performance problems w/ my Jonway YY250T CFMoto Engine By rsw1158 (Read 3,891 times)

[rsw1158]

I have a 2013 YY250T with a CFMoto Engine I am having on going problems with. I have 3300 miles on this and I have had these problems since day one. Basically, it runs good until you have heavy head winds or when it is calling for more power than usual. Then, it will start popping through the carb and lose power until I back off the throttle and let it recover. Then, it will smooth out. I noticed when I have it in the garage and trying to tune it, it will have this flat spot between 4k and 5k where it will surge and pop back through the carb. I have tried rejetting the carb but I can't get it to smooth out. It came with a 118 main jet and I have tried as large as a 138 main jet and everything in between. I have never been able to get any response out of the fuel/air mix screw. I can turn it all the way in and it will do nothing. If I back it out too far, it may start to bog down just a bit. The exhaust was leaking at the tube gasket so I replaced the tube, seal and gasket, and the clamp. I also replaced my intake housing because I had the carb off so many times I was afraid a leak may have started there. When I took the intake off I noticed a notch in the casting of the sealing surface of the head where the oring of the manifold would have to try and seal. is that a flaw or does all these have that? Any way, I took some RTV black and smeared over that spot to seal it. So, at this point if I had any air leaks, I should have fixed them. Well, after all that, nothing changed. I did disconnect all my emission stuff and removed my air box. I also modified my muffler to accommodate more air flow. All this was going on before the mods and it is still haunting me. Any help is appreciated.      

[alleyoop]

Different sounds a motor makes tells you what it needs, so listen for any sounds the motor makes.

1. Popping while accelerating is a RICH condition.
2. Popping while decelerating is a LEAN condition.
3. Burp/Brat Sounds accelerating is a LEAN condition
4. Backfires are a LEAN condition.

Possible causes for above and fixes:
1. Here the problem is it is running OVERLY rich.
a. Enricher is still feeding extra fuel
b. Fuel is being sucked in through the Petcock Vacuum hose
c. The Fuel Ratio Mixture is to rich
d. If you changed the main jet it is to big
e. If your Carb has an ACV valve it may be sucking in fuel through the ACV Vacuum hose

2. Here couple things:
a. You can rich-en up the Fuel Ratio Mixture
b. Idling to low Bring up the idle a little
c. If your Carb has an ACV valve it may not be working and NOT allowing some fuel to flow during deceleration.

3. You can rich-en up the Fuel Ratio Mixture

4. Usually caused by it Leaking where the Pipe Connects to the motor. Bad air leaks cause the backfiring many think it is because it is to RICH but it is the OPPOSITE sucking in air causing very Lean condition and this can damage your exhaust valve.


If it just BOGS on you or starts dropping rpms or bucks but makes no distinguishing sounds then the good old Trick of the Trade will tell you what the motor needs:

TRICK OF THE TRADE:
Lets find out which situation(LEAN OR RICH) is causing the problem.
Run the sucker like you do when it STARTS TO ACT UP Back off the THROTTLE about 1/4 OF AN INCH and HOLD IT THERE:
A. If the scoot Speeds up it is running LEAN.
B. If the scoot Sputters or whatever BUT settles down it is running RICH.

This way you will know what it needs(more or less juice).
Alleyoop

[rsw1158]

 Well, this is getting more interesting every day. I would like to know the start up and running characteristics of people who own these 250cc scooters with the 172mm engine. How does it act when you first start it? Idle slow then speed up after it warms up or the opposite? Any flat spots in the throttle response while cruising? Let me know. I would like to know how other scooters are behaving. After owning this thing for a year and I can't get anything to change as far as the way it runs, I am wondering if maybe I don't have a problem.      

[scot]

have you adjusted the valves most motorcycles an scooters recomend that at 1000 miles reguardless of what others say. then they don't need to about 10,000.i have 2013 it takes time to warm up then run great so far but I only have like 100,miles on it to  don't know if there is choke on that one I don't think so. an I also been told the sooner the better with that ,its early on they need adjusting more then anything ,meening  its better to adjust them before funny noises .then it is to wait until then

[alleyoop]

From what your saying I think to much fuel is being fed when cold. I can make mind act that way with my MANUAL choke . ON days when it is not that cold If I RETRACT my Enricher all the way it will start up and idle low then if I extend it a little the rpms rise. It all depends on the temp and the amount of fuel it needs. But I do question that the Fuel Ratio Mixture does nothing when turned in either direction. If we could get the Fuel Ratio Mixture to cut off some fuel it would act like its supposed to.

How many turns is the Fuel Ratio screw out from the closed position?

Try this with the Fuel Ratio Screw but do this after it is warm. Turn the screw clockwise 1/4 at a time and see if it kills the motor.
Alleyoop

[rsw1158]

Yes I have adjusted the valves long ago and several times since I have rechecked. They have never been out of adjustment from what I could tell. I adjust them so I just start to hear the clicking. You can just barely hear them. I am satisfied with that. I am just wondering if there is something strange with the carb. I have another carb that is just a size smaller than the original, but I'm not sure that would be a safe test. The enricher wiring is different because it is not for a water cooled engine. I'm not sure if it would interfere with the cooling fan coming on or how the enricher would work. I played with thought for a while and tried to mount the water cooled engine enricher on the other carb but that won't work. Different size.  

