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Post by prodigit on Jun 24, 2013 22:09:45 GMT -5
Ok, so when my bike is cold, I need to pull the choke lever to the left.
This (I presume) will richen the mixture in the beginning.
Once the engine heats up, I have to pull the lever to the right (closing the choke). This will lean out the mixture (I believe; tell me when I'm wrong).
So, now, when riding on a hot engine, and going slow, the bike performs noticeably better with the choke pulled halfway open.
I presume this suggests in a lean idle jet? (it's a mikuni carburetor).
When I'm going all out on the highway, the bike performs better with the choke around 1/4th pulled out (so I have to move the lever 1/4th to the right, for it to run leaner).
In other words, my 127cc bike, probably has a 125cc carburetor mounted to it. I presume therefor that the carburetor was not rejetted, causing the idle jet to be way too small (running too lean).
The main jet seems to run less lean, so maybe that was adjusted a bit, but not enough.
Am I right in my train of thought?
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Post by scootnwinn on Jun 24, 2013 22:26:28 GMT -5
Your carb ks too lean if you have to run using the choke. The 2cc difference is not that much it is just poorly set up. Have you adjusted the the fuel mixture screw at all?
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Post by prodigit on Jun 24, 2013 22:33:34 GMT -5
yeah. Idles fine. Only thing is when the engine is hot, idle is up by at least 500rpm from a cold engine. I kind of like it to be able to tune into the engine's best performance, with the choke.
I know I need to change the jets or carburetor.
The 2cc is not 2cc. I think the 127cc is the actual cc's, while most 125cc's usually are lower, like 115-120cc or something. It would make for >10cc's differece
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Post by scootnwinn on Jun 24, 2013 22:49:33 GMT -5
Nope it wouldn't your talking a very small amount still. Anyway "tuning" with the choke is not what it was designed for necessarily there will be negative repercussions in the future I think if you don't take the proper steps now. Adjusting your fuel mixture will affect more than your idle. It is where you should start. Trust me give it a try.
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Post by prodigit on Jun 25, 2013 0:01:42 GMT -5
It's already set up to idle perfectly.
From here the choke performs linearly with the throttle.
Best idle with choke @ 1/2. I could turn it off, but the AF adjustment screw is already optimal I think..?
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Post by scootnwinn on Jun 25, 2013 0:07:16 GMT -5
Well good luck sounds like you have a better understanding of carbs than me. You don't even know what the choke does but you are going to tell me what the air fuel mixture screw does? You need to adjust it so it performs well at more than just idle. Do what you want Prodigit don't ask for help if you already know all about it.
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Post by prodigit on Jun 25, 2013 1:14:49 GMT -5
Not saying I do. However I already adjusted it that way.
I tried making it run richer at idle, but without much success.
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Post by jerseyboy on Jun 25, 2013 7:29:22 GMT -5
[replyingto=prodigit]prodigit[/replyingto]On a properly tuned motor you should NEVER need to use a choke to get things to run right.Run it without choke on a new plug and do a chop.Sounds like you need to up jet to me.
Good Luck...
Tom
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Post by scootnwinn on Jun 25, 2013 8:46:02 GMT -5
This may help you understand what is going on.  That's not your carb but they are all fairly similar I think what really needs to happen is the needle needs to be raised but, you said it is not adjustable. You should seriously consider shims. One way or the other you need to enrichen that portion of your throttle range. The mixture screw is the easiest way to do that... You can also restrict air flow to the same end. There is some chance the carb is bad or dirty... |
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Post by gitsum on Jun 25, 2013 10:39:30 GMT -5
After the engine is warm, you should never need to run with the choke open. This indicates a lean condition.
If the idle and 1/4 or less throttle runs better with the choke partially on, you need to adjust the fuel mixture richer or switch to one size larger pilot jet.
For 1/4 to 3/4 throttle, raise the slide needle one or two notches or add a shim.
For 3/4 to WOT, switch to a larger main jet.
It's actually not quite as simple as that, but this will get you started in the right direction. It takes a lot of trial and error to get it perfect...
If your carb is faulty or not the correct size for the engine, it will never run right.
If the airbox/intake is too large for your set up, it will never run right.
You need to check for vacuum leaks and/or air leaks in the intake manifold and upstream towards the airbox, especially where the intake hose attaches to the carb.
These things are definitely possible when you buy a really cheap Chinese motorcycle/scooter...
I give you credit for still trying. I would have never bought it in the first place. But if I had, it would already be thrown out in the junkyard or landfill.
Just think, what if you would have applied all of these hours you've been working on this project to a temporary job or overtime at your regular job? With the extra money you could have made a much better purchase.
Was it worth it and did your really save any money?
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