07 s250 Strange problem fuel or spark related

[ifican]

The sounds and loss of power i have read others have but not really the same problem. When cold scooter runs up to 85 no issues. When warm however only gets to 70ish and goes no more, when this occurs it also makes a strange internal fluttering sound. Sounds like the muffler is partially clogged. Acts 100% normal all other times and speeds. Warm from dead stop, acceleration spot on, any other speed or other condition fine. Only at highway speeds once warm does it make that sound and it makes it every time. As soon as speed drops or let off throttle sound goes away. Get on the throttle again and right about 70 right back. Picked up with 4600 miles on it, has 15.5k as of today. Belt has about 4k on it, has new plug, ignition coil and fresh oil (both). I have heard rumblings of cdi but agree as most cdi's arnt usually intermittent they either work or dont. Though i have had ecms on cars act funky when hot. Looking for input as its driving me crazy, stay 65mph or less and it runs like a champ. Only issue with that is 65 mph around here and youll get run over.

[ifican]

Ok changed title because i am a little closer, figured if i waited long enough something would happen. Well new symptom, Pretty much from the time i start up when i go to accelerate (roll throttle alittle or all the way), will slowly accelerate for 12mph or so then it takes off. I am really leaning towards fuel so i put in a nice quantity of seafoam yesterday and we will see how that goes over the next half a tank or so. It did do one really weird thing. yesterday after acceleration to highway speed hit a pocket of traffic slowed to 25-30 while splitting lanes. When traffic opened back up would only do about 50mph wouldnt go, same feeling as from my previous post but just no faster. Pulled of freeway put on stand, gassed on it, turned off and back on no luck. Still supper bogged down and wouldnt go. While limping back home, started same behavior as no oomph from start then takes off about 15mph.

[Punk052]

Check your vacuum lines on the carb and the diaphragm on the top of the carb for holes or tears. Sounds like its not opening up the carb all the way and your air fuel ratio is off.

[ifican]

sorry about delay work has been killing me. Havent gotten around to checking yet but symptoms are becoming more regular and hopefully more telling. What its now doing is most of the time slowly accelerating to around 20 then going strong but more and more will only slowly accelerate to 40ish and go now more, just no real power. If going up really step hill will go up it but never exceeding 10 mph. On way home from work tonight, 75 on highway whole way then once got off highway (slow for offramp exit) would never get above about 40. Its about 1.5 miles from exit to home with several stop signs. No real power, acts like it wants to go but nada. Hopefully will get some time in next few days to dig into it some but otherwise looking for ideas.

one other thing, put on  stand when got home and let idle a bit. Lightly opened and closed throttle but rpms stayed up and spun rear tire, higher rpm then fast idle when its cold.

[zombie]

+1 for Punk's post. Ethanol in fuel swells the rubber diaphragm untill it does not respond to throttle.

Just to eliminate one big issue I would do a compression test, and a vacuum test. If you need help w/ these just ask.

[ifican]

compression is good, may be down alittle from age but i have owned plenty of bikes in my time that had compression issues and this is not one of them. I will definitely look into vacuum and carb issues. Hopefully will get a chance within the next week to look, will post once i get a chance to look and see what i find. Thx for the input......

[zombie]

You're welcome. Most often you will find it yourself but throwing ideas out there helps.

[Restrictor Plate]

A few things you've written bring to mind some things I've been going through:

Muffler noise - My muffler has about 20,000 km on it, and is making some noises. Normal running, it sounds normal at this point. Back off the throttle, and there's some minor popping. And when riding around 60 mph and greater, I get a sound out of it best described as the jangles of a tambourine fluttering. (Helps to be wearing an open-ear helmet or no helmet to hear it.) I think it is an internal baffle that has let loose. I will eventually be replacing my muffler. (They are not repairable from a practical standpoint.)

Some of those speed issues you mentioned make me wonder if you have some carburetor jets plugged, although your scenario is not quite the same as mine. Especially the constant changing of max speed and power.

I had lost about 10 mph off of max speed; I took it to a shop and the guy found a wet and oily air filter from blow-back. Replaced that. He also found a few vacuum hose leaks. Fixed that and put it together for a test ride. After that, it was worse! Very slow acceleration, and top speed only about 44 mph. Next, he pulled the carb completely and found plugged jets. (I believe he may have used an ultrasonic cleaner? Don't remember.) After cleaning the carb, I had my original top speed as I recorded when the bike was new (73 mph gps.) Acceleration was way better too.

