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Post by dakotafig on Aug 4, 2014 17:11:02 GMT -5
I have been following a couple of other threads, but none of them seem to turn out like mine. Probably over a year ago one day my scoot started to stutter ever 10 - 15 seconds at full throttle. It would stutter for a split second and then runs fine, then stutters for a split second and then is fine, and so on.
I have tried running with the gas cap open, I have replaced the carb, replaced the intake manifold, replaced all the vacuum tubing as well as the fuel filter. Fuel wise the only thing I haven't replaced is the fuel valve. It is adjusted where it runs fantastic, just not if you run at full throttle for more than a minute or so, then this starts.
I have never adjusted the float in the carb, but that doesn't seem to be a big issue. If I had to take a seat of the pants shot at it, it seems like it looses vacuum and the diaphragm drops momentarily, and then it recovers and runs fine for another period of time until that happens again.
Is it possible to just "run out of vacuum" at wide open throttle after a while? The strange thing is it used to run great and then suddenly this started.
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Post by alleyoop on Aug 4, 2014 17:17:15 GMT -5
It could be your diaphgram has a small air leak and would cause the needle to drop a little and the builds up enough pressure again and it raise the needle again and so son. Or due to temp changes it could be running a little to lean.
Alleyoop
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Post by tvnacman on Aug 4, 2014 17:53:34 GMT -5
what kind of air filter are you using , is it clean ?
John
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Post by shalomdawg on Aug 4, 2014 18:09:18 GMT -5
howdy, john, that sounds to me like a good question because something loose in the exhaust that momentarily blocks the exhaust or sucking the filter breifly into a blocking position in the intake does sound like it would produce those symptoms.
lotsa miles and smiles to ya
ken
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Post by dakotafig on Aug 5, 2014 8:58:51 GMT -5
I am using an uni filter, and it is brand new. I had a K/N style on there earlier but it did the same thing as it did with the stock muffler.
I thought about the diaphragm, but I have had two different carbs on. I do have REALLY bad rattling muffler syndrome. I have another muffler but haven't tried that yet because I have to get a flange cut to weld on the replacement muffler I have. I guess that brings up a good point I haven't thought of, when I first start it and go, it takes a little bit for this issue to start. Once it starts though it is non stop. Maybe like something gets hot and loose in the muffler?
FYI, my valves are adjusted great and I am running a 125 main jet.
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Post by JerryScript on Aug 5, 2014 18:05:33 GMT -5
When running WOT, you loose much of your vacuum, and vacuum is needed to keep the fuel petcock open. Some people have replaced the vacuum activated fuel petcock with a manual one to fix this issue.
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Post by alleyoop on Aug 5, 2014 19:12:13 GMT -5
FYI, my valves are adjusted great and I am running a 125 main jet.
That is your problem at WOT to fat, stock 150 about #115.
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Post by dakotafig on Aug 6, 2014 8:55:05 GMT -5
FYI, my valves are adjusted great and I am running a 125 main jet. That is your problem at WOT to fat, stock 150 about #115. Well, I had thought about that as a possibility, and it still could be hurting although if I go smaller it doesn't run as good. But, I had a 108 in there originally (as delivered from China) and it suddenly started doing the same thing even with the 108 main jet. I will try going smaller main and readjusting the carb to see what happens. One other thing I have noticed as a piece to this puzzle is if you are at mid throttle or so and quickly let it go, it will do the same stutter. It almost never stutter's going up a steep hill, and it just goes crazy stuttering if you do wide open throttle down a hill. After I think about it, I might have dropped down to a 120 main jet........ Man, old man memory has taken over....... I'll take it apart to verify and I'll look at my plug again for good measure..... |
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Post by alleyoop on Aug 6, 2014 13:29:24 GMT -5
Well you have the same motor as I do and i have it bored out to 182ccs every possible performance part on it and it takes a #38 pilot, #40 was to much fuel and the main is a 122.5 a 125 was to much fuel. It will run on a 120 but it is on the edge of Lean with a 120.
A picture of your carb area would help to see if anything is not to cool as a setup there. It should not stutter at any throttle position. If it stuttered with a 108 stock the carb was not adjusted right. Just telling you your flooding the poor thing.
Most folks do not know much about carbs and the first thing they do thinking they will get more speed out of the motor by dumping a lot of fuel in it. All that does is flood the poor thing and you actually loose power not gain any and the motor has problems running good.
Alleyoop
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Post by dakotafig on Aug 8, 2014 8:56:02 GMT -5
I understand air/fuel ratio and how that relates to engine performance. By no means am I an expert on carbs, that is for sure although I understand what and how they do what they do. I just hate tuning them.  I did pull the carb and I have a 125 main jet in there now. I would agree it is probably a touch large, but if I'm going to error I want to error on the side of rich. I ended up in this range by watching my plug. I just pulled it and this is what it looks like, which I don't think looks all that bad. Maybe I'm wrong. How do you guys thing this looks? Also, alleyoop what is the elevation where you live? Here in Kansas we are at 1800 feet. That makes a difference as well if you are at a much higher elevation. FYI my plug is an NGK CR7HIX. Thanks for everyone's input on this. I would agree it could possibly be tuned a bit better but I don't think that is related to my stuttering as it started doing that before I ever touched the stock 108 jet. As for the diaphragm, I had thought of that which is why I bought a different carb, but the issue persists so I don't believe that is it. I think I will run by the local motorcycle shop and pick up a slightly smaller jet and manual fuel valve and see what happens.  |
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Post by alleyoop on Aug 8, 2014 17:20:45 GMT -5
That is a IRIDIUM plug and the point has been broken off. You do NOT gap a IRIDIUM plug they already come gaped. You can gap them but you have to know how. Right now the gap is to wide because the point has been broken off. So get a new plug that may be why you are having troubles.
Alleyoop
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Post by dakotafig on Aug 11, 2014 15:31:48 GMT -5
I guess I should be more specific. I didn't gap this plug, I used plastic feeler gauges to verify the gap, which is exactly 0.027" as I believe it should be. Why do you say the tip is broken off? This is exactly how it looked when I bought it.
What is your opinions on the color? To me it looks like a really good color, maybe one tiny black spot where I could drop my main size a bit, but it doesn't look overly rich. Am I not looking at this right?
Thanks,
Eric.
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Post by alleyoop on Aug 11, 2014 16:46:55 GMT -5
All I use are NGK CR7HIX PLUGS and they all have a point, that one you have must be a brand new design.  I am done have a good day. Alleyoop |
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Post by dakotafig on Aug 11, 2014 16:55:38 GMT -5
Are you saying point as in like sharp needle tip or small flat tip? Here is a picture I found of the new which looks to me to be the same as mine. What about the color of the plug, how do you think that looks?  |
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Post by JerryScript on Aug 12, 2014 2:13:06 GMT -5
Notice how the picture of the iridium plug you just posted shows three sections to the center electrode? Yours looks like it's missing the tip portion.
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..BAD TO THE BONE..
