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Post by xxmindkillrxx on Apr 30, 2015 12:51:04 GMT -5
So I just got my scooter back from the shop where they installed a new head, the old one was leaking compression. Well I managed to ride it home but it was running kind of funny like the air/fuel mixture wasn't correct. I need some advice on adjusting the carb as I've neved messed with one too much. The scooter is a 50cc GY6 with a uni air filter. I tried adjusting the air/fuel screw for a little more fuel but whenever I would hit the throttle the scooter would rev up and pretty much stay at high rpm's for a bit before slowly coming back down. So I messed with it some more and got it to where the scooter would bog down and almost die when I throttled it like it was getting too much air. I could really use some advice as I'm not too savvy on tuning a carburetor correctly. If it helps any its a Keihin carb and its already been cleaned twice, by me and the shop. Any help is appreciated.
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Post by geh3333 on Apr 30, 2015 14:55:32 GMT -5
Sounds like a possible leak somewhere. When it takes time for the rpms to drop after giving it throttle , it could be a vacuum leak
For carb tuning it is very simple . first start the scoot , let it warm up . after it warms up I usually turn the idle screw so that the scoot idles at 2000 rpms. Next what u want to do is turn the air fuel screw to the right slowly . pause for about 20 seconds after every 1/8 to 1/4 turn. Keep this up until the scoot starts to hesitate like its going to shut down. Next turn the air fuel screw back to the left , again pausing after each turn . keep this up until u get your highest rpm . after you hit the highest rpm you will want to then turn the idle screw back down to around 1700 rpms .
Just be careful when hitting the highest rpms with the air fuel screw . you don't want the rpms to go up so high that the clutch engages and the scoot takes off on you. If the rpms seem to be getting too high , stop and turn the idle screw down some and then continue with the air fuel adjustment.
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Post by steve on Apr 30, 2015 17:47:19 GMT -5
Definitely sounds like you have air leaking somewhere. The air/fuel screw is probably not going to fix your issue. Start by checking the hoses coming off of the nipples of your intake manifold. You can spray them with carb cleaner, or WD 40, and if it bogs, you know where the leak is. They could have knocked one of the hoses off putting your head on, and forgot about it.
Question: Does it sound any different? Louder?
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Post by xxmindkillrxx on Apr 30, 2015 20:40:48 GMT -5
Ok so I also failed to mention the scooter does have a BBK (Sorry). I did check all the hoses and vacuum lines but no leaks. As far as it sounding any different, it just sounds a tad louder due to the high flow filter I'm guessing. I've got it directly attached to the carb. I managed to adjust the carb to where the scooter is driveable but the only thing I can't really fix is when I first take off if I give it full throttle it will bog down and want to die. I kinda have to gently rev it a few times before taking off to get it to take off without it bogging. I'm thinking it's just not getting enough fuel. It also still wants to idle a little funny, sometimes a little high, sometimes a little low. Should I try upjetting my carb? Or maybe just buy a bigger carb?
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Post by geh3333 on Apr 30, 2015 21:06:04 GMT -5
Ok so I also failed to mention the scooter does have a BBK (Sorry). I did check all the hoses and vacuum lines but no leaks. As far as it sounding any different, it just sounds a tad louder due to the high flow filter I'm guessing. I've got it directly attached to the carb. I managed to adjust the carb to where the scooter is driveable but the only thing I can't really fix is when I first take off if I give it full throttle it will bog down and want to die. I kinda have to gently rev it a few times before taking off to get it to take off without it bogging. I'm thinking it's just not getting enough fuel. It also still wants to idle a little funny, sometimes a little high, sometimes a little low. Should I try upjetting my carb? Or maybe just buy a bigger carb? You def have an air leak somewhere. Everything you mention points to a leak . the variating idle and the slow throttle drop. Your leak could be at the manifold , or between the carb and the manifold. Its not just the hoses you need to check . you may need to use some gasket maker between the head and the manifold . you will need to find the problem and then go through the carb tuning steps again . |
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Post by xxmindkillrxx on Apr 30, 2015 21:33:32 GMT -5
Well the slow throttle drop stopped after messing with it some more and attaching the air filter directly to the carb. The guy who had the scooter before me had the throttle cable pulled too tight to where the butterfly valve was staying too open during idle so I fixed that. I'm gonna go ahead and double check my intake manifold and around that area for any air leaks tomorrow. I'm also gonna order a 20mm carburetor from scrappydog just to help a little with performance and I guess take it from there.
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Post by geh3333 on Apr 30, 2015 21:55:43 GMT -5
Well the slow throttle drop stopped after messing with it some more and attaching the air filter directly to the carb. The guy who had the scooter before me had the throttle cable pulled too tight to where the butterfly valve was staying too open during idle so I fixed that. I'm gonna go ahead and double check my intake manifold and around that area for any air leaks tomorrow. I'm also gonna order a 20mm carburetor from scrappydog just to help a little with performance and I guess take it from there. What size is on there now ?, 18 or 19 ? |
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Post by JerryScript on May 1, 2015 4:24:09 GMT -5
No need for a larger carb necessarily. What size main jet are you using, and did you up-jet when the BBK was installed?
A larger main jet and a needle clip adjustment should fix your bogging (assuming there are no air leaks).
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Post by xxmindkillrxx on May 1, 2015 11:28:31 GMT -5
Ok so I'm getting ready to test for air leaks in just a few but I wanted to update as I just found out the carb is already a 20mm, so apparently its already been upgraded. I'm not sure of the size jets in it though. Is there any way to tell what size they are? I'll update in a bit as to whether I find any air leaks.
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Post by xxmindkillrxx on May 1, 2015 12:35:40 GMT -5
So I checked for any air leaks and came up with nothing, I blasted starting fluid all around the carb and intake manifold but didn't hear a bit of difference in the idle. I did manage to record a video of how its acting though so you guys can see it for yourselves.
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Post by scooter on May 1, 2015 15:29:01 GMT -5
Ok so I'm getting ready to test for air leaks in just a few but I wanted to update as I just found out the carb is already a 20mm, so apparently its already been upgraded. I'm not sure of the size jets in it though. Is there any way to tell what size they are? I'll update in a bit as to whether I find any air leaks. They are usually marked on the top or side.  |
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Post by geh3333 on May 1, 2015 17:50:53 GMT -5
Many of the jets that come with these carbs are not marked.
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Post by xxmindkillrxx on May 3, 2015 17:38:14 GMT -5
Yea the carb I have is a Keihin clone and has the longer style jets. Anywho, I rode it a bit this weekend and it seems to run a bit better after about 15 minutes of riding once it's warmed up. The bog isn't quite as bad but it will want to idle pretty low. I'm gonna set the idle a little higher and see if it helps any.
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