performance problems w/ my Jonway YY250T CFMoto Engine By rsw1158 (Read 4,497 times)

[rsw1158]

Thanks, I'll do.

[Saber]

May 1, 2014 14:11:47 GMT -6 rsw1158 said:

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.   

How is all this working for you right now? What jets are you using. I am having similar issues with my bike but my issues is in the 3500 to 4000 range.

[rsw1158]

Well, funny you should ask. I'm having issues again. It was running good for a few days, and now it is back to surging again in the mid range. Again, it is loosing power under load ( heavy head winds ) and bogging down. If I back off the throttle, it will smooth back out. Acting like it is too lean. Eventually I will get to the bottom of this problem.

[Saber]

May 13, 2014 10:12:33 GMT -6 rsw1158 said:

Well, funny you should ask. I'm having issues again. It was running good for a few days, and now it is back to surging again in the mid range. Again, it is loosing power under load ( heavy head winds ) and bogging down. If I back off the throttle, it will smooth back out. Acting like it is too lean. Eventually I will get to the bottom of this problem.

Well Damn,
Same issue under load going up a hill or if I try to rabbit start off the line but it has to be hot outside (above 80°) if I'm at WOT though she runs like a top.

[rsw1158]

Have you done any mods to your scoot? How many miles on it? What engine and what year is it?

[rsw1158]

I went out and bought a new carb today. It looks a lot like my oem carb except it sais Japan on the side. I opened it up and checked the jets. It had a 108 main and a 37 pilot. I changed them to a 125 main and a 38 pilot. I also checked the needle valve. Mine on the oem carb was not adjustable. This new one is. It has 4 slots for the clip. It was set on the lowest slot. I changed it to the second to the top slot. I installed the carb and started it up. First thing I noticed is that the enricher worked like it is supposed to. Before, even after trying a new enricher, it would start up slow idle and idle faster as it warmed up. That would be wrong. Next, after it warmed up, I tried to adjust the mix screw. It also acted like it was supposed to. Before, my carb was unresponsive unless I screwed it out a bunch. I made all my adjustments and took it for a ride. It is stupid windy today. Earlier today when I was working on it with the old carb, I could only go 60mph and it was bucking and surging and would smooth out after I backed off the throttle. Now, it goes 70mph against the wind and no bucking or surging. The old carb was the problem. If anyone that has this same scooter and having these problems, get rid of that junk carb. Find a quality carb and enjoy the ride. I hope this post will save a lot of headaches for someone else.    

[JR]

Awesome! Glad ya got it worked out. New carbs are cheap and easy to install, bought a new carb for a little errand 50cc scooter today, $22 delivered.

JR

[Saber]

May 13, 2014 17:10:50 GMT -6 rsw1158 said:

I went out and bought a new carb today. It looks a lot like my oem carb except it sais Japan on the side. I opened it up and checked the jets. It had a 108 main and a 37 pilot. I changed them to a 125 main and a 38 pilot. I also checked the needle valve. Mine on the oem carb was not adjustable. This new one is. It has 4 slots for the clip. It was set on the lowest slot. I changed it to the second to the top slot. I installed the carb and started it up. First thing I noticed is that the enricher worked like it is supposed to. Before, even after trying a new enricher, it would start up slow idle and idle faster as it warmed up. That would be wrong. Next, after it warmed up, I tried to adjust the mix screw. It also acted like it was supposed to. Before, my carb was unresponsive unless I screwed it out a bunch. I made all my adjustments and took it for a ride. It is stupid windy today. Earlier today when I was working on it with the old carb, I could only go 60mph and it was bucking and surging and would smooth out after I backed off the throttle. Now, it goes 70mph against the wind and no bucking or surging. The old carb was the problem. If anyone that has this same scooter and having these problems, get rid of that junk carb. Find a quality carb and enjoy the ride. I hope this post will save a lot of headaches for someone else.    

Where did you pick up the new Carb? As we all know not all internet parts are the same or of any sort of quality.

[rsw1158]

I stopped at a Roketa dealer on my way to the lake yesterday. I just dropped in at chance to see what he had. He pulled this carb out of the loft and I inspected it noticing it had Japan casted on the side of the carb. I heard those are the good carbs so I went for it. He said his cost on that carb was 125.00. He sold it to me for 157.00. I was desperate so I bought it. It turned out to be the right choice.

[Saber]

May 14, 2014 6:16:14 GMT -6 rsw1158 said:

I stopped at a Roketa dealer on my way to the lake yesterday. I just dropped in at chance to see what he had. He pulled this carb out of the loft and I inspected it noticing it had Japan casted on the side of the carb. I heard those are the good carbs so I went for it. He said his cost on that carb was 125.00. He sold it to me for 157.00. I was desperate so I bought it. It turned out to be the right choice.

Do you have any mods are yours?
I had to drop the air box because everything related to it broke so I'm running a 2 stage Uni filter.

