Changing carb size

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Jun 8, 2001
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#1
Hi there.

I own a 92 Yamaha WR200.
It comes stock with a Mikuni TM30SS and i have the jetting nailed down just nice. (30mm sized.)

However, in search of more power, does changing to a bigger size carb would "release more power" ??? I was told a 34/35mm size carb would release more power.

Question I have is... how does the carb size affects the power?
I understand that smaller carb would have better lower end and likewise for bigger sized carb and top end.

However, in the process of jetting for the bigger sized carb, ain't we just simply downsizing the main jet and sizing up on the pilot so that we'll achieve wat it used to be when we were using the smaller carb??? So won't we be back to square one??? :uh:
 
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#2
not really, because then why would companies put 36mm or 38mm carbs on bikes if they could just put a 30mm on? a 30mm carb can only flow so much, bore it out, or buy a bigger one and the max air/fuel flow through it will increase. You will have to change the jetting, becasue you have chainged how much restriction there is, same as drilling holes in your airbox
 

ACS

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#3
The WR200 does respond well to a bigger carb but there is a few problems. You need a YZ125 carb and reed block and you will run into problems with the airbox and filter. The stock filter is very small and we had no end of problems racing them for 3 hrs in dust. Skins worked well but we got really good at changing the filter. A YZ125 air box will fit with mods. From memory we used a 1991 YZ125 for the bits. In the end we gave up and went back to the stock carb and jetted the stock carb way up and modified the needle (We actually sanded down the needle using a power drill and file and grit paper. Lucky it worked right but the idea was to richen the needle from 1/4 up. It took a bit of time but with a micrometer and careful work we got there. Thing was the bike was a rocket after that.) usin a SPES pipe and FMF muffler it was faster than most 250's enduros. With the bigger carb the bike lost its electric smooth feeling and power hit harder.
 
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#4
The WR200 does respond well to a bigger carb but there is a few problems. You need a YZ125 carb and reed block and you will run into problems with the airbox and filter. The stock filter is very small and we had no end of problems racing them for 3 hrs in dust. Skins worked well but we got really good at changing the filter. A YZ125 air box will fit with mods. From memory we used a 1991 YZ125 for the bits. In the end we gave up and went back to the stock carb and jetted the stock carb way up and modified the needle (We actually sanded down the needle using a power drill and file and grit paper. Lucky it worked right but the idea was to richen the needle from 1/4 up. It took a bit of time but with a micrometer and careful work we got there. Thing was the bike was a rocket after that.) usin a SPES pipe and FMF muffler it was faster than most 250's enduros. With the bigger carb the bike lost its electric smooth feeling and power hit harder.
Hi there... what did you do to the connections of radiator hose and original carb when you replaced the carb???
 
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#5
You are responding to a 14 year old post so you might not get a quick response back.
 
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jaguar

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#6
well for stragglers I will put my 2 cents worth here. To me its all about the flow velocity in the carb. Enduro bikes are designed with smaller carbs and higher velocity, probably for better fuel atomization at mid range revs. Here is my page on the subject: www.dragonfly75.com/moto/carbsizing.html