Sputtering at High Speed, TBR7

Bamakojon · 04-19-2022, 12:34 PM

I have a Tao Tao TBR7 that I'd like a little help troubleshooting. It has a Mikuni VM26 carburetor and an aftermarket exhaust--other than that it's unmodified. It starts and idles great, but it has a problem with sputtering when holding high speed (45+ mph) when it gets hot. It also feels like it has a delay in throttle response at lower speed, especially when rolling on or off, like it's "catching up" suddenly to the new throttle position.

I bought it used with the aftermarket parts on it, so I figured that maybe it was running rich because the previous owner put an oversized main jet on it, but I pulled the carb and the main jet is a 110, which from what I've read shouldn't cause issues. I'm going to be replacing the air filter because it is filthy, so hopefully it breathes a little easier, but I don't think that's the root cause. I did change the spark plug from the stock chinese one to an NGK and it seemed to help, but the problem didn't fully go away.

**JerryHawk250** · 04-19-2022, 12:44 PM

A clean filter would help. Also make sure that the choke is completely off and not half choke. Have you checked the valves for proper gap? Tight valve lash will cause all kinds of issues.

Bamakojon · 04-19-2022, 06:14 PM

Looking forward to getting the new filter for sure. The choke is completely off, but I haven't checked the valve gap, so I guess I'll do that soon. I took it for a ride today after removing and reinstalling the carb and changing the oil and it seemed to run better. There was actually a fair bit of oil in the airbox, so I'm wondering if it was enough that some was getting into the intake and causing the issues.

Nospark · 04-20-2022, 05:44 PM

I suggest you look at the basics. Air, fuel and spark.
From the limited info you've provided, I would focus on air 1st.
Fresh oil is always good but, likely not the reason for any improvement in how the motor runs.
make sure the carb is clean and not restricted with dirt or oil. Then check for leaks at the base of the carb & around the intake. You may fand a bad gasket or cracked intake housing. Air leaks of this type make it impossible to dial the carb in. You can check for leaks at idle by spraying carb cleaner or brake cleaner around the base of carb and intake. If you observe any changes in RPM, and your confident it wasn't from over spray down the throat of the carb, you have a leak that needs to be addressed.

willardnigma · 04-21-2022, 04:33 AM

I agree to check the air filter and intake and the choke and check for air leaks first.

Could also be a jetting issue. You never know if he got the parts off a reputable dealer The default jetting for the main is 110 to 115 (115 for my engine and area) With some cheapo kits from knockoff sellers that 110 could be a 100 or even a 90.
That's without exhaust mods. Need to go bigger when you do most exhaust mods as it starts running lean with it has less restricted airflow.

But first you want to dial in the pilot jet (which operates under 25% throttle. The default in most aftermarket carbs is WAY too rich which could cause the problems at the low end you're describing.

And lastly, double check all gaskets. You never know what gasket he attempted to reuse when he shouldn't have. You'd be surprised how many problems something as simple as the exhaust gasket could cause.

TxTaoRider · 04-21-2022, 06:44 AM

A couple things to check. As mentioned earlier, the main jet... is it a mikuni, a kehin, or a knock off. The mik and kehs use a different numbering system. I use the mikuni.

Is your gearing still stock? If so they'll just run past the power peak fast at like 50mph... which brings the next question... did you confirm your speedometer accuracy? They are off some on a good one, off allot on a bad one. Confirm it with your phone.

Last, replace the spark plug, check the gap, the stock one is known for being weak.

Since your bike doesn't have a tach you can't really tell the rpm it's breaking up at.

Bamakojon · 04-21-2022, 01:45 PM

Thanks everyone for the replies! I have replaced the spark plug with an NGK and it did seem to help a bit.

Here's my to-do list:

- Get new air filter
- check for air leaks around carb
- get a mikuni jet kit (and mess with all that)
- check valve gap (cuz really who knows when that was last done)

I would like to re-gear at some point, but there are a few things that I'd like to do first. My brother has a Hawk that he re-geared and has absolutely loved it since doing it. I have also read that upgrading the intake does some pretty good things on these bikes. I don't know how true that is, but it's something I'm curious about.

Thumper · 04-21-2022, 02:53 PM

Yes... Opening up the intake and exhaust both help a lot, as long as you jet the carb (and shim the needle) to match the better flow. It really makes a big difference, from stock. Revs easier, seems more willing, adds a horsepower or two.

04-19-2022, 12:34 PM	#1
Bamakojon Join Date: Apr 2022 Location: Birmingham, AL Posts: 3	Sputtering at High Speed, TBR7 I have a Tao Tao TBR7 that I'd like a little help troubleshooting. It has a Mikuni VM26 carburetor and an aftermarket exhaust--other than that it's unmodified. It starts and idles great, but it has a problem with sputtering when holding high speed (45+ mph) when it gets hot. It also feels like it has a delay in throttle response at lower speed, especially when rolling on or off, like it's "catching up" suddenly to the new throttle position. I bought it used with the aftermarket parts on it, so I figured that maybe it was running rich because the previous owner put an oversized main jet on it, but I pulled the carb and the main jet is a 110, which from what I've read shouldn't cause issues. I'm going to be replacing the air filter because it is filthy, so hopefully it breathes a little easier, but I don't think that's the root cause. I did change the spark plug from the stock chinese one to an NGK and it seemed to help, but the problem didn't fully go away. __________________ "Stupid it isn't if work it does." - Yoda 2019 Tao Tao TBR7
	0

