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"WHAT SIZE" CARBS

  • Thread starter Thread starter tofast
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tofast

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Hello All I have a question and need some imput. Rebuilding my motor again 82 GS1100. I have put a 1260 kit with falicon crank, 1150 big end, HD case bolts, HD cylinder bolts, clutch basket rebuilt and the head has been ported, polished and a valve job. Need some info on what would be a good CARB size and cam size. I run a straight pipe also. Thanks for any info you can give me. I dont want to spend extra money on buying 2 or 3 different carbs to find the best performance.
 
Close, but the best is Mikuni RS38's, that eliminates the CV part altogether and gives you great response. The RS36's are a good choice too, probably better, unless you do a bunch of porting too. I have the 38s and love them.
 
But how should we choose carbs? I have had no luck trying to find suitable carbs for my bike. The stock ones, I am sure are ok. But I am curious as to what else is available. "blankblankblank form a blankblank" is a start, but knowing the specs of carburators is much more usefull. 38mm, 20mm, whatever isn't so helpfull.

Where can I find CFM ratings? Things like that are what I need. :-)
 
I have a book called "A Guide to Motorcycle Drag Racing" and in the book the author uses this formula to pick carbs.

Engine displacement divided by 35.48 equals the carb size in mm. Add 2mm more to the result for CV carbs.

In your case that looks like:

36mm for RS type carbs and 38mm CV type carbs.

I will be putting on a set of 36mm carbs off an 89 GSXR on my 821100e this spring. My bike is currently still an 1100 but will be an 1166 come 05/06. I bought these carbs on EBAY for about 140 dollars, new RS carbs are closer to 600 bucks or more.
 
Well that seems to be a little off.... That would say 17mm for CV carbs on my bike. Which is smaller than stock.

That math falls apart becuase flow goes up in a non linear fashion to the size of the opening. IIRC a hole twice as big in diameter flows sixteen times as much air.
 
If it's a drag only bike then trons are the way to go. 38's should be a good choice and as for cams 460's should make your ported head breath.
 
Nerobro said:
Well that seems to be a little off.... That would say 17mm for CV carbs on my bike. Which is smaller than stock.

That math falls apart becuase flow goes up in a non linear fashion to the size of the opening. IIRC a hole twice as big in diameter flows sixteen times as much air.
Click to expand...

All the examples in the bike were larger displacement bikes 1000 and greater. The book included examples of the same bike with different sized carbs and 1/4 mile times. The smaller carb made increased velocity improving performance over larger carbs on the same bike.
 
Bigger isn't always better. I would think 36 or 38 flatslides. I have both, but have never tried my 38's.
 
carbs

carbs

You have to choose your carbs for the intened purpose of the bike, 38 and even 40"s for all out drag racing if you have the mods to handle them, if your doing street drag racing as in light to light then a smaller carb say 34's would be best so that you have some thottle respone and it wont bog out on you at launch, the same for doing mountain road racing or the canyons you do not need a large carb with poor throttle response, the guy on the stock bike will eat you up in the turns, even if you catch up in the straight, like rosce says bigger ain't always better, you build your bike for the intened purpose and dont just start buying the biggest or hottest hop up part there is, and the badest engine in the world wont do crap if the rest of the bike isn't matched to take advanvage of the engines perfomance , so to say it simple there is no one answer, and the carb formula that was given here is for 1000cc's and up and then you have to add to the formula for the mods that are done
 
But that still doesn't answer the question. It's simple to choose carbs based on their cfm rating. I can, without having to buy three sets of carbs, choose the right carb for a smallblock with just a little math.

What "are" the cfm ratings for different bore motorcycle carburators?

Just as a note.. IIRC a 550 has 32mm carbs on it...
 
I might lean toward the 36 for street use. If you go too big you will kill throttle response. I have a friend that runs 9 teens with 38's on a 1428 drag motor.
34mm MIKUNI Carburetor 109.15 CFM
35mm MIKUNI Carburetor 114.70 CFM
36mm MIKUNI Carburetor 109.33 CFM
38mm MIKUNI Carburetor 129.50 CFM
 
rosco15 said:
I might lean toward the 36 for street use. If you go too big you will kill throttle response. I have a friend that runs 9 teens with 38's on a 1428 drag motor.
34mm MIKUNI Carburetor 109.15 CFM
35mm MIKUNI Carburetor 114.70 CFM
36mm MIKUNI Carburetor 109.33 CFM
38mm MIKUNI Carburetor 129.50 CFM
Click to expand...

Are those the RS specs?
 
Thanks so far for all your responces. To answer some questions. Im going to be riding most of the time on the street and every other weekend at the strip. Just trying to get the best all around performance. I want to be able to keep up with the newer bikes.
 
I just hunted around on the internet and found that. It didn't say.
 
I found that too. But given it doesn't say what model carb they are, or the inches of water tested with it's not all that usefull.
 
36 to 38mm flatslides...They have a choke and are easy to jet and tune. You can run them with your stock throttle cable...I did mine for years w/o any problems.
 
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