Carb Tuning Help By scooteraddict (Read 1,262 times)

[scooteraddict]

Ok. I have read many different threads on carb tuning. I'm currently in the stage of trying to get my carb in the perfect range. Now you might ask yourself on how am I achieving this. Well I installed a wide band O2 sensor (for testing only) and I can see were I might be burning too much fuel and too little.

I own a 250B bike and I am running with a 40 pilot jet and a 115 main. I can tell you that with a 40, I run a little on the rich side at idle and start to lean out at about 1/8 throttle. Then I go back to running a little rich up until I hit WOT. At that point I start to run on the lean side. If I go to a 118 Main jet, then I wind up running too rich. I tried to lower the needle but back at the 1/8 throttle, I run richer then before.

Now the Question for you follow scooter riders is, what can I do to get just a little more fuel at top end without having to up the jet where I run too rich? Would changing the needle jet (not the jet needle) up would help?

[Alleyoop]

Well what I would try is a #38 Pilot Jet and the #115 and raise the Needle one notch at a time and test that. With the #40 Pilot Jet how many turns is your Air/Fuel mixture screw out.

The way to tune them is to 1st work with the Pilot Jet and Needle AND NO MAIN JET. With that setup properly it should run up to about 3/4 throttle then it should start to stumble because you have no main jet. Then you can work on your main jet.
Alleyoop

[scooteraddict]

The orignal pilot jet was a 38 and with the needle all the was up with a washer, I would run leaner at about 1/8 throttle. The only way to get rid of the lean burn was to increase to a 40 pilot jet.

What I'm realy looking for is to get a little more fuel at WOT but going to a 118 gives me too much fuel causeing it to run rich.

[scootaway]

I have a 118 main in my Jonway (40 pilot) and a gas analiser put it spot on, not rich not lean and the bike goes great. Remember a little rich at top is better than a little lean. Consider a 118 again. The correct main jet is the one that allows the engine to give max power. If you have time to mess around put the 116 in, find a little hill and time yourself up (say between two markers). Then put the 118 in and race up the hill again just like before. If your time is better then the 118 is better, if slower then reduce the jet to a smaller one. Its all trail and error.

[Alleyoop]

scootaway is correct, you want to be a little rich at wot to give you a little security. Don't forget as you put miles on it the valves will start to close up on you and will lean it out.
As far as running lean and or rich at low and mid-range work with the needle and air/fuel mixture and Pilot jet. If it runs a little rich as long a it does not BOG or Stumble thats fine.
I have yet to see a PERFECTLY TUNED CARB. You can get them close but just by using the sensor is not good enough, the sensors are not that accurate they just give you a ball park reading. To get the Air/Fuel mixture Perfect you have to use high end equipment.
Alleyoop

[scooteraddict]

Looking further into this with research on the Internet, I have found that its best to run at target 14.7 to 1 ratio at a cruising speed and to run richer at WOT. With this in mind, I will be going back to my 118 main.

Now the funny thing is, I found out through a few carb tuning sights, a CV slide can effect the range from idle to 1/8 throttle. What would effect this range would be the notch cut into the slide. the greater the angle the leaner it would make it and the less the angle the richer it would be.

Thanks for the input all.

[Alleyoop]

Scooteraddict,
If you have a Carb with a SLIDE they are more touchy than a CV carb that handles the raise of the needle by vacuum. The Slide type you are actually rasing the needle with the Throttle Cable, Thats why the Slide type carbs are more touchy to tune.
Alleyoop

[zugzug]

Jun 4, 2010 19:14:52 GMT -6 scooteraddict said:

Now the funny thing is, I found out through a few carb tuning sights, a CV slide can effect the range from idle to 1/8 throttle. What would effect this range would be the notch cut into the slide. the greater the angle the leaner it would make it and the less the angle the richer it would be.

Thanks for the input all.

You can also drill the hole bigger in the slide which will change its response to the vaccum used to raise the slide/needle.

[zugzug]

Jun 4, 2010 20:59:20 GMT -6 Alleyoop said:

Scooteraddict,
If you have a Carb with a SLIDE they are more touchy than a CV carb that handles the raise of the needle by vacuum. The Slide type you are actually rasing the needle with the Throttle Cable, Thats why the Slide type carbs are more touchy to tune.
Alleyoop

They all have a slide.....

[Alleyoop]

They all have a Cylinder with the Needle but they call the Carbs that the Throttle itself raises the cylinder with the Needle SLIDE CARBS.
Alleyoop

[scooteraddict]

It is correct that I do have a CV carb with a cylinder slide. Sorry if I didn't provide this information.

Having found out about the mod about drilling out to 1/8 inch, I have already done that.

Although it's a dilemma to make sure that we don't burn up our bikes with too little gas or flood our engines wasting gas, I would like to get it in the ball park for many more happy miles. Getting the right parts for the carb's is a PITA. Especially the Chinese bikes.