Very limited knowledge here, but I would be looking closely at the carb. Especially since it has been sitting for a while. How does the jet needle(or is it needle jet) look? The one that has the holes in it that sits in the body of the carb. I've had those give me fits before on acceleration.

My newest KFX80 had me convinced it needed crank seals as it wouldn't pull vacuum through carb. I found the reeds were gummed nearly closed from years of sitting with fuel in it. Gotta love the ethanol fuel! I never understand why people don't run the fuel out of the carb when finished with a trail ride.

As recommended, I would compression check it, if nothing else than to rule it out.

I'm tuning in to see what the solution is...likely I will need it one day!

 

""Originally if I got it started and got moving I could drive it for hours.""
That's the key to why OPT and I know it's compression...OOOPS I meant we think it's compression...hehehe j/k
On the last page he explained how he did double check the pilot jet (the one with holes in it).

 

This is why you guys are the pros!

 

We'll see...Might not be compression.

 

Needs the comp test...need to eliminate that variable...although it starts so easily...almost like it's being choked...and dies when more throttle is given...still hung up on the a/f screw...yeah, need the comp test...

 

Don't think the owner mentioned exhaust flow or anyone asked. These little ones can get clogged up with oily residue over the years along with the exhaust port getting caked up with carbon restricting flow. Simple test to see if exhaust flow is good or not may come up with something. I've soaked exhaust systems in kerosene before along with taking a long bent punch and running up through the tail pipe through the baffle to open up some also. Could be another reason why it may just idle and not take throttle.Worth the owner taking a look at it.

 

I thought of that but with it running for hours, I didn't go there.

 

Sorry for the very delayed response

I took a new fuel line and went from the tank to the carb and it seemed to run fine. I had tested this theory before but didn't bypass everything. I ended up putting the new carb and choke back on with the old slide / needle currently. Replaced all of the fuel lines its now running.

Starts right away, drives good. We ran it for around 5 hours Saturday with 0 issues. I have a few other questions to see what others think:

1] I didn't do the compression test yet, I have the tester and can do this do you still think it might be an issue?
2] Right now I am .5 to .75 turns out on the a/f mixture screw, any more than that it loads up and still does not like to run (before replacing fuel lines I couldn't have it out at all). Could this be from pre-mixing gas / oil someone was telling me that causes them to idle a little hard.
3] It does have an occasional backfire around .5 to .75 throttle was going to look at adjusting the needle now and lean it out some?

Issues that have been fixed so far:
Dirty carb, bad choke and gummed up fuel lines

 

I think I made the suggestion of letting it idle and then pulling the plug...I'd like to see plug color. Compression test never hurts...if you have access to the tester it would be time well spent...

 

I attached 3 pictures of the spark plug, these pictures were taken after starting and letting it idle for 5 minutes. My son drives it every day though and has already ran about 10 gallons of gas through this ATV before I took these pictures.

I feel like the throttle is a bit on the touchy side, seems like it just wants to fly at times when just barley on the throttle.

All in all, with a new carb and fuel lines seems to be running great, starts easily and has never died. The A/F screw on the carb is still not in its factory spot I believe its 1 turn out, anymore and it would run for a while then die.

I have not done the compression test yet. We live in Nebraska and its going to be getting cold very soon here so I wanted to let him ride it and enjoy it while he can with the nice weather.