Popping through the carb By rsw1158 (Read 1,184 times)

[rsw1158]

I thought I had this running good but now this popping is getting worse. I have a 2013 Jonway YY250TT scooter with the CF250 engine. The scooter is popping through the carb when it is running at 4000 rpms to 5000 rpms. It also won't hold steady at thoughs rpms and will actually surge with bigger than a 138 main jet is installed. I have been trying different jet combinations to see if I can clear it up but it will only get worse but not go away with the different jets. I don't find any air leaks at the intake or carb area but I do have a small leak at the exhaust flange I can't stop. I even tried a different cab but it still does it. I also noticed that I have very little response at my air fuel mix screw. I can turn it all the way in and it will still idle great no matter what size jet I put into it. It has always done this with the air mix screw ever since I found a tool that could get to it and that was about a 1000 miles ago or so. I've have 112 to 144 mains in it to test different combinations. Do I have a valve problems or what is going on? I have 3300 miles on it. All highway miles.

Read more: itistheride.boards.net/thread/5754/popping-carb#ixzz2zqaMKZDv

[Alleyoop]

It is running LEAN. You need to seal the Leak at the FLANGE, You need a new gasket or the weld is broken there. A leak there sucks in a lot of air and will run LEAN which will cause popping and surging.
Those 30mm carbs usually come with a 138 main jet, and do not change the PILOT JET.
Alleyoop

[rsw1158]

I took the muffler and pipe off and could not see that the gasket was even bad or burned. So I messed with the clamp to make it round again and put it back together. I thought I fixed it. I could not feel any air putting out around the flange. But then again tonight after looking at it, I could see the white/grey residue around the pipe again. It looks like I need to order the short pipe/flange and the gaskets. I think the pipe is not round causing it not to seal properly. This engine came with a 32mm carb and when I checked the main jet last year when I bought it new, I believe the main jet was 112. I thought then that was rather small. I have been experimenting with different jets since. Now, I don't remember what pilot it came with. I have a 36, 38, 40, 42. I have the 38 in it now.

[Alleyoop]

Well you won't get it adjusted right until you stop the air leaks. Otherwise it will run differently at different throttle positions. Air Leaks around the carb area or intake will cause low end bogging and or bog when given any throttle. Exhaust leaks will be noticed at high rpms and or deceleration.
Alleyoop

[rsw1158]

Thanks again and I'll get these issues taken care of. I think I had this exhaust problem from day one.

[Alleyoop]

The exhuast where it connects to the motor is very flimsy. The pipe is very thin and the wider part on the end is welded to the pipe. You may want to take it to a welder and actually have him build you a new piece with a thicker piece of pipe to slide the flange onto.
Alleyoop

[Bashan]

I responded to you on the other forum, you can read my thoughts. Alley is 100% correct. Rich

[rsw1158]

Yep. I am not disputing this at all. It is very obvious that the metal is very flimsy and inferior as is all the metal works on these Chinese scooters. A guy has to wonder about there process for making there threads. I think there is some poor old soul sitting in a sweat shop with a file and a stool and just filing away at metal parts to make something that resembles a threaded bolt or stud. It seams like you take a nut off something more than once and there you are, trying to figure out how to repair that stripped out stud or bolt, and or threaded hole. Very aggravating. And also, you are right Alley about my carb being a 30mm carb. My mistake about being a 32mm. I was wondering. Are Honda parts made any better for the CF250?

[Alleyoop]

Yes Honda parts are quality parts but you pay through the nose for them
On my Trike I had a HotRod shop make me a complete header pipe with thicker pipe and 1/4 wider piping.
Alleyoop

[rsw1158]

Well. Here I am again. I replaced everything. New pipe and gasket. New exhaust pipe seal and clamp. Made sure everything was round and sealed correctly. And, I also replaced my intake manifold to be sure I had no air leaks. I had a new surprise when I took off my intake. I noticed a notch in the casting of the head where the o ring of the intake manifold would have to seal. Is that a flaw or is that there on all of these? It looked suspicious so I smeared RTV black on it to make sure it seals. After all that, nothing changed. I still get no response at the mix screw and I get the popping through the carb between 4K and 5K and a little surging in that range. I have a 138 main jet in now with a 38 slow jet incase you where wondering. Also now my temp gauge must have gotten tiered. It stopped working. It never ends.

[Alleyoop]

OK, when does it MAKE THE POPPING SOUND:
1. As it is excelerating?
a. To much fuel or Main Jet to Big.

2. At Idle?
a. To much fuel or Pilot Jet to Big or set to rich or extra fuel is being sucked in from someplace.

3. When you de-celerate?
a. To Lean, needs a little more fuel or idle set to low.

Alleyoop

[rsw1158]

I took it for a 10 mile test ride. It is very windy today so it was a good test. I did not have any issues while it was under driving load. All seems good. No popping on decel or excel or at cruise. No loss of power. Only does it when it in the garage while trying to tune it. It bothers me that I have no response at the mix screw.

[Alleyoop]

When tuning in the garage let it warm up at least 5 minutes so the Enricher cuts off the extra fuel.

Now it should be idling at around 1800-2000 after it is nice and warm and no surging nice and steady idle they do fluctuate but only 50-100 rpms but you cannot even notice that unless you have watch the tach.

But after it is warm and you turn the Fuel Ratio mixture in either direction 1-2 turns wait about 10 seconds after each adjustment to let the motor catch up with the new setting you should hear the IDLE either go up or down or see the tach rpms drop or rise a little. IF it does nothing then turning the Fuel Ratio screw is NOT changing the amount of fuel being allowed to flow through the Pilot Jet passage. It could be the Point on the Fuel ratio screw has been broken off and its a constant flow of fuel no matter what you do.

So I would take the screw completely out and also check that the needle point is still in tack as well that the tiny washer and o-ring are present and in good condition.
This is what should be in there and in that order:
Alleyoop

[rsw1158]

Very good. I will check that in the morning. I don't know why I didn't think to check that before now. It would make me feel a lot better if I find the problem there. That is an easy fix. Thanks.

[rsw1158]

I just checked the mix screw. I thought I had found something but ended up being nothing. The washer was not there. The spring was setting up against the o ring and the washer is non existent. After taking parts from another carb to make it right, the only thing different is that it idles smoother. Still, I get no response from the mix screw in either direction. There is something else that bothers me about this scooter. Since new, In my mind the auto enricher never worked right. When I start it up cold, it idle slower, around 1k. As it warms up, it will idle faster until it reaches about 1800rpms when fully warmed up. I called the company I bought it from and they sent me another enricher. It acted exactly the same way. Hmmmmm? maybe that is the way it is supposed to be on these. I am used to my old 150cc where it acted the opposite and I could adjust the carb mix screw. This thing is acting nothing like that. I would like to hear from others who have this same type of scooter with the 172mm 250cc engine on how it acts while warming up and how it runs out right. Maybe I am all wet in thinking something is wrong with this scooter. What are your thoughts?