Miss/Sputter at Mid to High RPM

Kevin E · 08-14-2023, 07:09 PM

I'm trying to figure out where to go next on my son's Tao Tao 125 ATV. t has a Sputter or miss at the higher RPM range. It start easily and runs great at lower RPMs, but as soon as you go middle to full throttle is starts to skip and spitter. If you slow down, it goes back to running fine. I thought it was likely a gummed up high speed jet, and after seeing that I couldn't take the carburetor apart, I got a brand new one and replaced the whole thing along with a new air filter, fuel filter and spark plug. Nothing changed and it it doing the exact same thing. I'm thinking it is something in the ignition, but I'm not sure what to try or replace next. The parts are pretty cheap, so I'm not afraid to replace stuff, but any help in the right direction would be greatly appreciated. Thanks in advance for any help or advice you can offer.

TominMO · 08-14-2023, 08:19 PM

What brand spark plug? If you are cheaping out and getting a Chinese plug, replace it with an NGK.

Kevin E · 08-14-2023, 08:31 PM

It is an NGK plug.

Bruces · 08-14-2023, 10:13 PM

Sounds like shit fuel to me .Take a sample and stick it in your freezer to see how much water you have .

Kevin E · 08-15-2023, 01:49 PM

Quote:

Originally Posted by Bruces

Sounds like shit fuel to me .Take a sample and stick it in your freezer to see how much water you have .

I thought of that too, so when I changed the fuel filter I also flushed the tank and put in fresh (no ethanol) gas at the same time. I have just ordered a complete electrical package from Amazon which included new switch, CDI box, stator, coil, and anything else that might be crap on this thing. I know I didn't purchase a high quality machine, just hoping to make it run decent enough for my son to enjoy before getting him a bigger and BETTER machine once he is a few years older.

Kevin E · 08-30-2023, 12:44 PM

So... After changing the ENTIRE electrical system, carburator, fuel filter, flushing the tank, air filter, and new fuel, the thing still doesn't run any better. Would there be something internally that lets it run fine at idle and lower RPMs, but spit and sputter at full throttle/higher RPM?

dirtbkr188 · 08-30-2023, 03:50 PM

Have you tried any fine-tuning with the new carburetor that you installed? Made any air or fuel screw adjustments? Moved the jet needle clip down a notch or two? Try a size or two bigger on the main jet?

david3921 · 09-01-2023, 07:10 AM

If you haven't done so already, set your valve lash. They notoriously come tight when delivered.

08-14-2023, 07:09 PM	#1
Kevin E Join Date: Aug 2023 Posts: 4	Miss/Sputter at Mid to High RPM I'm trying to figure out where to go next on my son's Tao Tao 125 ATV. t has a Sputter or miss at the higher RPM range. It start easily and runs great at lower RPMs, but as soon as you go middle to full throttle is starts to skip and spitter. If you slow down, it goes back to running fine. I thought it was likely a gummed up high speed jet, and after seeing that I couldn't take the carburetor apart, I got a brand new one and replaced the whole thing along with a new air filter, fuel filter and spark plug. Nothing changed and it it doing the exact same thing. I'm thinking it is something in the ignition, but I'm not sure what to try or replace next. The parts are pretty cheap, so I'm not afraid to replace stuff, but any help in the right direction would be greatly appreciated. Thanks in advance for any help or advice you can offer.
	0

08-14-2023, 08:19 PM	#2
TominMO Join Date: Sep 2021 Location: De Soto, MO Posts: 1,868	What brand spark plug? If you are cheaping out and getting a Chinese plug, replace it with an NGK. __________________ 2021 Lifan Xpect--sold 2022 Lifan KPX 1972 Honda CT90--The Carrot 1969 Honda CT90--The Tomahto Cheesy is the WDK (workplace drama king). Now retired. Nope, back in the saddle. Climate: The Movie https://www.youtube.com/watch?v=A24fWmNA6lM How our government really works https://www.youtube.com/watch?v=QjadCd0VRBw Question all authority.....think for yourself
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09-01-2023, 07:10 AM	#8
david3921 Join Date: Feb 2009 Location: Michigan Posts: 1,030	If you haven't done so already, set your valve lash. They notoriously come tight when delivered. __________________ 2012 Kawasaki Versys 1984 Honda Magna V65 2016 Rhino 250 2016 Tao Tao 125D
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08-14-2023, 08:31 PM	#3
Kevin E Join Date: Aug 2023 Posts: 4	It is an NGK plug.
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08-14-2023, 10:13 PM	#4
Bruces Join Date: May 2018 Posts: 1,572	Sounds like shit fuel to me .Take a sample and stick it in your freezer to see how much water you have .
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08-30-2023, 12:44 PM	#6
Kevin E Join Date: Aug 2023 Posts: 4	So... After changing the ENTIRE electrical system, carburator, fuel filter, flushing the tank, air filter, and new fuel, the thing still doesn't run any better. Would there be something internally that lets it run fine at idle and lower RPMs, but spit and sputter at full throttle/higher RPM?
	0

08-30-2023, 03:50 PM	#7
dirtbkr188 Join Date: Aug 2009 Posts: 496	Have you tried any fine-tuning with the new carburetor that you installed? Made any air or fuel screw adjustments? Moved the jet needle clip down a notch or two? Try a size or two bigger on the main jet?
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