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Post by Silar on Apr 29, 2015 19:27:49 GMT -5
Finally got my scooter running, and I've been playing around with different settings with the carb just to see what it would do. I want to make sure I'm not running into a too lean situation and cause my engine to overheat.
Here's my current setup:
50mm BBK
Cone air filter
18mm Kei-Hin carb
#95 main jet
Needle clip at middle position
Idle Air Screw pretty well optimized for the best running idle
Blue performance CDI
All this is new as of the past week or 2.
With this setup, the engine takes a couple cranks to get up and running. Seems to idle fine, but if I blip the throttle to about half and let it go, it goes up in speed, then drops and dies. Almost like I've got a too rich condition.
If I put in the #90 main jet, set the needle clip to the top position (more lean), and start the scooter, it seems to like that better. Starting is much more responsive and I can blip the throttle to rev it like before to about half and even the engine is much more responsive and drops back down normally without dying.
I'm trying to avoid causing burnt valves, or ring issues, but this seems weird. Carb float and valve seems to be working fine and I have the float properly adjusted. I'm getting ready to pull the plug out and check to see how it looks, but when I checked it before it looked a bit rich...
I've seen where guys are putting 20mm carbs or more in their BBK's so me having an 18mm makes me also wonder if anything larger is just too much.
Any thoughts?
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Post by Silar on Apr 29, 2015 20:03:24 GMT -5
Maybe I jumped the gun... This is with a #95 Main Jet, needle clip at bottom (most rich) position. Idle is currently at about 2200rpm. Anyone want to diagnose my plug?  I'm guessing it looks pretty okay. Any other reason why the scooter would die as it drops down when I just rev it?   |
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Post by Upgrayedd on Apr 29, 2015 20:07:45 GMT -5
ahh so wih the 95 when you blip the throttle it comes back down and dies. does it drive okay with the 95 main in, and just an idle issue?
but with the 90 in it comes back down and idles. sounds like its a bit rich on idle, with the 95 especially. but i am not sure how much of that is due to the main jet vs the fuel enrichment screw / idle setting.
if you are idling ok and then give it gas for a second and when letting off gas the idle lopes (drops down) before coming back up, usually i take that as a sign of being rich up above idle. and if when letting off after gas for a bit if the idle hangs high, i take that as a lean up top sign.
ive never encountered a hanging high idle after just second of gas... that one has only shown itself to me after riding a bit, at least 10-15 seconds or so. like stopping at an intersection and the idle stays higher for a few seconds before tapering off and down to normal, thats a sign of lean somewhere up above idle.
no sweat youll get it. these little carbs are so much more finicky than the larger displacement bikes ^ ^
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Post by Silar on Apr 29, 2015 20:14:38 GMT -5
i think you might be lean on the main jet. i'm running an 85 main in a 47mm bore with mostly stock airbox. Hey Upgreyedd! Really? I was kinda wondering that. I'm starting to think about putting the stock airbox back on just to avoid any issues. Could there be a chance that I need to go up a step in my pilot jet also? |
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Post by Upgrayedd on Apr 29, 2015 20:19:45 GMT -5
i think you might be lean on the main jet. i'm running an 85 main in a 47mm bore with mostly stock airbox. Hey Upgreyedd! Really? I was kinda wondering that. I'm starting to think about putting the stock airbox back on just to avoid any issues. Could there be a chance that I need to go up a step in my pilot jet also? idk this ^ was based on my misreading your original post. i think you may be rich somewhere in there. but i am not sure if you are rich on main, it could be in the jet needle clip setting, fuel screw, etc. sorry about that  i am sometimes not at my best |
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Post by Silar on Apr 29, 2015 20:20:57 GMT -5
This exactly: "if you are idling ok and then give it gas for a second and when letting off gas the idle lopes (drops down) before coming back up, usually i take that as a sign of being rich up above idle."
I've got the #95 in and have the needle clip set to richest and the needle may be my problem. I'll start taking it back to middle and lean to see how that does.
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Post by humanshield on Apr 29, 2015 22:06:58 GMT -5
Have have pretty much the same setup and I'm running a 90 MJ. Anything more caused it to run like crap. Stock airbox with a unifilter green custom cut filter element. 6.5 gram weights.
Pulls nicely to about 35 then can manage 42 but never got above 42 on level ground, no wind.
Oh, removing the snorkel made a feelable difference on mine.
I would love to try a 20mm carburetor, except they don't exist in the traditional GY6 50cc style. Not a REAL 20mm carb anyway. I have one with a 20mm butterfly valve and it's STILL an 18mm carb.
The needle position was very touchy on mine. I keep meaning to document the jet sizes and needle settings every time Im in there and I forget....every time :-(
Anyway, I can tell what other people have in their scooters by how much I outrun them (or they outrun me) lol
I walk away from 49cc scoots hands down. Juuuuuust barely pull away from 72cc scoots.
I expect that gap to widen once I install my big valve head.
May have to use a carburetor off a different application to get a REAL 20 or 21mm carb.