[alleyoop]

It is not your valves, it is the carb and a fuel delivery problem.
Alleyoop

[ellpee]

Not trying to give anybody the idiot treatment here, I'm the only one that qualifies for that, but on my Magnum, where the mixture screw is on the bottom and REALLY hard to get to, I fabricated a very, very stubby screwdriver and THOUGHT I was tweaking the mixture but was seeing no difference in performance. Then I took it to a little rent-a-scooter shop in Ruidoso and learned that there was in fact a plug in the mixture screw opening -- I think that was a California, don't-mess-with-the-mixture thing. Anyhow, the guy somehow removed that plug, after which the REAL mixture screw was visible and could be turned as needed. So *** I *** was initially thinking I was adjusting the mixture when in fact I was doing nothing at all, or maybe I was turning the plug but not the actual screw. Not to say that's what's up with your totally different scooter, or that you are as clueless as I was, but just wanted to mention it.

[scot]

yes if you have done that enough .but also played with the carb then follow Alleyoops lead on this,they do sell alot of the scooters with carbs that are not adjustable ,when I got mine they sold separately an approved carb adjustable it was like 59.00 upgrade an I knew It would probley be a good idea for my 2013 ,ellpee could be right about what he is saying ,I had a atv that was like that an couse wear I live in never ran right ,I like 1000 feet above sea leval,it had idle screw but no fuel mixture screw ,that was way back when people did not know what they were getting 10 years ago

[rsw1158]

Going to remove the carb again today and inspect it. Going to spray carb cleaner in all the orifices and see if anything is plugged. 

[alleyoop]

May 1, 2014 8:30:49 GMT -6 ellpee said:

Not trying to give anybody the idiot treatment here, I'm the only one that qualifies for that, but on my Magnum, where the mixture screw is on the bottom and REALLY hard to get to, I fabricated a very, very stubby screwdriver and THOUGHT I was tweaking the mixture but was seeing no difference in performance. Then I took it to a little rent-a-scooter shop in Ruidoso and learned that there was in fact a plug in the mixture screw opening -- I think that was a California, don't-mess-with-the-mixture thing. Anyhow, the guy somehow removed that plug, after which the REAL mixture screw was visible and could be turned as needed. So *** I *** was initially thinking I was adjusting the mixture when in fact I was doing nothing at all, or maybe I was turning the plug but not the actual screw. Not to say that's what's up with your totally different scooter, or that you are as clueless as I was, but just wanted to mention it.

GOOD POINT Ellpee, that could very well be that it has the plastic plug on it and faking him out
Alleyoop

[rsw1158]

That would be a valid point if I where clueless, but I have had this carb apart before when I noticed this problem last year and it has a real needle, spring, flat washer, and o ring in the port along with an orifice that accepts the needle and the needle is fully intact and undamaged. Just wanted to throw that out there so no one would suspect it is capped. I was fully aware that some of these are capped, just like some lawn mowers and cars from yester years used to be. Been there done that from being an auto mechanic for years. This is why I am scratching my head over this. Even though I have limited knowledge on these small engines, I still know some things about carbs and gas engines. I know something is not right. I even contacted the dealer about this last year because they have there own mechanic. I could not believe how clueless he was and he was there best man. I knew then I could not rely on there help. I even talked to some motor cycle mechanics and scooter mechanics from different shops and they had no answers different from what I have been trying. So, off to the garage again I go. Thanks for everyone's input. Any other suggestions are welcome. Just wondering if anyone else has this problem and if a fix has been established.   

[alleyoop]

But now you know, you closed the mixture screw all the way and it did not change a thing and the motor kept running. so what does that say is the problem:
1. The pilot jet is to big
2. The screw is to short and not blocking or doing anything to the fuel passage.
3. Fuel is being sucked out from some other place.

Now since you have taken the carb apart and checked it all out Did you maybe forget to put the Needle Guide in, that is the gold piece that should stick out about 1/8 into the Venturi so the needle does not come completely out and get stuck.
This piece:


You can get Mixture screw and the spring,washer and o-ring kit here:
.cv-performance.com/ez-just-mixture-screw/" rel="nofollow" target="_blank">.cv-performance.com/ez-just-mixture-screw/

Alleyoop

[rsw1158]

I got it all back together and didn't leave anything out of the carb. I did notice that there was rubber residue in the air mix screw but I don't see where it was blocking anything. So I started it up and let it get warm and started to adjust the carb. Again, I could close the screw all the way and wait and nothing happens. Idles perfect. I backed it out 1 3/4 turns and waited and nothing changed. I ran the rpms up and it surges a little between 4500 and 5500 rpm. So I started backing the screw out more and after about 3 turns it started to slow down. So, I turned it back in a 1/4 turn at a time until I achieved top rpm at idle and was running smooth. Ran the rpms up and no longer have the little surge between 4500 and 5500. I took it for a test drive and it runs out perfect for now. I'm going to drive it like this for a while and see how it does. Still don't seem right about the mix screw.   

[alleyoop]

I suggest you get this kit the rubber O-ring is very important as well as the tiny washer so it does not tear up the o-ring and pushs pieces into the passage.
Alleyoop

.cv-performance.com/cvp-mixture-screw-packing/" rel="nofollow" target="_blank">.cv-performance.com/cvp-mixture-screw-packing/