3150 DX2 stutter/bog at part throttle.
 

I have a little bit of time on my DX2 now and it has always had a slight stutter and bog at part throttle. It clears out at full throttle. I also have to crack the throttle slightly when starting. I am thinking it may be set too lean. I guess I am going to drill out the mixture screw plug and try to tune it. Am I on the right track?

-Eli

I'm lazy so here is a cut and paste I found awhile ago on CV carb tuning. George (original poster) is working on 150 CC scooters which share the same power plant/carb as your Coolster.

How's everyone doing ? There are a few carb tuning threads out there , but I'd like to post a quick carb tuning tutorial. First here is a pic (Picture #1) of the most common unsealed150cc gy6 carb. This is your typical 24mm keihin carb. Is this a copy or is this the real deal ? To be honest we just dont know for sure. The copies have become so good that not only do they look good , but the work just as good also.

Here is a pic of the idle adjustment screw. (Picture #2)

And here is a pic of the air fuel adjustment screw. (Picture #3)

This tutorial is focused of tuning your carb with the air fuel and idle screw. Remember jetting may also need to be considered , along with vacuum leaks , if you cannot get the carb tuned correctly with these steps.

The first thing you want to do is start your scoot , after your scoot is warmed up and the autochoke closes of the extra fuel , you will next turn the idle screw clockwise so your rpms are a little higher then recomened, which would be anywhere from 1800-2000 rpms. Now what you want to do is turn the air fuel screw clockwise until the rpms begin to drop off. Next turn the air fuel screw counter clockwise until you get you highest rpms possible " be very careful , if your rpms begin to rise too high the clutch may start to engage , and the scoot could take off on you !! " to avoid this , you can back the idle screw off some by turning it counter clockwise dropping the rpms back down near 2000 , then you can continue turning the air fuel screw to obtain the highest rpm possible. Remember you only need to back the idle screw down IF you notice the rpms getting too high and the clutch wanting to engage. Finally , after obtaining the highest rpm with the air fuel screw , you will now want to use the idle screw to set the idle rpm back down to around 1700 .

After you have the carb tuned in properly, you may need to adjust the air fuel screw according to the weather. For instance , if the temp drops 30+ degrees , you may need to retune the carb due to the cooler dense air. These setups are very touchy when it comes to the drop in temps from season to season.
Hope this helps. Thanks , George

I drilled the plug out of my mixture screw and got it to run a bit better. I think there may be junk in my pilot jet. I'm going to pull it and clean it out when I have time. The main jet seems to be fine because it runs great at WOT.

-Eli

So.... how am I supposed to clean/check the jets when there is no visible way to remove the bowel? I might just buy a good replacement carb. What is a direct replacement?

-Eli

You can get the bowl off by removing the screws. A google search will show you the various methods. Most use a dremel type of tool and either slot the screws for removal with a screw driver or notch each one and work it out with a punch. I suppose you could drill a hole and use a scew extractor also.

You can cut slots in the screws with a hack saw. That's all I did to get access to the jets. If yo plan on replacing the screws you can just drill the heads off and remove the rest of the screw with vice grips.

Man, wish I had seen this earlier. It was fun getting that carb off, only to discover the safety screws...lol. I dremeled and used a flat blade and then replaced the screws with Allen cap screws.
I didnt find anything in my carb either, very disappointed. I was having the same issue. In one of your other threads, I mentioned that these are super lean so as to be sold in California. Your part throttle bog should go away once warmed up, but if you are like me, and want it working right, just adjust the carb like stated above and that bog will be gone. It should also start better, but I too still have to blip the throttle once in a while.
Also, learn from me, and grab a grease gun and fill the zerk that's on the swingarm pivot. I didn't know it was there and wore out one of the bushings prematurely. My wife's has been fine as I've been greasing it since day 1