125 Coolster GY6 to predator 212 swap

[JustBeginning0124]

I know it’s not a go kart necessarily but the idea is the same and I don’t know where else to ask. Buddy of mine swapped a Coolster 125 GY6 motor out for a predator 212, the 4wheeler will move with no weight on it not fast but will move, as soon as you put weight on it, it struggles. I don’t know what’s causing it but there’s a loud backfiring when trying to accelerate and if you push full throttle it wants to die out. Now he thinks it could be the jets in the carb but he’s already bored them out as much as he could and it’s still doing it. Any advice would be much appreciated, I have a video of the problem as well as a picture of the TC/Chain sprocket set up. But the video won’t let me post on here I could email somebody the video if need be though

 

[Rat]

I know it’s not a go kart necessarily but the idea is the same and I don’t know where else to ask. Buddy of mine swapped a Coolster 125 GY6 motor out for a predator 212, the 4wheeler will move with no weight on it not fast but will move, as soon as you put weight on it, it struggles. I don’t know what’s causing it but there’s a loud backfiring when trying to accelerate and if you push full throttle it wants to die out. Now he thinks it could be the jets in the carb but he’s already bored them out as much as he could and it’s still doing it. Any advice would be much appreciated, I have a video of the problem as well as a picture of the TC/Chain sprocket set up. But the video won’t let me post on here I could email somebody the video if need be though

Sound like it's excessively rich, sparky color will confirm.
Pull the plug, if it's black and sooty then it's on the edge if not being able to run at all.

Jet boring should be a last ditch effort hail Mary fix because it sound like a final drive ratio problem as far as the motorvating part goes and the sprocket in the pic looks too small compared to those big mud tires.

You typicaly need a 6:1 drive ratio to have things work without smoking the belt... if it's the chinese belt that came with the TC instead of a Genuine Comet it's already toast and there's no fix without getting a new belt. As is it sounds like the jets need replaced because he doesn't really know what he's doing at all.
10/60= 6:1
9/54= 6.22:1

 

[JustBeginning0124]

Well you’re right about that he does not lol neither do I when it comes to this. He did however attempt to compensate for that by buying a larger sprocket but the hole alignment was off the holes that were in it were too close together to drill in between them. I will let him know this though thank you

 

[panchothedog]

I know it’s not a go kart necessarily but the idea is the same and I don’t know where else to ask. Buddy of mine swapped a Coolster 125 GY6 motor out for a predator 212, the 4wheeler will move with no weight on it not fast but will move, as soon as you put weight on it, it struggles. I don’t know what’s causing it but there’s a loud backfiring when trying to accelerate and if you push full throttle it wants to die out. Now he thinks it could be the jets in the carb but he’s already bored them out as much as he could and it’s still doing it. Any advice would be much appreciated, I have a video of the problem as well as a picture of the TC/Chain sprocket set up. But the video won’t let me post on here I could email somebody the video if need be though

 

[panchothedog]

You might have to have the new sprocket professionally drilled to match the hub that is currently on the drive axle. It can be done at home, but only if you have the ability to keep it perfectly centered and concentric. Before paying a machine shop to drill it, make sure that it is at least a 60 tooth sprocket and is the same pitch ( uses the same size chain ) as is on the torque converter. As posted above by RLS, a 9 tooth X 54 tooth will also work. This is so the kart will accelerate and drive properly once you get the engine figured out. Sounds like a NEW STOCK carburetor might just be your best friend.

 

[Rat]

Well you’re right about that he does not lol neither do I when it comes to this. He did however attempt to compensate for that by buying a larger sprocket but the hole alignment was off the holes that were in it were too close together to drill in between them. I will let him know this though thank you

4bolt sprockets are fairly common and therfore relatively cheap.
The mistake he made was doing things without thinking first, and lacking adequate mechanical skills... by definition that makes him a dumb@ss.

The correct way to do that would have been to measure the bolt holes across from each other in the sprocket carrier, then measure the other two to make sure its the same and then order the correct sprocket the first time by having the bolt pattern already.