Carburetor kymco 250 people s and high speed problem, black spark

[escor]

Hello

I am almost 50, do live in Switzerland and I just purchased a kymco people s250 in blue with about 6'000 miles. I am very happy with this scooter.

I changed the spark, the engine oil, the transmission oil. But I am a office clerk "without" mechanical know-how.

The air filter was totaly dirty with black dust: but I had not a new air filter, so I cleaned the air filter with pressured-air. It is now "cleaned" and quite OK.

My problem: the kymco runs still only up to 90 km/h quit normal, but then it takes a long time to get up to 110 km/h. And 110 km/h is the high speed... but it should be 130 km/h on the speedometer. (I have an older foresight 250: an the foresight runs much more faster after 100 km/h).

After my cleaning und maintenance and changing oil, the kymco was only a little bit faster, but still too slow after 90 km/h.

(sorry for my english, I try my best....)

The old spark (which I replaced) was black on the top. So I think, that there is too much fuel?

So I have two questions: 

What can be the reason for the insufficient top speed?

Can it be the carburetor? How do I adjust more air oder less fuel? I know the idle screw, but where ist the screw to adjust the air-fuel mixture? In which direction I do have to turn the screw?? Does any one have a picture of this screw?

Is there another possible reason for the low top speed?

Maybe I have to adjust the valves? 

Or can it be the choke (not dismissing 100%?) ?

I am glad about every tipp and hint! And I hope, that I will found some help in this huge forum. Thanks a lot! 

Wish you a warm spring time an hot summer

Yours, from Switzerland

Edi

[escor]

 

[TLRam1]

What a beautiful bike! I would doubt it is the valves but never rule out anything, probably more like the carbs. With no history on the bike it is hard to say, it could be a lot of things overall.

1. Did the bike sit for a period of time?

2. Have the rollers been changed?

3. Was the previous owner a tinkerer type person?

4. Does it feel like it runs out of power, misses, backfires, etc?

Many more questions can be asked but we are shooting in the dark.

With you having no mechanical skills maybe you should find a shop and take it their.

[hypophthalmus]

I agree that it should be able to hit 130 km/h.

If I recall correctly, the screw on the carburetor only adjusts the air/fuel ratio at idle and low speeds. It could be that the carburetor needs to be thoroughly cleaned though.

Definitely replace the air filter. That's a reasonable explanation for a rich mixture.

Valve clearances are something you should check regularly anyways, so if you don't know when they've been checked last I'd recommend doing it.  You're also probably due for a new fuel filter.

[hypophthalmus]

Also, not relevant to your problem, but it's also a good idea to replace the brake fluid if it looks dark. It'll absorb moisture from the atmosphere just by sitting.

[escor]

Hello

Thank you very much.

1. Did the bike sit for a period of time? It was used very few the last 2 or 3 years. But it was used for small trips on sunday.

2. Have the rollers been changed? No, there is nothing changed (not the rollers where the belt is transmissioned).

3. Was the previous owner a tinkerer type person? No, but very old. The maintenance was made by a kymco dealer at 300km, 3000km, 7000km and 9'000 km (2 years ago). The kymco was used rarely the last two years (the owner got retired).

4. Does it feel like it runs out of power, misses, backfires, etc? Not at all: the scooter goes very good and smooth but strong. The acceleration is great up to 80, 90 and then it's over. I was today on the high way...with wind in the back I did about 105, maybe 110. Against the wind 100.

But changing the fuel filter is a good idea. And of course: I will also change the break liquid: I changed it two times on my honda, so I know how to do. Maybe this change will make the scooter faster   

Cleaning the carburator? This is something I have to let do the dealer.  But here in Switzerland, the Dealer takes 100 Dollars / hour and I do earn 22 dollars/hour... And If the dealer spends two or three hours, this makes me "poor" 

I bought today the new air filter (about 39 dollars...): I will replace the cleaned, old filter tomorow. Maybe there will be an effect.

But it is not very nice to feel no acceleration. I can not overtake a truck safely. With the old 250 foresight (which has 35'000) I can easy overtake a truck that drives 110 or 120.

Thank you very much. I will report you, if I find out something.

Yours

Edi

[hypophthalmus]

Here's a cheaper option for air filters in the future: http://www.ebay.com/itm/HiFlo-Air-Filters-HFA5006-551-5006-/262497090216?hash=item3d1e0bbaa8:g:8AoAAOSwHoFXsDy1&vxp=mtr

Or just do a search for HFA5006.

[escor]

Hello

I did change today the air filter. I cleaned also the fuel filter with pressured air (seemed to be ok). And I cleaned the variomatic/transmission (there was just dust, but it was quite clean). It was much easier to open the transmission-cover than I thougt.

Then I went on the high way...puh...100, maybe 105 km/h.

I went to an hill and then I got on 120 km/h downhill, not more. But later, on the high way, I had 110 to 115...

