To bore a stock carb or not?!

#1
I'm just learning about carbs and how to build up a motor. When should I consider getting my stock carb bored out?
Besides the air filter and exhaust, what supporting mods do I need?
How much performance is average on just boring the carb?
How much do most shops charge to bore a stock carb?
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#2
Boring a carb out??? Never heard of such a thing. Boring out a cylinder? Yes. Absolutely. All of my bikes except one has a bored cylinder.

But a carb? I don't think so. There are many things that can be done to a carb - change a main or idle jet.

A cylinder bore can set you back maybe $60-80 depending on the engine and what part of the country you are in.

Rick

2006 Honda Foreman - Green
1973 Honda ST90 - Mighty Green
1974 Honda CT90 - Shiny Orange
1975 Honda ST90 - Topaz Orange
1976 Honda CT90 - Mars Orange
 

rmm727

Active Member
#3
you can buy the flex hone to bore a carb for like $15. Or you can buy bored carbs depending on how big you want to go for $50-$100
 
#4
I just installed 140 e-tube and have a .36 main jet. Just looking into what I can do more to my stock carb. There is a local shop that I could have do the work. Just wanted advice before I make any decisions.
 
#7
A 22 mikuni will support a huge motor. You'll be fine with one of those. I doubt you'll ever build a motor too big for it. It does require you to buy an adapter (or make one), and I think they're really expensive for what they are. In my opinion, billet parts for the inside come first. Then go for an upgraded cam and valve train. You'll feel the biggest performance gains here. You can put a huge carb on a stock motor, but you'll still float your valves at 5500 RPMs. Building a motor is complicated. Some parts work well in one setup, but not as well in others. I'll suggest compiling a list of what you want. Remember, a race motor is great for racing, but not as great for just cruising. The black mamba jr. will produce a lot of power in the 2000-6000 rpm range (if I remember correctly). There are other cams that produce power from 4000 to 8000. Where will you be running the most? If you want to a of torque, and you're going to keep it under 6000 RPMs, the you won't need a 22 mikuni. If you're wanting to hit 8000 RPMs, go for the big carb and a black mamba (not the jr.) or a dyno CM cam. Without a plan, you end up buying parts that may not work with the next part you buy. Look at some of the build threads, and ask questions. Guys on here are happy to help. If you're close to Indy, jump on 70 and head east to the New Castle Motor Park some Saturday or Sunday. They do race clones there. It's mostly 2 stroke stuff, but there is a clone class. Comet Kart Sales also has guys that build motors. They may be able to guide you. If you're ever up by muncie, look me up. I'm not a builder, but I love to drink beer in the garage and play with motors.
 
#8
There is also the carb for the gx390, but that will also require a carb adapter. Your current throttle cable will work with it. The mikuni may require a different throttle cable because it hooks up differently. You may be able to use your current cable with a mikuni. Somebody will chime in on that. Going fast isn't cheap.
 
#9
I was thinking:
Black Mamba Jr cam(26lb springs)
Billet Flywheel
Billet rod
Remove governor and low oil sensor

I'm building it for short track/ street fun type of riding.
 
#11
The carb adapters are so long that I couldn't fit my filter on the filter adapter without hitting the frame. That's why I wanted to just improve my stock carb. Any ideas?
 
#12
There are several kart shops that do bore carbs. I have one from Dover Power. It's bored to .650 runs on gas and goes like heck. You can call and they will discuss with you what you want and make it just for you.
 
#13
I have bored the venturi on Tecumseh and Honda carburetors, sometimes they need a little more. There are a lot of people running carburetors that are way to much for their build also. The knowledge in these kind of things comes from years of trial and error and it is very hard to tell somebody what they need without seeing what they have. IMO of course.
 
#14
There are several kart shops that do bore carbs. I have one from Dover Power. It's bored to .650 runs on gas and goes like heck. You can call and they will discuss with you what you want and make it just for you.
So I could send mine in and they'll work on it?
 
#15
I have bored the venturi on Tecumseh and Honda carburetors, sometimes they need a little more. There are a lot of people running carburetors that are way to much for their build also. The knowledge in these kind of things comes from years of trial and error and it is very hard to tell somebody what they need without seeing what they have. IMO of course.
Yeah I've seen a few guys with carbs too big for their muscle cars because it's almost like over-compensating for the motor itself, yet with properly tuned and rejetted carb would work better for them. Which is kinda what I'm asking. I just want to make mine better.
 
#16
There are several kart shops that do bore carbs. I have one from Dover Power. It's bored to .650 runs on gas and goes like heck. You can call and they will discuss with you what you want and make it just for you.
^ This...stock appearing and killer power!


Sent from my Texas Instruments Speak and Spell...[emoji2]
 
#18
I also have that Dover "cheater carb". I have been really happy with it. I also called and talked with one of the guys at Dover, and he was awesome. I told him what I have, and he gave me his recommendations. I asked about the 390 carb, but he said it was way too much for my build. I can turn around 8000rpms with mine. That's pretty good for a motor that is designed to turn around 3500. I have way too much invested in mine, but I did mine in small increments. Like I said, get a plan, and stick with it. I think you'll be happy with a bored carb and the items on your list. Remember, stock bits will keep you from reaching your potential...especially the cam and valve train. That's where you'll see the biggest difference in performance with your setup.
 
#19
I also have that Dover "cheater carb". I have been really happy with it. I also called and talked with one of the guys at Dover, and he was awesome. I told him what I have, and he gave me his recommendations. I asked about the 390 carb, but he said it was way too much for my build. I can turn around 8000rpms with mine. That's pretty good for a motor that is designed to turn around 3500. I have way too much invested in mine, but I did mine in small increments. Like I said, get a plan, and stick with it. I think you'll be happy with a bored carb and the items on your list. Remember, stock bits will keep you from reaching your potential...especially the cam and valve train. That's where you'll see the biggest difference in performance with your setup.
Thanks for the advice. I'll have to contact them when I'm ready to spend more money. It's definitely addicting.
 
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