50cc GY6. Pod filter. Should I upjet?

[deejais]

Project I’m working on now is an’02 Honda Meteo. I took off the air box, intending to use a pod filter instead. A Honda-smart guy I know gave me the lowdown on upjetting, since there will be considerably more air in the carb without the airbox.

Makes sense and parts are ordered, but it’s made me think about my OTHER bike, with a brand-new 50cc GY6 engine. I also took off that airbox, installed a pod filter, and did not upjet at all. Carb is stock, and after two months of flawless riding, it FEELS fine to me, starts, idles, and runs nicely.

So should I have upjetted the GY6? I didn’t know anything about it a couple of months ago. Honda guys suggest 85/38 for the Metro, but what about my Chinese carb? Possible I’d see some performance if I stuck some bigger jets in?

[aeroxbud]

It's probably running lean. You should be able to check the plug and get an idea of how much.

[deejais]

Nov 11, 2020 7:17:07 GMT -5 aeroxbud said:

It's probably running lean. You should be able to check the plug and get an idea of how much.

I'll give it a check.  Thanks.

Meantime, I got the old Honda started today, its first time running in at least three years.  Spent the whole morning breaking down and deep-cleaning the well-varnished carb.  Soaking/blowing out the jets, un-sticking the slide piston and needle, all of which were gummed up hard.

Once I started it, and got it to idle, I just let it run to get warm and just run on the stand for the first time in so long.   As it sat there idling, without me touching it, it would rev up with the wheel turning quite fast, then it would rev down and idle properly.  It did that off-and-on for about 15 minutes, up and down, never really settling on a nice idle.  The airbox is gone, the pod filter is on, and the carb has the stock jets.  (I think 72/35)

I wonder if the rough running and bad idle is from the too-small jets, or just from finally running after several years.   The only adjustment on this carb I could see is the throttle adjustment, I didn't see a mixture screw like I see in most carbs.  Maybe this mixture screw is inside the carb.

[90GTVert]

4Ts are somewhat forgiving on jetting. That said, you may be able to find more power and increase engine life with some tuning.
www.49ccscoot.com/faq/carbtune.html


Surging could be a lean condition, but it may be an intake/vacuum leak. Before you worry about the tune, check for leaks. The most obvious is to look it over. Make sure you don't have a cracked intake, you don't see any fuel residue around a gasket and that sort of thing. Then you can check with it running to see if it responds when you either mist areas where it could leak with water (fine mist, spray bottle) or use an unlit propane torch near the intake tract. If those things change the idle, then it's leaking. Don't spray either on the pod filter. Just check areas around the intake that should be sealed off from the outside.

[deejais]

Thanks

[GrumpyUnk]

Many times an idle that climbs high and then drops off is set right at the lower limit of the intermediate circuit. It becomes unstable because it is at the lowest edge of being 'intermediate' and it doesn't mix very well using that circuit. I suspect your 'idle' circuit is not adjusted properly or is plugged or you have the throttle plate set a bit too high. If you have an idle mixture screw, it may need cleaning if you haven't touched it, and if it is clean, may need to be adjusted along with closing the throttle plate a bit. A clogged pilot jet will also cause the same thing.
tom

[wiscootsin]

If it sat that long I would clean the carb again after running it for awhile the first time. I've discovered new junk in similar circumstances.