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Thumpstar 125 big bore

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Hey All, 

 

I recently bought a used Thumpstar 125. Seems like a decent chassis for the price of the bike but the engine seems to be a little low on power. Is there any recommended big bore kits for these bikes or other performance mods. 

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10 hours ago, Joel Bennett said:

Hey All, 

 

I recently bought a used Thumpstar 125. Seems like a decent chassis for the price of the bike but the engine seems to be a little low on power. Is there any recommended big bore kits for these bikes or other performance mods. 

China Land Pit bikes:

The more power they make the quicker they brake. Cheap, unreliable, disposable, junk. 

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9 minutes ago, adnohguy said:

China Land Pit bikes:

The more power they make the quicker they brake. Cheap, unreliable, disposable, junk. 

Thanks for the post but it didn’t help me whatsoever. Why do people always feel the need to flame a post? If you can’t answer the question just move along... 

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24 minutes ago, Joel Bennett said:

Thanks for the post but it didn’t help me whatsoever. Why do people always feel the need to flame a post? If you can’t answer the question just move along... 

Fair warning is all, been there done that. 

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1 minute ago, adnohguy said:

Fair warning is all, been there done that. 

Appreciate that but I have 2 ttr110’s and it looks like the chassis on the thump is much nicer than the ttr. That’s hard for me to say as I love yamahas. But anyway,  I figured I’d try the thump and see if I can build the engine a bit. 

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You can add a big bore kit but dont go over a 57mm big bore kit. you will most likely need heavier clutch springs to avoid slippage. You wont have to bore the case or anything. Most likely need to go up 2 sizes in main jet size and 1-2 sizes in pilot as well. With the big bore kit it would be a good idea to port the stock head while putting the big bore kit. Porting and match intake size to the head port to make the air flow better and polish if possible to get the most out of the motor. Carb upgrade would also increase power(26mm carb ideal) to get a decent power band. Just what i would do if i was in your shoes

Edited by Randy K

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9 minutes ago, Randy K said:

You can add a big bore kit but dont go over a 57mm big bore kit. you will most likely need heavier clutch springs to avoid slippage. You wont have to bore the case or anything. Most likely need to go up 2 sizes in main jet size and 1-2 sizes in pilot as well. With the big bore kit it would be a good idea to port the stock head while putting the big bore kit. Porting and match intake size to the head port to make the air flow better and polish if possible to get the most out of the motor. Carb upgrade would also increase power(26mm carb ideal) to get a decent power band. Just what i would do if i was in your shoes

Polish what again? 

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1 minute ago, adnohguy said:

Polish what again? 

Polish intake tube and polish the intake port of the head... Still waiting on my coffee to kick in

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Thanks Randy. Is there a specific big bore kit out there that fits these bikes? I can’t find any that specifically list the thumps. 

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7 minutes ago, Randy K said:

Polish intake tube and polish the intake port of the head... Still waiting on my coffee to kick in

Not the exhaust port then? 

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3 minutes ago, Joel Bennett said:

Thanks Randy. Is there a specific big bore kit out there that fits these bikes? I can’t find any that specifically list the thumps. 

Mainly all horizontal motors that are from china have the same head stud pattern and spacing so if you want one i would recommend a kit from tboltusa as they have a decent selection of parts. You can contact them and they could recommend a cylinder jug and piston that would work with little to no problems

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6 minutes ago, adnohguy said:

Not the exhaust port then? 

You could port the exhaust port but i have never polished the exhaust port personally so i cant personally recommend it as i have no experience in that.

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Polishing a port other than the exhaust port is a great way to limit port flow and slow things down....

You should read up on how airflow works a bit before dispensing such "knowledge"

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9 hours ago, mixxer said:

Polishing a port other than the exhaust port is a great way to limit port flow and slow things down....

You should read up on how airflow works a bit before dispensing such "knowledge"

Maybe someone with appropriate knowledge should help the man instead of being rude and not helping the man who wants help in the first place. Quite uncivilized

Edited by Randy K
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2 hours ago, Randy K said:

Maybe someone with appropriate knowledge should help the man instead of being rude and not helping the man who wants help in the first place. Quite uncivilized

Wrong...

I did help...

I'm protecting him from someone as rude as yourself... Who is not helping at all by dispensing misinformation and passing it off as genuine... 

You can't "know" what you said was correct because it is completely wrong, yet in an uncivilized manner you took it on yourself to not be quiet about things you don't have a clue about, you mislead people by not being quiet about things you are clueless about...

Now... As a public service, I actually do help a lot of people out with excellent and detailed information...

Randy K... If you would like to light a few candles in your fog on the topic of port flow... I suggest you search for the topic "porting, the final limiter to all components" in the DRZ400 section on TT... The engine is different, but the principles are universal...

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7 hours ago, mixxer said:

Wrong...

