Coolster 125 ATV won't climb

[xav1029]

I recently bought a Coolster 125 ATV for my son, and the only issue we have with it is that it won't climb ANY hill at slow speeds or from a stop. The quad is auto with F-N-R. Once up to speed in F, it does great. However, even on the smallest grades (ex slight incline driveway in Florida) it will NOT climb at super slow speeds or from full stop. The weird part is if I throw i in reverse, it can conquer any hill. Almost like forward and reverse are backwards.

Any ideas what could be causing this? Appreciate any help.

[Douglass]

Any idea what gearing it has? I have a 2017 Coolster 125cc with the same transmission, and it does ok when the throttle is limited. Reverse has a noticable amount of low end compared to the forward gear.

[Al]

Get a smaller front sprocket on eBay. 13 tooth or 12 tooth. It will your house down

[xav1029]

Ordered a smaller sprocket given that that a $10 and 10 minute fix. I'll let you guys know how it goes

[Douglass]

Ordered a smaller sprocket given that that a $10 and 10 minute fix. I'll let you guys know how it goes

Just a heads up, you will probably need to buy smaller allen head type bolts for the sprocket. Depending on the chain size, and that sprocket is smaller sometimes the chain will hit the bolt head.

You will need to grind down the keeper, and you might also need to grind down the side of the allen bolts too. If you have a grinder its easy, it will just be a little tedious.

Here is a picture of the bolts that have been ground down. You dont need to buy these, as you can buy the bolts from lowes or home depot for a few bucks. It is just for illustration.

https://www.whygostock.com/modified-...ront-sprocket/

[Darth Racer]

That link is for a 530 Sprocket on a 200cc engine. It might not be the right size for the Coolster 125. Different engine. Different series.

I think this is the right Sprocket Retainer for the 125cc https://www.whygostock.com/sprocket-...ao-and-others/

$10 Cheaper too.


Never mind... misunderstood the post... was just for illustration.... My bad

[xav1029]

Just took the quad apart. It already has a 13T in the front, 45T in the back. Should I really try a 12T up front? The problem is only in F and from full stop or extremely slow speed on any slight incline. Is there some type of clutch/tranny adjustment?

[david3921]

Originally Posted by xav1029

Is there some type of clutch/tranny adjustment?

Yep. Check post #5 from dirtbkr188 here;
http://chinariders.net/showthread.php?t=21934

[Douglass]

Just took the quad apart. It already has a 13T in the front, 45T in the back. Should I really try a 12T up front? The problem is only in F and from full stop or extremely slow speed on any slight incline.

You have the same gear ratio as mine.


By changing the front sprocket by tooth would be the same as adding four teeth to the rear sprocket. It changes the ratio from 3.46 to 3.73, so you should notice some improvement. It will also reduce the top speed. This style transmission is definitely a compromise compared to a CVT style transmission. I am really considering swapping a 3 speed w/reverse semi auto engine into the Coolster in April.

Douglass

[xav1029]

This is very frustrating. Granted I just bought this to put around our yard (5 acres), it still does not work right. I checked the clutch adjustment, and it was right where it should have been. I'll order the modified hardware to do the 12T swap and see if that helps.

Another issue is that if I punch the throttle even once moving, the quad bogs. I already tried adjusting the air/fuel mixture screw, but nothing has helped much. This isn't a huge issue though, because mostly put around with my 2 year old. If I can get the slow start from stop thing figured out, I'd be happy

[Douglass]

Another issue is that if I punch the throttle even once moving, the quad bogs. I already tried adjusting the air/fuel mixture screw, but nothing has helped much. This isn't a huge issue though, because mostly put around with my 2 year old. If I can get the slow start from stop thing figured out, I'd be happy

When I was running mine in I think the second run the carb crapped out. I have tried a couple different ones. To fix the bog you will need to try different needle clip settings. The stock carb will not have the additional slots to adjust the e clip, but you could try to put a small washer under the e clip to raise the needle.

This is the one that I currently have. It comes from China so expect it to take about 2-3 weeks. It will also require a new air filter. I am at 70ft elevation, air screw is about 1/2 a turn out, needle clip is in the second slot from the top.

Current Carb:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Air filter:
https://www.ebay.com/itm/EPA-Approve...UAAOSwGvhUEffa

Here is a direct replacement for what should be currently in the ATV. It worked better than the stock unit.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

[zackattack91]

12t in the front makes a noticeable difference. Might have to take a link out of the chain.

[mrboo]

12tooth sprocket is the way to go , did that to my tforce and a 28mm slip on exhaust and that woke it up

[xav1029]

Here's what it ended up taking to make it run acceptable:
12T front sprocket. Had to grind down the hardware
VM22 knockoff oversized carb from amazon. Had to rig it.

I feel that the quad now has perfect balance of power and speed for the single gear. It will actually climb at low speeds, even if rolling backwards. The carb is great too because it runs great at low rpm's and wide open. It used to choke wide open.

Thanks guys

[Douglass]

Glad to hear you got it.

VM22 knockoff oversized carb from amazon. Had to rig it.

Could you post a picture of how you installed this?