Frank Angerano

Sounds to me like a CV joint slipping.  Prob going to need an axle.  Not a huge deal to fix.  Make some tight U turns in both directions and see if you hear the clicking.   If so then its definitely an axle.  

So heres a pic of the lights.  Not the best pic but they are a round bulbs about 2" in diameter .  I put  three stringers up.  
I ordered some nice steaks 🥩 today from the butcher to stack up in the freezer. Various cuts and some sausage.   Yard is ready for some bbq and beer 🍺. 

Drilled into the carb or on the bottom side of the carburetor to expose the air/fuel screw? 
Or the actual inside of the bowl where the main jet is ? 
 

It's common to find the bottom of the carburetor drilled out where the air/fuel screw is. Certain states mandate that the screw be factory set and covered for emissions reasons.  

If you have a strong click from the starter when you press the start button the only thing that could be wrong would be the starter.   OR the engine is locked up! But since you said the engine runs makes me lean toward the starter.  
When you pull start the engine is it hard to pull start as if the decompression device is not working ? 
Pull the spark plug and try to crank the starter. Let me know what happens.  

Yes sir. Lots of pre start grease on all moving parts.  Cam, rockers etc.  Crank the engine with out the spark plug in  to pump oil to the the head for a few seconds prior to starting.
I'm sure  you know this but i wanted to put it out there. 

Yep a simple diff lube is fine. Your welcome, be sure to post some pics of the new machine!!

Ok. Just wanted to make sure. 
We have seen a few unhappy campers with blown head gaskets etc.  

Yep no problem, one thing i want to mention. The gaskets that you got, are they quality gaskets? I just want you to be aware that the cheaper brands will come back to bite you in the as*. 

That's great info. Now looking at the age of the engine I would set the valves at spec and a hair more due to wear. But run it first and listen for any tapping.
What do you think ? 

Absolutely, i have the white also. 
I put up a cool light stringer in the yard and it looks nice.  I will post a pic later. 

Yep prob wont work under a load. Feel the starter for any slight click when you press the start button. 
Im guessing its the starter.  

When you jump the solenoid is there a spark by any chance? 
Take a tester put the positive lead on the starter wire at the starter and the other on the negative terminal on the battery.  Press the start button and see if you hear the relay click and get a voltage reading on the tester.  If not jump the relay and see if you get a reading that way.   
 

I don't think its adjusted with feeler gauges.  

Ok good pics. I see now, the valve adjustment is done by the bolts on the aide of the head and that should be listed in the manual.  Have you located that by any chance ?

If that starter was bench tested and spun freely and not on the atv it's probably fine.  
Do this; tap on the starer with a rubber mallet while your trying to start it.  If it works then its the starter or brushes. If not then jump the wires (larger ones) on the solenoid with a screwdriver. If the starter cranks then the relay is most likely bad.   You know what wires I'm talking about on the relay yes ? 

I like the post caps, solar type and they snap right on. 
Stair risers i like both hard wired and solar.  The can go right on the side wall or a recessed type in the tread riser if the deck is built with a tread riser cover.  
 

Hey @Jeff Miller welcome to Quadcrazy. When you pulled the starter out did you happen to bench test it with a battery ? It could be as simple as starter brushes or just a bad starter.  Pull the starter, strap it down to a work bench so it does not jump and then test it with a battery.   

Did you jump the wires that plug into the sensor and if so did the fan come on ? 
Im assuming thats why you ordered a new sensor ?

Hey @Billy Aldrich welcome to Quadcrazy. So what's happening here ? Is the engine idling ok and not too high where it could just be an idle adjustment ? Thats a semi automatic, Just a foot lever shifter yes ? 
 

I would think the clutch has something to do with this problem where you may need to open the side cover and take a look to see if its jammed up or stuck in any way. 
I would also drain the oil and see how it looks as far as any metal parts/shavings from a blown gear etc. 

But before all that:    
Can you explain how you think you got screwed? Did you purchase it from someone that may not have been honest with the mechanical condition? 
And can you bring it back? 

What do you mean half throttle ? 
Pull the spark plug and see what color it is and put a new one in while ur at it. 
if its super black it's obviously running rich and it could be the rev limiter.   98 goes back a little ways so I'm not sure but look on the throttle control on the handlebars  and see if there are wires going into it. 

Sweet, did you get a good deal ? 

Welcome to Quadcrazy @Tyler Reed ! As @Ajmboy said you came to the right place! Any repair shop that recommends you need to swap out the engine based on your symptoms is a shop I would never return to my friend!  So what i would do is start With the basic testing first.  

Does this happen during all riding or in damp/wet conditions? 

Go get yourself a cheap compression test kit from Amazon or anyplace.  Take a compression reading while its ice cold and then a reading after it starts to act up.   Compare your readings and see whats what.   
Secondly I would locate the regulator/rectifier and see if its over heating after the atv acts up? It's cheap enough to replace if suspected.    
Im not sure if your machine is water cooled  but is the cooling fan coming on? Could be getting super hot and causing the problem. Don't trust temperature lights etc. Visual verification of the fan running is key. 

Next I would check your air box and make sure everything is ok inside, filter good, no overload of gas inside the box or water? 

Lastly is making sure your fuel is flowing properly to the engine weather it be some sh** at the bottom of the tank or maybe a condition where this happens when you get to a certain fuel level in the tank ? And we have been talking about vapor lock by maybe a bad gas cap? 
 

Start with this and see how you make out.  
 

Agreed 100%

No problem. Keep us posted and be sure to take and post progress photos.