranges with a tilde indicating that they are approximate values so I'm thinking my values, though slightly outside of this range, are okay.

Can anyone confirm that they too have a value out of the service manual's range and are operating just fine? FYI, the bolts holding the ignition coils on are 7mm, and SUCK getting off if you don't have a 7mm socket. All my sets stop at 8mm...

I will be attempting a spark test here next. I will report back with my findings again.
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Old October 26th, 2014, 05:30 PM   #9
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The spark seems just fine too, getting a strong blue arc from both plugs. Granted, the bike has long since cooled off, however I do not know how to conduct this test while the bike is still hot. Any other recommendations
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Old October 26th, 2014, 08:02 PM   #10
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Couple things I would try -

When it quits, open the float bowls and see if you get the same amount of gas out of each.

As it's starting to run poorly, add choke to see if it has any affect.

Check the vacuum line to the petcock. Manually apply vacuum to the petcock with a vacuum pump.

Check the battery voltage - before cranking, during cranking, and running at idle and 3000 RPMs.
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Old October 26th, 2014, 08:26 PM   #11
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How did the the float needles look? Mine showed signs of wear with your mileage replacing it may be a start. Have you checked your vacuum lines? If you used rubber caps for syncing the valves, the rot a whole lot faster than you would think giving way to leaks.
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Old October 26th, 2014, 09:43 PM   #12
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Couple things I would try -

When it quits, open the float bowls and see if you get the same amount of gas out of each.

As it's starting to run poorly, add choke to see if it has any affect.

Check the vacuum line to the petcock. Manually apply vacuum to the petcock with a vacuum pump.

Check the battery voltage - before cranking, during cranking, and running at idle and 3000 RPMs.
I'll give all of these a shot tomorow, thanks for the suggestions. Brilliant idea though, enrichening the mixture by use of the choke would be far simpler than changing out the jets. Completely overlooked this idea, thank you for saving me the potential work.

What makes you think it could be the petcock vacuum line though? I'll give it a shot but I'm just curious.

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How did the the float needles look? Mine showed signs of wear with your mileage replacing it may be a start. Have you checked your vacuum lines? If you used rubber caps for syncing the valves, the rot a whole lot faster than you would think giving way to leaks.
The needles looked just fine to me, I certainly didn't make note of anything out of the ordinary. What exactly did the wear on your needles look like? I never even knew wearing out needles was a thing at all, never heard of wearing out needles before.

Also can you clarify about the use of rubber caps for the valve syncing? I'm not quite sure what you mean by that. Are you referring to a valve clearance adjustment or a carburetor sync? Either way I don't ever recall using or even seeing any rubber caps.
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Old October 27th, 2014, 06:16 AM   #13
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What makes you think it could be the petcock vacuum line though? I'll give it a shot but I'm just curious.
It sounds like a fuel-flow issue to me, and if the petcock isn't opening properly or completely it may be restricting flow after a certain amount of time.

Confirming the proper amount of fuel in the floatbowls when it stops running would be another check that would tell you if you had adequate fuel flow to the carbs.

Also check all of the screens and filters in the fuel line.
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Old November 10th, 2017, 08:22 AM   #14
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Reviving this simply for closure. I ended up putting the bike away for a couple of years, and I moved from Vegas to mid Michigan. Once I finally got the bike up here, I cleaned out the carbs and changed out the stator. Magically the bike works great now! I've only put a few hundred miles on it max up here, and my wife rides it more than I do now since I picked up a CBR, but no additional problems to report. I was given the advice that the symptoms I had could be caused by a stator going bad and went with it. I don't know if the stator was the fix, or if the climate change was the fix but things are running great now! Though this is "only" a few years too late, thank you all for your help while trying to troubleshoot this!
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Old November 10th, 2017, 12:58 PM   #15
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I suspect bad gas too.

But valve clearances out of spec can also cause sputtering from mistimed valve openings and closing.

How many miles are on the bike and were the valves ever adjusted?
Yeah with over 30k on the bike, I'd highly suspect valve clearances. Also, even if the valve clearances have been done on schedule, you'll notice in the service manual that those intervals get really close together the higher the miles. This is because even with it done on time, after that many miles there's just inherent wear on the bike that'll show up a be a problem. It may be time for at least a top end overhaul.
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Old November 10th, 2017, 01:07 PM   #16
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It may be time for at least a top end overhaul.
At least it was three years ago.
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Old November 10th, 2017, 01:23 PM   #17
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Yeah with over 30k on the bike, I'd highly suspect valve clearances. Also, even if the valve clearances have been done on schedule, you'll notice in the service manual that those intervals get really close together the higher the miles. This is because even with it done on time, after that many miles there's just inherent wear on the bike that'll show up a be a problem. It may be time for at least a top end overhaul.
Never did any work to the top end to fix the issue, the next valve job is due in 1,500 miles or so, I can report back with the results form that just for the sake of providing additional information. I don't know when I'll be doing that service though, could be a while. My wife hasn't developed an iron butt yet and with our first snowfall happening today, it's probably going to be mostly parked for the next 6 months.
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Old November 10th, 2017, 01:29 PM   #18
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Nice. I saw that the issue was solved, but I thought I'd offer a bit of advice. I'm just going down the list of problems and seeing which ones I know and which ones I don't. It's also kinda my way of keeping myself current on how things work as well as offering any knowledge I can.
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