[rsw1158]

There are a few mods I have done to my scoot. The first thing and the biggest thing is to get rid of the emission stuff. I disconnected the charcoal canister and got rid of the air box. There are some hoses you have to deal with when you do that. The crankcase vent hose has to have a pcv valve installed and then after the pcv valve, I installed a fuel filter to keep contaminates out. You also have to run the hose so the end of the hose is higher than the head of the engine to keep oil blow-by at a minimum. I ran mine up and at the back of the frame under the rear seat. Just make sure that all the vacuum hoses are hooked up that needs to be hooked up. You need manifold vacuum to your fuel pump and the valve on your carb. I installed a higher volume makuni fuel pump, better quality and better reliability. I have an egr valve on the exhaust pipe that is disconnected and the hose is just zip tied up out of the way and not blocked off. I disconnected the fuel tank vent because it got clogged up from filling my tank too high all the time. The fuel will run back into the vent hose and saturate the charcoal in the vent and cause it to plug up and then your scoot won't suck gas up because it causes a vacuum lock. I vented the gas cap by drilling an 1/8 hole in the top of the cap. Problem solved. I run a Uni style foam filter off of the end of the air box snorkel instead of right off the front of the carb. It seamed like it was getting too much air. When the filter was on the front of the carb, the exhaust sounded blatty, like it was too lean. With the filter on the end of the snorkel, the sound is deeper and seems to run the best that way. I opened up my oem muffler because I had a rattle in it. I discovered that there is a catalic converter in it and it had fallen off. So, I moded my muffler. I cut the cap off the exhaust end of the muffler and cut out the tail pipe. I enlarged the hole in the rear baffle to except a larger ID stainless tail pipe. The oem tail pipe is installed so it goes through the rear baffle and only MM from touching the next baffle. When I installed the new tail pipe, I made sure it just barley penetrated the rear baffle and welded it there. That would free up some restriction and deepen the sound of the muffle. Also, when I had the other end of the muffler open, I cut a section of the exhaust pipe out so the exhaust would not travel through the pipe route inside the muffler but instead, travel through the baffle hole straight out the back of the muffle. That frees up more restriction and makes the muffler a little louder. Not too loud. So now, the engine is a more efficient air pump. More air in, more air out. Now, at this point it will respond to rejetting like it should. I took out my oem roller weights in my variator and installed 20g slider weights. That causes my scooter to operate at a higher rpm letting it operate closer to it's optimum power output range. And there you have it.           

[alleyoop]

Good that it is running good now, but I have to say if it started to act up and then you backed off the throttle and it settled down then it was to RICH to much fuel. IF when you backed off the throttle a little the sped up it was to LEAN.
There are tricks of the trade I put up here in the TIPS AND TRICKS section and or AIR AND FUEL SECTION that tells you what the MOTOR needs either by the sound it makes or like the trick of the trade I just mentioned. The carbs on these scoots are really pretty simple and only a couple of things gets them out of sync with the amount of air and fuel.

It could save you lots of time and money if you guys would check out the info on here.
Alleyoop

[wheezy]

May 16, 2014 12:38:58 GMT -6 alleyoop said:

Good that it is running good now, but I have to say if it started to act up and then you backed off the throttle and it settled down then it was to RICH to much fuel. IF when you backed off the throttle a little the sped up it was to LEAN.
There are tricks of the trade I put up here in the TIPS AND TRICKS section and or AIR AND FUEL SECTION that tells you what the MOTOR needs either by the sound it makes or like the trick of the trade I just mentioned. The carbs on these scoots are really pretty simple and only a couple of things gets them out of sync with the amount of air and fuel.

It could save you lots of time and money if you guys would check out the info on here.
Alleyoop

The problem though is that the symptoms are sometimes not that black and white. Take my bike, for example. It never would make the classic rich or lean sounds, no popping, no backfiring. What i noticed, only over time, was a pattern in how it would act. It runs better in the morning than the afternoon. In the morning I could go full throttle, the afternoon it would cut out after 3/4 throttle. I ride 45 miles home, and it would cut out almost in the exact same locations every day. The only commonality was temperature, humidity, and load. In the morning, the cooler, less dense air would mask the richness. The warm, more dense (especially with humidity in Florida) air would bring out the rich symptoms. The hills I ride through would really load the bike, and it would stall. 30 seconds of cranking would get me to the next hill. But then once I passed through the hills, the last 15 miles would be stall free. The symptoms never added up to rich OR lean. Until.....

I kept asking myself why a bike with the same jets and mixture as last year would suddenly not run right this year. Nothing had changed, other than the age of the rubber materials in the carb. Why should I be changing jets when it ran fine before? Seems I would be masking some other problem. The valves, vacuum, and all the other suspects were ruled out over time.

After playing with the float for almost two straight weeks, here's what I noticed. The float shutoff valve would either be fully closed allowing in no gas at all, or the carb would flood from too much fuel. There was no happy medium. I adjusted the float tang all through its range, and it still would either not open or flood. I only noticed the flooding once I installed a clear bowl drain hose, so I could monitor the fuel level real-time.

So, in my opinion based on weeks of toying with this, is that the rubber stop on the float valve gets worn (it still LOOKS the same to me). It's just not doing the job anymore of controlling the flow. After all, my scoot is 7 years old, and who knows how much older the carb is.

I also have a new carb on the way. Hopefully, this does it. But, like rsw1158, a new carb (or even a rebuild kit) may be the solution to a whole lot of these Jonways having the same stalling issue.

[alleyoop]

All that you said is just AIR TO FUEL mixture problem that is all and from what you said it is due to temp changes and air density at the time. You can adjust a carb to handle pretty much both extremes of temp and air density but they will always run better when it is cooler than when hot. Now a car has a computer to adjust for this but our carbs are fixed so you have to adjust them to run pretty good in both sides of the temps and air density.
Alleyoop

[wheezy]

Alley, i cant speak for OP, but in my case I don't think changing the mix or jets would have solved anything. According to the fuel level indicated by my drain hose, my jets are likely submerged, so much that the atomizer holes could not function. Literally, the level was equal to the bottom of the venturi itself. I got a pic, but it is low quality so not worth posting.

I looked into the fuel injection upgrade everyone talks about. It has the ecm and o2 sensor that would compensate like you were talking about. Just can't justify 400 bucks right now.