I did help...

I'm protecting him from someone as rude as yourself... Who is not helping at all by dispensing misinformation and passing it off as genuine... 

You can't "know" what you said was correct because it is completely wrong, yet in an uncivilized manner you took it on yourself to not be quiet about things you don't have a clue about, you mislead people by not being quiet about things you are clueless about...

Now... As a public service, I actually do help a lot of people out with excellent and detailed information...

Randy K... If you would like to light a few candles in your fog on the topic of port flow... I suggest you search for the topic "porting, the final limiter to all components" in the DRZ400 section on TT... The engine is different, but the principles are universal...

Seems to me you dont understand how these china pitbikes are set up from factory and the inconsistency of the intake and the intake port sizing alo ng with the poor finish in both limiting flow. You act like your all knowing but in the end you own incompetence makes you look bad in public view

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Randy, you never grow tired of being wrong.... Good for you feeling free to be who you are!!

First off... A rough surface finish breaks the boundary layer adhesion and always allows more flow... I thought almost everyone knew that by now.... You can polish an exhaust port to make clean up easier the next time, but it's only ok because the exhaust port will carbon up to a matte finish a short time after running....

You are obviously connected to the internet , and thus the collective knowledge of all mankind is at your fingertips... I suggest you take advantage of it and explore the rewarding activity of quest for enlightenment.... 

Be free Randy... Don't be scared... There is a whole world waiting for you to discover!!🤘

Edited by mixxer
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41 minutes ago, Randy K said:

Seems to me you dont understand how these china pitbikes are set up from factory and the inconsistency of the intake and the intake port sizing alo ng with the poor finish in both limiting flow. You act like your all knowing but in the end you own incompetence makes you look bad in public view

You pass up an excellent opportunity to expand you horizons and learn to apply what you learned, but you just shrug you shoulders and not even try it for your self or at the least, check it out to see if it’s Viable or Fake News. .....Sad 

And just because your all enamored with China Land Junk (Cheap, low cost) engines does not mean learning something new is any less viable, but as you will learn, that no matter what you do to China Land Junk, disposable engines, while the may or may not seem to run better after your done modifying them, they just expire sooner rather than later, and it was all for nothing unless you sell it before it destroys it self.  
Every one knows about how they are miss matched and simply thrown together at the China land factory, and like me, most all  already know that.  Been there and done that.

Several years ago I purchased  a “Name Brand” China land 4spd hand clutch 125 and then a new 140 for my 10 year old son and installed them, one at at a time of course, in his xr70 because I wanted him to learn how to use a hand clutch and have more power,  they both broke the Rt center case from broken kick start gears and dumped all engine oil out on the ground. Neither engine was over a year old. Good luck sir....👍🏻

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4 hours ago, adnohguy said:

You pass up an excellent opportunity to expand you horizons and learn to apply what you learned, but you just shrug you shoulders and not even try it for your self or at the least, check it out to see if it’s Viable or Fake News. .....Sad 

And just because your all enamored with China Land Junk (Cheap, low cost) engines does not mean learning something new is any less viable, but as you will learn, that no matter what you do to China Land Junk, disposable engines, while the may or may not seem to run better after your done modifying them, they just expire sooner rather than later, and it was all for nothing unless you sell it before it destroys it self.  
Every one knows about how they are miss matched and simply thrown together at the China land factory, and like me, most all  already know that.  Been there and done that.

Several years ago I purchased  a “Name Brand” China land 4spd hand clutch 125 and then a new 140 for my 10 year old son and installed them, one at at a time of course, in his xr70 because I wanted him to learn how to use a hand clutch and have more power,  they both broke the Rt center case from broken kick start gears and dumped all engine oil out on the ground. Neither engine was over a year old. Good luck sir....👍🏻

broken right side case is generally from kicking the bike over and have kickback. kickback is caused from not getting through the power stroke completely causing recoil and that is how you break the cases. i have a 2013 ssr 160 tr and never broke the case so im thinking it was user error. common on these bike cause people dont know how to properly get on the compression stroke. and to be real with you... you dont need to give the original poster a rude post on this thread, he came for help, not to have you come in and make him feal like he bought a bad bike. with kids i would of thought your mom would of told you to not say anything at all if your going to be negative.poor manners and trolling on the internet... seems your parents didnt raise you right

Edited by Randy K
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On 1/12/2021 at 8:10 AM, Joel Bennett said:

Thanks Randy. Is there a specific big bore kit out there that fits these bikes? I can’t find any that specifically list the thumps. 

if you would recommend you contact tboltusa via email or there phone on there website and they can recommend a piston and cylinder jug for your motor to get more power. dont let these trolls discern you from doing what you originally intended, there just hear to troll and be rude without giving any help. hope you have fun on that thumpstar bud

Edited by Randy K
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