cg 125 cafe racer cough...... - Wrist Twisters
 
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post #1 of 17 Old 10-01-2012, 10:01 AM Thread Starter
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cg 125 cafe racer cough......

Hi there this is my first post and im keep fingers crossed for some help, i have built a cg 125 cafe bike and as part of the look i have added a k & n style filter and as such i have had to play with bigger jets and needle positions can anyone help as i just dont know whether i have to much fuel or not enough.

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post #2 of 17 Old 10-01-2012, 12:33 PM
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Be grateful you aren't working on a carbed sportbike! They are a huge hassle to rejet. A single with easy access is infinitely preferable for learning about the finer points of rejetting.

First, are there any other modfications to the motor or exhaust? If not it just sounds like the air filter is (probably) less restrictive, which will require slightly larger jets and the needle raised one groove.

If you want to get it closer to spot on you will need to obtain a selection of main and if available pilot jets, and several spark plugs. What you need to do is install a main jet at least three sizes larger than what's in it at the moment and do a plug chop to check the mixture. To do this install a new plug and get it going as fast as you can in top gear with the throttle wide open. As soon as it stops accelerating pull in the clutch, kill the motor, and come to a stop somewhere safe. Let the motor cool enough to pull the plug and check the deposits on the insulator. They should be a light tan color with just a light dusting of black carbon at the base of the insulator.
-- If there doesn't appear to be any deposits or they are very minimal it is lean -- go up two jet sizes and do another chop.
-- If they are black drop one jet size, clean the plug or install another new one and go again.
Keep going until the plug looks a good tan color.

Now to press the lapels.
Run the bike up to a goodly speed in a middle gear and close the throttle.
-- If it backfires regularly the pilot (slow) jet is too small (lean), go up two sizes and try it again. If it just feels rough and backfires once when the throttle is closed go up one pilot jet size.

What the motor does at partial throttle will tell you what else needs to be done. If it stumbles at partial throttle raise the needle one groove and do another run. Usually one groove will make a significant difference in feel.

When you have all the jetting close to right do a lean idle drop and you're done. You will need to see what kind of adjustment it is first. There are two types: a fuel screw which will richen when turned out, and an air screw which will lean out when turned out. If you're not sure which it is turn the screw all the way in until it gently seats, counting the number of turns it took for future reference. Now remove the screw (careful here: usually there is a spring with an o-ring and steel seating washer -- don't lose these!) and look at the tip. If it's sharp it's a fuel screw and is turned out to richen. if it has a blunt tip it's an air screw and turns in to richen. Reinstall and gently seat it, then turn out the number of turns it was set to originally.

Now all you need to do is get the motor up to normal operating temperature and turn the idle mixture screw in the rich direction until to peak the idle speed, then continue turning until it starts to drop. Now turn it back lean until the idle speed peaks again and starts to drop, then back rich about 1/4 to 1/2 turn.

That oughta do it.

Enjoy!

Rob

If it has already been done, it is safe to assume it is possible to do it.
On the other hand, if it has not been done never assume it is impossible to do it.
------- Rob --------
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post #3 of 17 Old 10-01-2012, 12:59 PM
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yeah rob hit it spot on.

Start with the main, once you got that dialed or very close, then work your way down to pilot / fuel screw.

btw get some pics up of the cool lil bike!

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post #4 of 17 Old 10-01-2012, 01:05 PM Thread Starter
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Wow thank you Rob that is spot on i will get on it and come back as for the pics i think they should be attached to this post
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post #5 of 17 Old 10-01-2012, 01:08 PM Thread Starter
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I dosent look like i have done much but sofar i have rebult its little heart and built a battey box blown the tank over with a bit of silver made some flat bars and added the filter.

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post #6 of 17 Old 10-01-2012, 04:35 PM
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what a cool little bike! id love to have one similar for a project bike like this! good luck, post pics up as you go!

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post #7 of 17 Old 10-01-2012, 05:07 PM
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Great project!

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post #8 of 17 Old 10-01-2012, 06:48 PM
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+1 and Rob nailed it. He wasn't kidding when he said to be grateful it wasn't some 4 cyl sportbike. You can see how tedious the process can be lol. Have fun and keep us posted!

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post #9 of 17 Old 10-02-2012, 02:51 AM Thread Starter
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Arrre i have made an ajustment to the needle and all is well sort of untill i get to top gear then nothing it has nothing i will follow robs directions and see where i get to, its a shame but i am doing my dirext access soon and then my little cg will be finding a new home so that i may move on to a zzr 600 but i am having so much fun with it

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post #10 of 17 Old 10-02-2012, 08:42 AM
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Quote:
Originally Posted by Pvster View Post
+1 and Rob nailed it. He wasn't kidding when he said to be grateful it wasn't some 4 cyl sportbike. You can see how tedious the process can be lol. Have fun and keep us posted!
4-cylinder ANYTHING. My old gl1100 Oldwing with it's four carbs is going to be interesting, too....

Well, fire the engines! Spur this iron space-pony on!

"The Shadow"
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post #11 of 17 Old 10-03-2012, 07:37 AM Thread Starter
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If my experiance is anything to go by it will be most interesting bit great fun and really worth it can you post a picture of you bike

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post #12 of 17 Old 10-03-2012, 10:39 AM Thread Starter
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This may make me sound a bit daft but i am going to ask anyway i have been making adjustments but i havent untill now been looking at the plug and i have been at it for a week or so making an change each day. I have removed the plug tonight and indeed it was black with soot now here comes the question if the plug had become like this some days a go would the soot remain on the plug causing poor combustion even after the mixture had been made leaner, ie would it clear from black to light brown and if the plug is sooty how much will it effect combustion.

Sorry if this sounds a bit basic.

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post #13 of 17 Old 10-08-2012, 03:56 AM Thread Starter
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Yes i think ive cracked was a bit damp this morning so she was a bit jittery but its seems good

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post #14 of 17 Old 10-08-2012, 05:43 AM
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very very cool ride man.

Also, what's the big L on the fork for?

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post #15 of 17 Old 10-08-2012, 07:32 AM Thread Starter
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Hi mate the big L is because i have only a learner licence at the moment but i am taking my full licence over the next couple of weeks so a bigger bike is hopfully in the near future

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post #16 of 17 Old 10-08-2012, 09:15 AM
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Quote:
Originally Posted by munkeyharris View Post
Hi mate the big L is because i have only a learner licence at the moment but i am taking my full licence over the next couple of weeks so a bigger bike is hopfully in the near future
ah ok, cool deal. I think we should have graduated licensing here in the states for motor bikes as well. At the same time I'm really glad I didn't have to go through all that though, even though it would have been a lot safer.

Not to mention the fact that if they did it that way in the states we would get all the cool small bikes like the little VTR's and what not.

"A motorcycle is not just a two-wheeled car; the difference between driving a car and climbing onto a motorcycle is the difference between watching TV and actually living your life."
-2005 CBR 600 F4i
-2001 RC51 ** SOLD
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post #17 of 17 Old 10-29-2012, 03:04 PM Thread Starter
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Well the old girl is now running much better still in need of some tlc i have chopped the seat pan down and recovered the seat no the best job but i have had a go. Looking forward to getting her all painted up and i have now past my mod one big bike test and only my mod two to pass and then big bikes and the open road here i come.

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