Cant Get ATV to idle

[Drew7a]

I am struggling get this ATV to idle it was left with gas that turned sour.

I drained the tank, cleaned the carb (Ultrasonically) and sprayed carb cleaner through all the Orrofices), set the float to factory specs, check timing and checked valves.

It start right up with choke, but when you disengaged the choke, it start randomly spitting through the carb, then the idle tries to surge then it stops running. If you keep the idle high enough it wont spit. But I can not get it to idle low enough without it stalling.

This is generally a sign of plugged pilot jet, so I tried cleaning everything a second time to make sure. I also checked the regulator while running and it it showing 14+ volts.


Anyone have other thoughts?

 

[SubieRubyRoo]

Berryman’s B-12, unless you’re within driving distance of HPL to pick up their fuel system cleaner.

David said they’ve dumped it in the tank of OPEs & generators that wouldn’t stay running, give it a couple pulls, let it sit for 30 mins, then it will start right up. I haven’t had anything that bad, but have no data to dispute it, either.

 

[ripcord]

Could there still be some water in the gas? Motorcycle tanks are notoriously hard to get all the fuel out of when draining and water will puddle at the bottom so can be hard to remove.

 

[Big E]

Vacuum leak between carb and engine?

 

[Randol]

This

The pilot is the 1st to plug because of the very small orifice. You can run a single strand of multi strand copper wire through it. You don't want to enlarge the hole so avoid anything harder than brass. I have been surprised how little debris is needed to affect the idle performance. You didn't mention where your fuel or air screw is set at.
I almost gave up on my Yamaha pressure washer carb, wouldn't run right under load, I finally succumbed to running some copper wire through the main jet, even though I could see light through it. Fixed. If everything checks out, you may need a new pilot jet, needle seat? Is this a CV carb with a slide diaphragm? Check it.

 

[burbguy82]

I had a simalr issue with my Honda 250 Recon. Cleaning checked cleaned checked and repeated. Hoses all good, filter replaced, everything. Ended up getting a new Honda OEM carb, and has worked ever since. The addition of Trufuel, has made all the difference.

Hondas are notorious for hard starting, no longer, 6+years now, and they are barely ridden.

 

[Cujet]

It is likely that one or more of the multiple passageways is still clogged. Often right by the throttle plate, there are 3 or 4 tiny holes in addition to the idle jet's discharge.

 

[ironman_gq]

I've had poor valve adjustment cause the same issue. Lash tends to tighten up on these with wear and I've seen them get tight enough to not full seal, also seen loose timing chains do the same.

 

[Atvguy]

I've had poor valve adjustment cause the same issue. Lash tends to tighten up on these with wear and I've seen them get tight enough to not full seal, also seen loose timing chains do the same.

Worn intake valve is what I was thinking as well. I've seen it many times. The only way to fix it is to cut a new seat then replace the valve. If a new valve is put back in the old seat it will wear back out again in a year.

Here's what it might look like:

You could keep backing the lash out periodically and keep riding for a while but eventually the valve will pop through the head.

Here you can see there is no angle at all:

 

[Atvguy]

The pilot is the 1st to plug because of the very small orifice. You can run a single strand of multi strand copper wire through it. You don't want to enlarge the hole so avoid anything harder than brass.

I used steel guitar string with lots of kinks to act as saw teeth and slide the pilot jet back n forth over those kinks dozens and dozens of times trying to enlarge the pilot jet hole, but it's a LOT harder than you think. You'd never be able to do it. But it's a good way to remove corrosion that solvents can't.

I bought some wire gauge drill bits to enlarge jet holes and even those struggle to cut the brass.