First question: what mods are on it?
The carburetors on the ASW machines are their weak spot. There is no one setting that works for all machines. Each machine will need their own settings. It seems to me that 1 out of about 5 of these machines has a crappy carb on them.
Here's the kicker: All of the 150cc GY6 carbs are not created equally. About the only thing consistent is the fact that they will mount from machine to machine.
For example, I have a brand new helix here (the one for sale in my for sale thread). It had the second carb in a year that I have seen that is just a piece of crap carb. I replaced it with another carb (new) that was intended for a scooter. As expected, it had a very lean main jet, a 102, in it and it has a 35 pilot in it. The stock Helix carries a 114 main and a 34 pilot. Experience shows me that the 114 runs very lean in these so I always suggest to put about a 125 main in it in stock form to keep them from running lean. There are reports of engines blowing and typically it is because of this lean running.
Now...you would think that all I would need to do with this new carb is swap my jets over, right? No! I put the 114 main in it and left the 35 pilot. Ran it, checked the plug and it was running on the fat side (rich). That's with the same 114 that typically will run lean in the carbs that come factory on the Helix. What I wound up doing was taking the 102 main and running a drill bit through it that was smaller than the 114 and my guess is that the jet is now about a 110 or so. Guess what. It created one of the nicest looking burns on the plug that I have ever seen. It likes the 110 in the carb that was made for a scooter.
What this whole thing does is confirm that despite the outside appearance of all GY6 carbs looking the same, the internal porting can be (and usually is) very different among different manufacturers.
Now..that said, this buggy is one of the nicest starting buggies ever as well. As a spectacular idle. Better than our personal Helix. Doesn't matter if it is cold or hot, it is rather nice.
On our personal Helix, I think I have a 128 in it with the only mod being the CDI and it burns beautifully. If I ran that 128 in this scooter carb, it would never run. However, with ours, you typically have to give it a little gas when you start it and if you take it out for a wide open run and then come to a stop, it may stall out on you if you don't lightly feather the gas a little bit. I think this has to do with the bowl level being lower when we stop due to the long high speed run. Don't know for sure, and really don't care. I expect it to act like that under those conditions. In fact, knowing what I know about the carbs ASW uses,, it doesn't do anything that I don't expect it to do.
For your particular problem there are a few things that you should know that may better help you understand what it is supposed to be doing. A carb is made of many different circuits. Idle circuit being one of those. Your pilot jet handles most of the task of idle and your main butterfly valve works with it. Remember that your needle (the one that sits in the main jet) doesn't really start opening until you are under a heavier load. The butterfly valve that your throttle is connected to is providing the air, and the pilot jet providing the fuel (both required for an engine to run). As you open that butterfly valve more (i.e. step on the gas or turn your idle screw higher), you will eventually get to a point where the needle will start raising out of the main jet and some fuel will be provided by that main jet. For you to correctly set your idle, idle settings need to be made below the point where that needle starts raising out of the main jet.
If you have any kind of blockage in the idle circuit, be it in the pilot jet or the ports that the fuel runs through past the pilot jet, it's not going to idle. Some people wind up cranking up the idle screw which eventually will raise the needle out of the main jet and provide fuel and once you are at that point, your idle will be high..usually enough to engage the clutch. If you are getting that high to engage it, I question whether or not your idle screw is much too high. Just remember, you want your idle settings to be made below-the-bar (so to speak) of where the needle will start being raised out of the main jet.
All of tha said, you need to come up with a baseline. Some where to start. It typically will take two people because you want one person running the gas pedal and keeping it running until you find the sweet spot. Be forwarned that if you try to operate the throttle manually at the carb, you stand the chance of the cable coming off partially and raising the RPM's enough that the buggy will take off (don't ask me how I know).
Don't forget that the ASW machines have a nuetral position, use it.
There is an idle mixture screw and an idle screw. The idle screw is near where the cable connects to the carb. The idle mixture screw is on the left side of the carb (when standing behind the buggy and looking forward) and towards the front of that side. Some of them are capped off and that cap would beed to be pulled but since you have already tinkered with yours, I don't think that is a problem for you.
Take the mixture screw and turn it all the way in (click-wise) until it bottoms out and note the orientation of the screw slot. From this point I will turn that screw one and a half turns out. This is my baseline. I will have my helper start the buggy and slowly let off the gas. I will turn the idle screw up until the machine will idle by itself, even if it is a high idle. At this point, I now have control of the idle and I don't want my helper touching the gas. I will back off the idle screw till it either idles where I want it to or it stalls.
If it idles at an RPM that I like, I will move over to the mixture screw and turn it a half turn in. Your goal is to find the point in the mixture screw setting where it idles the best. If it starts barfing as I turn it in, I know I went the wrong way, I will then back it out a half turn at a time until it no longer is getting a better idle. Mind you, you may be having to make idle screw adjustments as well. If turning it out raises the idle above what I want it to be, I will back off the idle screw and then go back to the mixture screw and continue. You want to find the best idle point with the mixture screw and then no more than that point. So if at two and a half turns out it idles fantastic and at 3 turns out it idles no better, there is no point in keeping it 3 turns out, put it back at 2.5 and be done with it.
If the machine stalled when I turned the idle screw down, then I will go back to the mixture screw and go a full turn out (so now I will be at 2.5 turns out from bottomed out), turn the idle screw back up, have my helper start it and slowly let off and try again.
Now...if you find that it takes upwards of four turns out to get it to idle, that means your pilot jet is too small. You may be able to get away with it like that but I had one like that and the spring tension on the mixture screw was too little to hold it in place, and it fell out into never-to-be-found-again-land. At this point you would need to go to a 35 pilot jet and you'd likely find your mixture screw liking 1.5 turns out instead of 4.
With all of this said, remember that some carbs from ASW are simply duds. I have two of them sitting here that I use for spare parts. Just bad machining.
Hope this helps, tired of typing.
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