that guy from Canada

Most atv utv i recommend 10w40 oil, period, but make sure it is JASCO MA2 for wet clutches, motorcycle oil.

U can use regular oil but it will burn easy cause of wet clutch and glaze the clutch, causing slippage.

Welcome and cheers from the North

Body metal and pop rivets?

Ive used panels from old washer dryer or fridge as well.... 

That sux, probly just crappy plastic

If it only happens downhill engine braking, and riding the brakes stops it its simply a design flaw. 

If not i would take it back to dealer, could be something else, hard to diagnose unless i could actually test drive it myself.

Hmmm only thing i can think of is that if the rear driveshaft doesnt have a carrier bearing part way down it could be binding when off throttle, downhill under load. 

Other thought if you are decending steep and engine braking without dragging or using the actual brakes it can be the secondary loading up and banging around.

Do a test run on the second point see whats up, if braking helps just brake.

Ok is this a new or used unit?

Welcome!

Just a introduction to the offshore brand machines. 

They tend to be underpowered and high geared for heavy loads or work.

Be sure to use low range when working.

Also i suggest putting your cooling fan on a direct ignition relay, bypass temp sensor, quad is on fan is on for work. Or you can put fan on a switch, turn on in low range, but you can accidentally forget.

These tips will help prevent overloading or overheating the engine 

Cheers from Canada!

Does this happen in 2wd or 4wd or both

Is it that it has to actually cool off or is it that it simply has to sit a few minutes?

Boss audio has been around a long time... tested n true for a budget system. 

Its not the best per say but reliable yes.  Bang for buck best bet.

My opinion

You should never have "a couple of bad ones" pump is good or its not.

Likley you have another problem

Have you changed the inline filter?

Have you fully drained and refilled the tank with fresh fuel?

Have you cleaned or tested the injector(s)?

What Andy said is true.

Dollars to doughnuts, almost all chineese knock off ATV and UTV are simply underpowered and geared to high.

Clutch mods help but best just to use low range gear, be sure cooling system is all good however because you revs will be high and cooling is sub standard, many i have put cooling fan on direct ignition relay, bypass temp sensor, so its just on.

Likley yes high idle will cause it to grind when shifting, also if it has remote shift lever check the adjustment.

Most utv use a relay ignition powerd 

Look up in thread, try one hotter heat range plug than stock.

Ex: cr7hsa use cr6hsa NGK

Lower number is hotter

Is this electric UTV or a starting battery for gas

Your thought process is correct im just always simple first.

the spark plug cap on the plug has a built in resistor that can fail, system is..  coil, coil wire, cap, plug.

unless it us coil on plug 1 piece unit that goes straight on plug.

Either way if you have weak spark you will foul plugs.

2 stroke never run hotter plug to prevent fouling, engine damage will result. 4 stroke 1 range hotter wont hurt the motor. You could simply try that.

Should not be reverse thread.

Try an impact gun the vibration will help, also heat.

Higher octane fuel burns slower and prevents knocking and pinging. Also it tends to have a longer shelf life before it breaks down.

If your model is equipped with antiknock sensor you will find a noticeable performance increase with high octane fuel due to automatic timing advance to take advantage of the fuels burn time.

Regardless it never hurts to run higher octane fuel and for the amount powersports equipment burns price is really negligible. 

I try to run nothing but premium in anything but my truck... for both performance and incase it sits for a month or more.

You would have to do the research on axle fitment hubs etc.

Motorcycle doctor has most the microfiche.

Unless your worried ab9ut tearing up your lawn on sharp turns unlocking diff simply has more parts to break inside... just saying

Try to spin driven pulley shaft by hand and make sure transmission is in gear. 

With driven pulley installed you should be able to turn it by hand and "drive" the utv thru the transmission.

If not its possible the transmission is damaged.

Wouldnt hurt to just drain the whole fuel system and try fresh fuel.

Easy enough to do 

^^^^ check that first ^^^^

I would almost consider a new coil and the often overlooked spark plug cap.

Also as a 4 stroke it wont hurt it to try one hotter heat range plug.

Ex: dpr7ea use dpr6ea lower number is hotter

Ok so it looks like you have to just clean the spline better

Its hard to lign up

 Looks like you jeed a new primary however 

My only concern is that technically your clothing to a point IS your safety gear when using ATV UTV

Seen many people burn a leg on hot ATV exhaust in shorts or regret short sleeves and no gloves if they wipe out.

Regardless please wear a helmet.

Cheers

Belt install on most CVT transmissions reqires primary or engine pully to be removed or disassembled. 

Do you have pictures of this pulley system your description has me confused