Loud gear sound when revving?

I was having a similar problem, at one point it was just I had a too small jet, too lean in the first place, and part of it was getting the needle right. I dropped it to the lowest notch for the richest mix. I then got the bike warmed up, as frustrating as it can be, then turned my idle screw up a but to give it a couple hundred more rpms. Turn the idle air mix screw out from its deepest point very slowly. The rpm of the idle will get higher very slowly so give a second between 8th turns to hear the change. Get it to its highest rpm point and if you turn too far it will start to drop again.

Then turn the idle screw down until you get the nice low idle you prefer to have.

Ride it with the rich needle, if it doesn't help too much and you have no air leaks on the carb or the intake manifold then you'll need to get a bigger jet or leaner if you're working the other direction.

If the needle in its richest setting is too much and you bog down too much or 4 stroke, then bring the needle clip up a notch and try again.

The idle is more important than you think on these carbs so setting a bad idle or "falsifying" one with an enrichment or choke being engaged or partially engaged will affect the low (above idle) to mid rpm. This is simply because the idle orifice that holds the jet delivers the fuel through the main jet's orifice. If the idle isn't right it breaks up the system between mid and low rpm. These carbs don't use a pilot hole to deliver the idle fuel so there is a pilot "notch" on the bottom of the slide barrel that does the job of delivering the fuel via the main jet and needle chamber orifice.

If you have too many Japanese carbs laying around you can grab a barrel off the table that fits perfectly but doesn't have the notch on the underside and that can mess stuff up.

Out of curiosity if you take the air filter off and look into the carb is there a tube or barb thing that a plastic tube could fit on? It would be on the side closest to the bowl, and goes downwardish. There's basically 3 variants to this Cns design and yours could be 1 of 2.

Theres also a gasket related problem on the bowl for one of them. The oil gets channeled down to the bowl area, goes out a hole and in a little pocket, and out another hole, then sent to the jets via a few small drilled and plugged holes. If the gasket is damaged it lets raw fuel into the oil injection transfer little chamber area which then up and overs the main jet, feeding too much fuel to the point of delivery under the needle.
20161003_123457-1-1-1.jpg

The red area can be a damaged gasket letting fuel into that area with the green line. The green "oil path" is when the oil comes in and then gets sent up. The point of this was to make the oil ratio independent of the fuel and air ratio. It goes in to the bowl area, back up in that diagonal path to the main and idle jet holes. Air in there or excess fuel disturbs the jet settings and idle.

The blue line is the air idle mixture air path to the idle and main. When that air mix screw is unscrewed it uncovers the hole and lets extra air into the stream right above the jets, lowering pressure and mix accordingly.

This is why people can either love or hate these things, you got to set the jetting and levels from the idle up, or you get problems later on.

The other odd tube you see is part of the idle air mixture, it's the tube the delivers extra air to the idle jet with the other unmarked diagonal tube with the brass plug end,on the body of the idle jet orifice, the one basically in the center of the picture.

Once you get the hang of this carb you can basically install it on any small motors of a similar size and dial it in just as naturally. It works really nice in all conditions, and and changing the air idle for the changing weather helps with lessening the need to change idle jets often.

Good luck you'll get the hang of it in no time. Make sure you don't have any leaks anywhere else on the motor while you're at it.
 
Maybe there's something blocking fuel flow, because I pulled the hose off and turned the fuel on and nothing came out, and after shaking the bike a little, it started smoothly pouring out.
That's a little odd, I wonder if you have a hoard of rust settlement in your tank?

Maybe some as***le tossed sand in your tank while you were shopping?

Expect anything...
 
Maybe there's something blocking fuel flow, because I pulled the hose off and turned the fuel on and nothing came out, and after shaking the bike a little, it started smoothly pouring out.
Inside the tank there is a plastic and metal screen that threads into the fuel shut off valve that can get blocked.
I never use them.
An inline filter is all you need.
 
I have had to blow through the fuel hose back into the tank before simply because of rust that clogged that internal tank filter on the petcock.
Do away with that little filter and get a better petcock system at your local automotive parts store, the brass ones fit perfectly and allow for a great flow of fuel.
 
Maybe this can tell you what version I have. Here's a picture of the inside.
20170304_181144.jpg
 
Back
Top