So I think, the high speed will come better an better: the scooter just need some highways drives??

But still: compared to my honda 250 or to an Yamaha x-max 250, the people is very slow, no power. Up to 80 it is realy ok, but from 80 on up to 90 the scooter is weak. And from 100 to 110 I can count slowly to 50...

Maybe someone has another idea?

I will try to make some "high-speed"-drives and I hope, that the scooter will get used to it... it seems like if I had to force the scooter to drive faster again.

Thank you


Edi

[Redk]

Must be a fun place to ride a scooter !

What is your elevation ASL ?

Naturally aspirated engines lose 5% power each 1,000 feet above sea level.

My guess would be your elevation is the reason for about half what you view as a problem.

It's merely a result of circumstances.

The tiny 50cc engines can't hardly get out of their own way at the higher elevations.

Have fun !
redk

[Mr. Paul]

A black spark plug usually means there is too much fuel for the available air. Yep, altitude could be a cause of this. Changing your filter was a good thing to do. It would not hurt to lean out your air/fuel mixture screw some in my opinion. I too am waiting to hear what your altitude is. By the way, that is a beautiful scooter!

[hypophthalmus]

Concerning altitude, I think you're missing the part where the bike is performing unfavorably compared to other 250cc scooters.

If driving the problem away is helping, you could try accelerating matters with some kind of magic fuel additive (seafoam, b12 chemtool, and techron for instance are available in the US anyways).

If you are going to change the idle air/fuel mixture, there's a picture in the manual at 3-6.

You'll need a tachometer and a long flathead screwdriver. I think I recall it fitting through a hole in the frame to the pilot screw.

If I recall correctly, tighter is richer, looser is leaner. First you'll want to find the point where the rpm is the highest. Then find the two points where the rpm drops by having it too lean or rich. Set it in the middle on those points, then turn it 1/8 turn richer.

[Redk]

From where I sit, lacking all the information, in an ancient thread,  ...lol

Adjusting that idle mix isn't going to make much difference.
It will be necessary to pull the carb, at least enough to roll it over and remove the main jet from inside the float bowl.
You will need to work with it, so write down the number stamped on it representing the jet size.

You might begin selecting the replacement main jet by purchasing one that is 4 or 5 digits higher than the existing one. This will lean out the air/fuel mix at higher operating speeds, and down through mid-range. Re-assemble and go for a speed run.
If it spits back out of the intake at high speed, the main jet is now too small.  Allow the engine to cool as you motor back to your shop and do not run the engine while it is set up lean.  This can be bad for the engine.

Of course it would have been better to purchase 2 or 3 additional jets, when you were at the parts dealer, but it gets kinda pricey, and it's most likely you will never use them again, unless you make a serious change to the exhaust system, or install expensive performance parts within the engine.
Chances are, the dealership may not have jets in the size you require.

There is another option.
First, you must have the tools on hand to do the work.
A decent soldering iron, flux, and solder, and a number drill set with pin vice, in the range necessary...  and this goes back to, you must disassemble to find out what is in there, before anything may be done.

If running rich at WOT, you may determine by trial and error, which of your small drill bits is a proper fit for the main jet.
Assure yourself you have the consecutive drills smaller than that size.

Solder the main jet closed, then drill though the solder in a smaller size.  Perhaps 4 sizes smaller.
If it shows a lean running condition at WOT, pass the next drill size up, through that solder and run again.
You must retune the idle mix each time you do this, but it will be a quick process, since you should already be reasonably close.

Some main jet needles have a selection of circular grooves near the top where a circlip adjusts the height of the needle, controlling flow from the main jet for mid to high range ratio. A groove closer to the top of the needle will make it leaner, lower down will make it richer.
Better to be a very little bit rich than lean, which builds heat to quickly.

There are also needles with different tapers and they interact with the main jet like a finger in the dike, As the needle within the slide is withdraw upwards, a change in the taper will influence fuel flow.

There are a number of other things to fiddle with, if you are heading towards the winning circle, yet that is beyond the scope here.
it is most likely you will not need to replace your needle or the emulsion tube.

redk

[escor]

Hello 

Thanks a lot to all and specially to REDK

I do live on about 800 Meters. So there is no problem with high altitude. But when I go up to the mountains, the foresight 250 runs about 60 km/h on 3000 Meters... big difference.

No: the 800 meters are "nothing" to consider.

I will try to run some highway Kilometers and then I try to adjust the carburetor as REDK told me: I hope, I will achieve this.

Thanks

Edi

[RatBob]

I have an '07 S 250, tuned to perfection it's top speed via GPS is 76 on flat ground, calm day. 0-60 will keep most cars off your tail and it will keep up with any 250cc bike I've encountered until that magic 60 at which point they drop a gear a disappear while I creep up to 76.

[TLRam1]

Process of elimination, give the carburetor a good cleaning, all jets and passages. make sure the gas tank supplies enough gas.