04-19-2022, 12:44 PM	#2
JerryHawk250 Moderator Join Date: Oct 2016 Location: Houma, La. Posts: 11,725	A clean filter would help. Also make sure that the choke is completely off and not half choke. Have you checked the valves for proper gap? Tight valve lash will cause all kinds of issues. __________________ 2024 Linhai 300 ATV 4x4 2023 Lifan Lycan 250 Chopper 2023 Venom Evader 2022 Lifan KPX250 2020 Kawasaki Vulcan S (Sold) 2004 Honda ST 1300 2016 Black Hawk 250 (sold) Keihin PE30 carb,125 main,38 slow.Pod filter,ported & decked head 10:1 CR,Direct Ignition Coil,15/40Sprockets,NGK DPR8EIX-9,De-Cat,Dual Oil Cooler,Digital Cluster 2016 Cazador180 XL 2014 Coolster150 JerryHawk250.com My YouTube Channel
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04-19-2022, 06:14 PM	#3
Bamakojon Join Date: Apr 2022 Location: Birmingham, AL Posts: 3	Looking forward to getting the new filter for sure. The choke is completely off, but I haven't checked the valve gap, so I guess I'll do that soon. I took it for a ride today after removing and reinstalling the carb and changing the oil and it seemed to run better. There was actually a fair bit of oil in the airbox, so I'm wondering if it was enough that some was getting into the intake and causing the issues. __________________ "Stupid it isn't if work it does." - Yoda 2019 Tao Tao TBR7
	0

04-20-2022, 05:44 PM	#4
Nospark Join Date: Jan 2022 Location: Milwaukee, WI Posts: 167	I suggest you look at the basics. Air, fuel and spark. From the limited info you've provided, I would focus on air 1st. Fresh oil is always good but, likely not the reason for any improvement in how the motor runs. make sure the carb is clean and not restricted with dirt or oil. Then check for leaks at the base of the carb & around the intake. You may fand a bad gasket or cracked intake housing. Air leaks of this type make it impossible to dial the carb in. You can check for leaks at idle by spraying carb cleaner or brake cleaner around the base of carb and intake. If you observe any changes in RPM, and your confident it wasn't from over spray down the throat of the carb, you have a leak that needs to be addressed. __________________ 2021 TBR7D 17 front, 42 rear PZ30 Clone Milwaukee, WI
	0

04-21-2022, 06:44 AM	#6
TxTaoRider Join Date: Oct 2020 Location: Flower Mound Texas Posts: 904	A couple things to check. As mentioned earlier, the main jet... is it a mikuni, a kehin, or a knock off. The mik and kehs use a different numbering system. I use the mikuni. Is your gearing still stock? If so they'll just run past the power peak fast at like 50mph... which brings the next question... did you confirm your speedometer accuracy? They are off some on a good one, off allot on a bad one. Confirm it with your phone. Last, replace the spark plug, check the gap, the stock one is known for being weak. Since your bike doesn't have a tach you can't really tell the rpm it's breaking up at. __________________ 2021 Tao Tbr7 - "Lucille" Mods so far- Brozz swingarm, 21" front rim (Bridgestone Tw302 rear/Dunlop D606 front tires), Digital gauge cluster, pz30b pumper carb, after market hand guards, aftermarket brake and clutch levers, round fold away mirrors, Fly handlebars shortened slightly, 13t front sprocket 2009 Q-link Legacy 250 1982 Suzuki GS1100ES - "Jolene"
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04-21-2022, 04:33 AM	#5
willardnigma Join Date: Apr 2020 Location: Ohio Posts: 52	I agree to check the air filter and intake and the choke and check for air leaks first. Could also be a jetting issue. You never know if he got the parts off a reputable dealer The default jetting for the main is 110 to 115 (115 for my engine and area) With some cheapo kits from knockoff sellers that 110 could be a 100 or even a 90. That's without exhaust mods. Need to go bigger when you do most exhaust mods as it starts running lean with it has less restricted airflow. But first you want to dial in the pilot jet (which operates under 25% throttle. The default in most aftermarket carbs is WAY too rich which could cause the problems at the low end you're describing. And lastly, double check all gaskets. You never know what gasket he attempted to reuse when he shouldn't have. You'd be surprised how many problems something as simple as the exhaust gasket could cause.
	0

04-21-2022, 01:45 PM	#7
Bamakojon Join Date: Apr 2022 Location: Birmingham, AL Posts: 3	Thanks everyone for the replies! I have replaced the spark plug with an NGK and it did seem to help a bit. Here's my to-do list: - Get new air filter - check for air leaks around carb - get a mikuni jet kit (and mess with all that) - check valve gap (cuz really who knows when that was last done) I would like to re-gear at some point, but there are a few things that I'd like to do first. My brother has a Hawk that he re-geared and has absolutely loved it since doing it. I have also read that upgrading the intake does some pretty good things on these bikes. I don't know how true that is, but it's something I'm curious about. __________________ "Stupid it isn't if work it does." - Yoda 2019 Tao Tao TBR7
	0

04-21-2022, 02:53 PM	#8
Thumper Join Date: Feb 2021 Location: Kansas City Posts: 2,770	Yes... Opening up the intake and exhaust both help a lot, as long as you jet the carb (and shim the needle) to match the better flow. It really makes a big difference, from stock. Revs easier, seems more willing, adds a horsepower or two.
	0