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Discussion Starter #1
Ive spent quite a lot of time trying to figure out if anyone has attempted to install a larger TB butterfly into their stock TB and cant seem to find any information.

is this even possible? i want to attempt this. porting the TB isnt an issue for me, but I need to find some how to's on butterfly replacement.

idk if im just not searching the correct terms or what but i cant seem to find anything.

can anyone help a fellow grommer out??

i spoke with Monkey Father today and we have both came to the conclusion that my stock TB may be bottlenecking my set up.

even if i fail miserably, it wont cost me much but time. im trying to get to 26mm. right now im running the finbro head with matching 25mm inlet, koso 170cc bbk with cam, chimera intake, pro circuit exhaust, api tech efi. 1st-3rd gear is amazing, but im having issues with 4th gear and its my belief i may not be getting enough air
 

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If you've taken monkey fathers time getting that advice I think it would be the decent thing to do to buy his bigger throttle body kit. Otherwise you're looking at trying to bore a 24(?) hole out to 26, on a perfect centre without wrecking it. If you don't get it centred it won't seal when you close the throttle. Most people can't use a mill that accurately. Most people including me don't have access to a mill at all.
 

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Discussion Starter #4
damnit thats what i was affraid of, im trying to limit my spending at this point
 

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As someone said before me- it can be done. However I seriously doubt that it would worth the effort.
Depending on the size you'd want to end up one can buy either PCX 150 TB (26.4mm) or a cbr125 TB (31mm) from a salvaged bike. Pre 2015 PCX has single cable throttle, later ones double wired. I've seen healthy 31M CBR units on fleabay for less than 20GBP including the sensors and injector.
Heck that is what I call value for money.
 

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Ive spent quite a lot of time trying to figure out if anyone has attempted to install a larger TB butterfly into their stock TB and cant seem to find any information.

is this even possible? i want to attempt this. porting the TB isnt an issue for me, but I need to find some how to's on butterfly replacement.

idk if im just not searching the correct terms or what but i cant seem to find anything.

can anyone help a fellow grommer out??

i spoke with Monkey Father today and we have both came to the conclusion that my stock TB may be bottlenecking my set up.

even if i fail miserably, it wont cost me much but time. im trying to get to 26mm. right now im running the finbro head with matching 25mm inlet, koso 170cc bbk with cam, chimera intake, pro circuit exhaust, api tech efi. 1st-3rd gear is amazing, but im having issues with 4th gear and its my belief i may not be getting enough air
What motor are you using, stock OEM motor
BBK 183 finbro with the heads and Port/polish inlet pipe.

Since we do not know what engine and mod you have I'll take a stab at what you need.
Bigger port/polish inlet pipe with matching 27mm plastic spacer. The stock OEM throttle body works great with the bigger inlet pipe and bigger better F/I
PC-150 F/I or Finbro 6 hole type 2 F/I
full exhaust system and matching airbox mod or upgrade.
Good map if you are using a PCV-WB02 unit.
Good cam
 

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Discussion Starter #8
here shortly ill be running the full blown finbro 183cc bbk. i have his head with bigger valves etc, and his inlet bored out to 25mm. i have the koso cam but may be upgrading to the DCR, idk yet. Chimera intake. i do have dual crower dual valve springs as well. pro circuit full exhaust, and finbros api with his map. aem guage with wideband o2, opmid temp guage, ohlins suspension, most of the bike is now carbon fiber with protaper honda mini bars. so basically the only thing that is stock is the TB itself

i ended up seizing my 170cc bbk last night due to my own stupidity and frustrations, but thats another story for another time.

hard racing is sending me everything i need to have the full blown finbro bbk, i just placed the order today
 

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here shortly ill be running the full blown finbro 183cc bbk. i have his head with bigger valves etc, and his inlet bored out to 25mm. i have the koso cam but may be upgrading to the DCR, idk yet. Chimera intake. i do have dual crower dual valve springs as well. pro circuit full exhaust, and finbros api with his map. aem guage with wideband o2, opmid temp guage, ohlins suspension, most of the bike is now carbon fiber with protaper honda mini bars. so basically the only thing that is stock is the TB itself

i ended up seizing my 170cc bbk last night due to my own stupidity and frustrations, but thats another story for another time.

hard racing is sending me everything i need to have the full blown finbro bbk, i just placed the order today
How'd you seize up the motor? Did you have to cut valve reliefs in the piston to run the Finbro head with larger valves?
 

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What 170cc kit did you seize, by any chance a BrianS 170? If it is a BrianS 170 do you have his ported head with the duel Crower valve springs and valve stem caps? PM me if you do.
 

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Ive spent quite a lot of time trying to figure out if anyone has attempted to install a larger TB butterfly into their stock TB and cant seem to find any information.

is this even possible? i want to attempt this. porting the TB isnt an issue for me, but I need to find some how to's on butterfly replacement.

idk if im just not searching the correct terms or what but i cant seem to find anything.

can anyone help a fellow grommer out??

i spoke with Monkey Father today and we have both came to the conclusion that my stock TB may be bottlenecking my set up.

even if i fail miserably, it wont cost me much but time. im trying to get to 26mm. right now im running the finbro head with matching 25mm inlet, koso 170cc bbk with cam, chimera intake, pro circuit exhaust, api tech efi. 1st-3rd gear is amazing, but im having issues with 4th gear and its my belief i may not be getting enough air
What 170cc kit did you seize, by any chance a BrianS 170? If it is a BrianS 170 do you have his ported head with the duel Crower valve springs and valve stem caps? PM me if you do.
Sounds like he seized the Koso 170 piston and was running a Finbro head and Koso cam. Probably stock valve springs or whatever Finbro uses. Sounds like the top end parts are fine and he's just getting a new 183 piston/jug. How'd you hurt it Moto?
 

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Discussion Starter #12
its pretty easy to figure out the setup ive been running, ive stated it in many posts and i have like 30 posts total.

anyways. ive got the entire throttle body apart, a couple things that can be done to add more flow to the stock TB that would be super easy

first of all the finbro inlet MonkeyFather built for me doesnt exactly mate perfectly which would require very very light porting

the 2 screws holding the copper cylinder(butterfly) can be ground down flat on the back side of the screw to be flat with the butterfly strap while also changing to smaller screws that are flatter that dont have such a big round head for such a small screw. both of those are very min but will def add more flow, and wont take me but maybe an hour

theres also an adjustment screw on the back side on the outside of the TB that gives the butterfly a stopping position. which allows it to stop inside the TB at a slant downwards. i def dont want to mess with that as im sure that is factory tested to be at its optimal position, which stops the butterfly exactly perpendicular to the funnel.
 

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Discussion Starter #13
Sounds like he seized the Koso 170 piston and was running a Finbro head and Koso cam. Probably stock valve springs or whatever Finbro uses. Sounds like the top end parts are fine and he's just getting a new 183 piston/jug. How'd you hurt it Moto?
you are correct, except i had dual crower springs. basically i screwed up on the initial pistion ring install, the rings didnt fully seat and were seaping oil into the combustion chamber and i didnt notice, i figured the smoke was just due to the rich AFR. well i eventually just ran out of oil while running WOT one night and it made some funny noise.

it shut down, but i was close to home. pulled the top end and the wrist pin was locked in the rod, the skirts were ramming the cylinder, which was the noise. it only ran like that for maybe 8 seconds before. so there was no other damage. i just finished a complete tear down. i also have pics if anyone is interested

my new finbro cylinder, je piston, wrist pin will be here tomm and ill be back up and running THANKS to HARDRACING and their super fast service and high quality customer service!!
 
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