Got and Air Leak somewhere running LEAN By Saber (Read 1,429 times)

[Saber]

Okay i'm the second owner of a jonway 54b honda clone 250cc. I have done most of the maintenance to the bike because I knew the previous owner. Here's the long story. Started to die on acceleration about a month ago it started as a stumble and over a month it turned into a stumble and die. Found the plug to be white and not to good looking. Further digging brought me to a cracked air box a broken air filter mount and a crack in the snorkel going from the air box to the carb.
So I decided this is the time to dump the air box and go with a Uni filter.
I had great success on my Znen 150 and loved the results.
Anyway. I replaced all vacuum lines and tees. removed all emissions equipment. All new fuel lines and filter. Oiled and installed Uni filter. Changed the main from a 102 stock OEM jet to a 120. and replaced stock NGK with a iridium.

Bike stumbles and burps from 3000 to 5000 rpm and smooth cruises at 5500.
After a 20 mile ride the plug looks white with a splash of tan.
Also the air mix needle dialed all the way in and the bike runs? I found this out while trying to get a RPM change while trying to adjust air/fuel mix.

I need some thoughts and ideas please.

oh and almost forgot yes my valves are good

[ellpee]

Can't offer a solution, but want to throw in that on my Roketa 250 I too discovered a broken bracket inside the air box. Looks like maybe a "weak link" in their QC.

[Barnie]

Sabre, my first guess on this one would be you have a dirty carb. That is why your air/fuel mixtures screw doesn't work. If it were mine I would pull the carb and clean it good. Make sure the pilot jet is good and clean along with the small holes on engine side of throttle plate and the balance of carb and jets to. The pilot jet controls your mid range rpms/speed and the main jet covers your upper end of the rpm/speed range. Set your air/fuel screw at about 2 to 2 1/2 turns out after you put it back in. Also make sure you have no air restrictions in the air box etc. Barnie

[Barnie]

Sabre, with a jet that big you are giving it "plenty" of gas and same with the uni filter, plenty of air and most cases rejetting and removal of stock air box and filter will cause further upgrades to the exhaust system so the engine can get rid of the fuel/air. You did not say which engine u have, the 244 Honda or 257 linhai. I have found that when you start to deviate from factory settings etc that new problems arise. Try cleaning the carb, if it is the linhai 257 put a 115 main in and repair and re-install the factory air box with factory filter. Lets see what some other guys have for an opinion on your problems. Barnie

[Saber]

It's the honda clone 244cc. I probably should of posted that before doing all the changes I cleaned the carb. Because of the nature of how broke everything was before removing the air box and such there is no repair its only replace and the cost does not justify replacing.
I also should of posted I did a plug check and it leads me to believe that I am still lean on the main jet but I need to get the air leak / running lean on low and mid range before switching that out. Going to pull the skin off tonight to get access again a buddy reminded me that the intake on these bikes use O-rings it could be as simple as that.

[JR]

3 things if you are lean then you either got a air leak and/or too small of a jet. Raising the needle will help too.

Also have you checked the valve adjustment? With you trying to tune it now with a unifilter the valve tolerance is more critical.

JR

[Saber]

hey JR. I verified the valves about a week ago following your guide. Also I pulled the fluid needle out, and on this bike it's not adjustable but I was able to put a small washer under it. It did reduce the the burping sound on acceleration but I still have a loss of power on the mid range.

[ellpee]

Sept 22, 2013 19:11:02 GMT -6 Barnie said:

... You did not say which engine u have, the 244 Honda or 257 linhai. ...

Au contraire -- first sentence of first post says Honda!

Lots of good stuff here about carbs for newbies like me, thanks to all.

[Saber]

Sense my pilot jet isn't stamped does anyone know what the stock pilot jet size is?

[alleyoop]

I have to say your main jet is TO BIG, going from a 102 to a 120 is a dramatic change.

That is most likely why it stumbles in the mid range running to rich in the mid-range. If you put on a free flow filter you should only go up 2 sizes on the main jet. As far as the PILOT JET Should be no more than a #38, maybe the last owner put in a #40 or it was a #35 and he put in a #38. But see if the jet is marked and go down to the next size on the pilot jet. When you start to close the FUEL RATIO SCREW it should start to kill your motor about 1 turn before it completely closes.
Alleyoop

[Saber]

So stock would be a #35??? I new the previous owner and the pilot jet was never changed. My plug is white that's lean right?

[Saber]

well I figured one thing out. my air/fuel mix screw is for fuel and not air. because it is on the engine side so screwing it in makes it more lean. Thats why the bike runs better with it about 3 1/2 to 4 turns out. Stock it was 2 1/4 turns out. So now I know I need a larger pilot jet. Sorry if I created some confusion out there. Funny how different a 250 is from a gy6 150.

[alleyoop]

If you cannot kill the motor turning it CLOCKWISE LEANING it out that means the PILOT JET is TO BIG OR the POINT on the Fuel Ratio Screw is NOT POINTED anymore someone turned it HARD when closing it and flattened the point off and is now NOT shutting enough of the fuel off in the passage when you screw it all the way in.
Alleyoop

[Barnie]

Saber, not sure what size jets your Honda 244 uses but my linhai257 came out of factory with a 38 pilot jet and a 115 main. It is 6 years old now and still all stock. Your air/fuel screw is mainly for idle/low speed, pilot is for mid range and main is for high speed. From what you have said that all other areas of engine are ok I still suspect dirt in your pilot citcuit expecially in the small holes on engine side of throttle plate. The factory builds the engines where valve clearance,jet sizes,air volumn work in unisome for best performance. If you change 1 the balance will be off and performance suffers. Normal setting for air/fuel setting will be about 2 to 2 1/2 turns open. Yours is not working as I suspect your jet and uni filter have the balance way off in the carb. The more fuel and air you pour into an engine the longer the valves have to stay open to handle it and the more exhaust it creates mean you need to increase the exhaust system in size so the back pressure is not to great. Keep trying, hopefully you will find the gremlin. Feel free to ask anyone anything.

[ellpee]

Wow, all this really motivates this newbie to NEVER screw around with the carb unless the situation is dire! But it's all very educational, my thanks to everybody who's contributing to the discussion.