One last word on fuel conditioners: For about 5 years I was living overseas, and my People 250 was kept in storage here. I rode it for a week or two, twice a year when I came back for visits. I had used Sea Foam for a time, but tried a product called "Sentry" after a while. Definitely had an easier time starting it the first time out of storage with Sentry than I did with Sea Foam.

[ifican]

Appreciate the insight, the top end returned and part of the noise went away with 2 full tanks of heavily juiced seaform. I didnt measure but would speculate was between 5-6oz each tank. First tank it idles rough most of the tank, second tank was much better. Somewhere towards the end of the first tank i realized it was helping. So needless to say i am sure it was gunked carbs, but where we differ is i put about 150 miles a week on it and it has never sat more then 3 weeks and thats not that often.

As for the other part of the noise i discovered the rubber grommets on the heat shield thats screwed to the muffles has rubbed to nothing, so the tambourine sounds for me are from that. It only seems to do it at certain speeds and or wind conditions, that one took a little while to figure out.

My only real issue is i am a bit lazy when it comes to dealing with this stuff, my free time is much more valuable to me so i would rather drop it off to someone and let them deal with it. Problem around that is we dont have many shops around that work on scooters and the one thats the best known i will never deal with again. So i have made my own bed in that regard. As to air filter it was a bit dirty but otherwise doing what an air filter is suppose to do, no other evidence for me of any issues there. When the carb was taken apart was anything changed / dealt with (float) or just cleaned. I was really hoping it would fix itself with cleaner as i really didnt want to tear apart but appears i will need to after all.

[zombie]

This is making me think of what we call "stacking". It's when you have enough "micro" debris in the float bowl or fuel filter to get sucked into a stack, and block off fuel flow until the engine is shut down, and that stacked up debris settles out. It can happen over, and over, and over.

Sometimes conditioners will help by dissolving some organic particles but mainly the solution is disassembly, and thorough cleaning right down to the fuel lines. In fact for the cost of a couple feet of fuel line is may be best to clean/replace everything from tank to carb.
Inside the fuel tank, and on top of the petcock is a stainless steel micro mesh screen that also should be removed, and washed out w/ Carb Cleaner. The gasket on the petcock/tank is pretty stout so no worries about needing a replacement for that. Those screens are so fine that even sludge from water ( it's in ALL fuel) can block the flow. for an '07 model i'd say it's due for a "makeover".

Maybe some of this will help, and for sure it couldn't hurt

[ifican]

All great points and completely what it feels like, though last ride it got stuck at one point at only 50mph now that its been sitting a couple days i bet i would go hwy again no problem. And you can be damn sure i will replace the lines i can easily get to because i hate having to go back a second time for something that should have been done the first.

[zombie]

Keep us posted.
I just posted on a thread with similar symptoms, and it is still on going. The fella w/ the toasty valve.
Lots of similarities between the two posts... I wonder if they have a common denominator??

[ifican]

Dont feel like searching so am going to take the lazy route and post here. The symptoms initially made me suspect tight valves. So i took it to local guy and had him adjust. Exhaust was spot on but intake were rather tight. Didnt fix the problem but definitely was contributing as the bike would work less and less well as it got hot, cant hurt might help. I was about 7k on last adjustment. I dont remember what kymco calls for but i think it is 4k check if i remember right. So if he has not done them in a while or does not know last time its worth checking.

[ifican]

Ok time for more input. Pulled the carb and one of the jets was a little gummed but all good now. Spark checkedt out good, compression may be suspect but i need to find more numbers. it would start out about 90 and go to 120 after 5 or 6 cranks. The interesting piece is while fooling with it seemed to have a small air leak around the intake boot side of the carb. As a test wrapped a little electrical tap around carb side remounted and it still seems to have a little leak. Cant tell if its the throttle arm or intake boot. Boot looks crack free but who knows. Local mechanic i was chatting with says change the carb.  Remember when this first started bike would only do about 35, though maybe emissions screwing with stuff. so plugged off emissions and seems to go back too starts really slow till 30 or so then takes off again. But it has been exhibiting that behavior previously so not sure if its random or emissions. Either way still not fixed. Input on any of the above?

[zombie]

Compression will build on each stroke. BUT if there is a valve leak it will build slower. Usually 3 cranks gets it up to top psi.
A gummed up jet means lean, and lean burns valves. What color is your sparkplug tip? Look inside the ceramic part too It should be like a coffee color. Any white/tan/fuzzy appearance is not good.

Those rubber boots fail ALL the time. What makes you think it is was leaking? Usually they crack, and it is easy to find if you flex them around.