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Post by 90GTVert on Apr 30, 2015 7:24:21 GMT -5
You should be working on one thing at a time IMO. If you're swapping the jet and the needle at the same time, stop that. I usually set the needle toward the center or slightly rich and then work on the main jet only with WOT runs. I don't touch the needle until I figure out what main jet it likes for WOT. Then I work on other systems. I do usually adjust the idle mixture as I go so it idles well enough that I can not worry about it dying on me. All of this should be done under load  BTW. I have heard some people trying to tune simply revving on the center stand but IMO that's not effective other than for idle mixture adjustment. It will act different under load than free revving on the stand. |
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Post by Silar on Apr 30, 2015 7:44:44 GMT -5
Thanks. I do tend to try and do multiple things at once which usually bites me in the end.. Like this one. I had it running great with the stock air box with no internal or external snorkel, but I knew I was going to get the cone filter so I up jetted to #95. And set the needle to rich to try and compensate, even before testing, but I think it was probably more of a minimal change on air flow and would have been fine where the needle and jet were with the semi open air box. Probably not much of a change.
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Post by Silar on May 1, 2015 7:32:27 GMT -5
Switched back to the #90 main jet and put the carb needle clip position to 1 step lean above middle. Currently running with the aftermarket cone type air filter. Throttle response is crisp and snaps back to idle with no hesitation or bog. Pretty darn responsive. Something I noticed and not sure if anyone else has, is I was originally running the factory airbox with the internal and external snorkel off with the #90 jet. Using the #90 jet with the cone air filter my engine seems to run about the same which is pretty darn good. I think what was happening, is as I was riding, air was being pushed into the open port where the snorkel was, inducing extra air volume into the carb. With the cone filter on, it is more open I am sure, but not in the path that air can be forced in, so total air volume seems to be about the same. I was thinking that I would have to upjet, but that may not be the case.. I'm going to ride it some today to see how it does. Here's the air filter I'm using. I pretty much will be riding this scooter only on pavement and in dry conditions..  |
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Post by Silar on May 1, 2015 18:56:06 GMT -5
Nevermind. After some tweaking it seems that my bike just doesn't like that aftermarket pod filter. I've switched back to using the stock airbox (with external snorkel, minus the internal snorkel and the 4 hole attachment) with a #90 jet, right at 2 turns out on the air/fuel mix screw, 1 step slightly lean than middle on the diaphragm needle clip. Seems to run strong, but it still almost seems just a little rich and bogs just ever so slightly on WOT. Also after a bit, when throttle is released and it gets down to idle it'll die. Almost like all air is cut off. It only does this occasionally. Makes me think it's giving too much gas still, or maybe I still need to go a bit leaner on the needle clip. Makes me want to try a #85 jet to see how that does.. but.. I'm exhausting everything else first before I switch jets again. I'm trying to take your advice Brent! Any thoughts? |
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Post by Elektrey on May 1, 2015 19:24:25 GMT -5
I used to use an air filter like that, but for whatever reason it just hated it. Took me too long to single out the air filter. It would act fine one day, and super rich the next.
Ditched it and am using a piece of cloth zip tied around the air filter connection on the carb.(at least for now)
I am running an 80 Main jet with needle on leanest position with a 19mm carb on a 70cc if that helps. Plug looks great, a tan color.
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Post by Upgrayedd on May 1, 2015 20:06:51 GMT -5
Nevermind. After some tweaking it seems that my bike just doesn't like that aftermarket pod filter. I've switched back to using the stock airbox (with external snorkel, minus the internal snorkel and the 4 hole attachment) with a #90 jet, right at 2 turns out on the air/fuel mix screw, 1 step slightly lean than middle on the diaphragm needle clip. Seems to run strong, but it still almost seems just a little rich and bogs just ever so slightly on WOT. Also after a bit, when throttle is released and it gets down to idle it'll die. Almost like all air is cut off. It only does this occasionally. Makes me think it's giving too much gas still, or maybe I still need to go a bit leaner on the needle clip. Makes me want to try a #85 jet to see how that does.. but.. I'm exhausting everything else first before I switch jets again. I'm trying to take your advice Brent! Any thoughts? are u setting the fuel screw by finding the spot where it idles fastest+smoothest? mines set abuot 1/8 of a turn toward rich from there. |
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Post by Silar on May 2, 2015 8:09:20 GMT -5
Nevermind. After some tweaking it seems that my bike just doesn't like that aftermarket pod filter. I've switched back to using the stock airbox (with external snorkel, minus the internal snorkel and the 4 hole attachment) with a #90 jet, right at 2 turns out on the air/fuel mix screw, 1 step slightly lean than middle on the diaphragm needle clip. Seems to run strong, but it still almost seems just a little rich and bogs just ever so slightly on WOT. Also after a bit, when throttle is released and it gets down to idle it'll die. Almost like all air is cut off. It only does this occasionally. Makes me think it's giving too much gas still, or maybe I still need to go a bit leaner on the needle clip. Makes me want to try a #85 jet to see how that does.. but.. I'm exhausting everything else first before I switch jets again. I'm trying to take your advice Brent! Any thoughts? are u setting the fuel screw by finding the spot where it idles fastest+smoothest? mines set abuot 1/8 of a turn toward rich from there. I am. Originally, this carb had me fubar'd up thinking the idle screw was an idle/air screw. I may remove my rear panels again so I can troubleshoot this thing easier. I pulled the plug the other day with the panels on and that was a chore! |
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I'm guessing it looks pretty okay. Any other reason why the scooter would die as it drops down when I just rev it?
i am sometimes not at my best
BTW. I have heard some people trying to tune simply revving on the center stand but IMO that's not effective other than for idle mixture adjustment. It will act different under load than free revving on the stand.