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Help me Reason Out My Next Step In The Carb Modification

  • Thread starter Thread starter Anonymous
  • Start date Start date
A

Anonymous

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THE NEW SET Of CARBS ARE 36mm COMPARED TO THE STOCK 34mm--I HAVE 150 MAINS IN MY STOCK CARBS WHICh WORK WELL WITH THE EXHAUST SETUP AND OVER BORE THAT I HAVE. NOW I WAS THINKING THAT I HAD TO GO TO A LARGER MAIN JET WITH THE NEW CARBS BECAUSE THEY WOULD RUN LEANER---BUT NOW I AM SEEING THAT A LARGER CARB ON THE SAME ENGINE WITH THE SAME 150 JETS MIGHT RUN RICHER BECAUSE THERE WOULD BE A BIT LESS VELOCITY PAST THE MAIN JET DUE TO THE LARGER DAMETER OF THE CARB---OK OK OK HELP ME CLEAR THIS ONE UP IN MY HEAD ((or any where else)) PLEASE.
ASUME THE RUNNING CONDITION IS FULL THROTTLE AND RPM'S UP WHERE THE CAMS ARE WORKING
 
Big Carbs

Big Carbs

Bigger carbs will tend to run leaner on the same setting. By enlarging the carbs, you slow down the air flow. Therefore, the jets have a weaker vacuum drawing fuel out of the bowls and into the motor. This will make them run lean, be harder to tune, and be more sensitive to jetting changes. It can also allow the engine to flow more air, but unless the rest of the engine has been flow optimized (Hi-flow exhaust, ported and flowed head, Hi-flow air filter, valve seat job) chances are you are making a lot more work for yourself without a being able to truly extract the potential of the bigger carbs. But you never know.
 
Re: Big Carbs

Re: Big Carbs

SamH said:
Bigger carbs will tend to run leaner on the same setting. By enlarging the carbs, you slow down the air flow. Therefore, the jets have a weaker vacuum drawing fuel out of the bowls and into the motor. This will make them run lean, be harder to tune, and be more sensitive to jetting changes. It can also allow the engine to flow more air, but unless the rest of the engine has been flow optimized (Hi-flow exhaust, ported and flowed head, Hi-flow air filter, valve seat job) chances are you are making a lot more work for yourself without a being able to truly extract the potential of the bigger carbs. But you never know.
Click to expand...

thanks for the reply sam--i have a star pro stock hedder and run a stock replacement K&n (no air filter box) now--i will install k&n pods when i put these 36mm carbs on--i didnt think i was going over board with the 2mm oversize carbs size since 36mm carbs are stock on 1150s and these carbs are off a stock 750 Suzuki kat-- the head work is way down the line and i will go to larger carbs again when i finally get the money for a properly modified head
 
I'll be following this thread, too, as while I try to resurrect my latest GS750 acquisition, I'll also be performance modifying it. I'm especially interested in jetting questions for the larger carbs. Here's what I've got in mind:

1. Larger carbs (34mm from an 1100 vs. 32mm stock on a 750) - Needed to buy something, since stock carbs are pretty frozen up. Need to figure out how to jet these.

2. K&N pods (what part number do you guys use, by the way?)

3. Overbore kit, if available

4. Perhaps a bit of head work.

5. 4-1 header.

6. Really fast paint!!!

Any other suggestions to make this resurrection process a bit smoother? Are there alternate cam setups that others might suggest, as well, or should I just stay with the stock cam? Probably need a stronger clutch, as well, I'm guessing.

Will probably take the better part of a year to get all this done, as this is just a side project. Cash will come from buying/fixing/selling all the cheap bikes that I come across (starting to be a really bad habit!).
 
Remember what sam said as far as jetting--you should start with your exhaust system before you do anything- without a true performance exhaust system your other work is a waste of time--you will be hearing the noise from the pods and swear that you are producing more HP--K&n adds are deceitfull as i see it--more air does not mean more power. as sam said truly the head work is next in line--but money doesnt always allow it--if you have a tscc 4valve engine then the minor changes will work ok-- as for the big bore kits--the word can be misused--a sensasble afordable over bore is is up to the service limit of your engine--3mm in most cases. Big bore kits require the splitting and resizing of the cases to accept the larger sleeves of the true big bore kit.
The turbocharger allows you to do lots of normal riding and yet have the reserve power of a highly modified engine--if you are buying and selling bikes why not just go for an 1100cc job or find an 1100 engine to install in your 750 frame--some of the guys have done it but i know nothing about the mod
 
R-Tru-D2, selecting cams depends on what you want out of your bike. The stock cams are great for streetability. If you want great stoplight to stoplight performance, go for something around 240 degrees of duration, if you want better quarter mile performance go for something closer to 260 degrees... Keep in mind, the longer duration will make it absolutely suck to "just ride". It'll also slow your stoplight to stoplight performance.
 
SLOWPOKE said:
YOUR FACE IS A LITTLE BLURRY
Click to expand...
Yours, however, is looking much better than before. Until now, I figured you were at least 70 years old with that previous pic!
 
k+n's

k+n's

SLOWPOKE said:
-K&n adds are deceitfull as i see it--more air does not mean more power.
Click to expand...
The stock airbox is a pretty good design, the reason people have such patchy experiences with k+n filters is that the CV carburettors need to drink air from a still air chamber to work correctly as designed, the small pods dont allow this properly, hence all the odd flat spots that appear. On slide carbs, I prefer alloy bellmouths with a flashback mesh to keep the bigger bits out the motor/stop small children being sucked in as you drive past.
The original deisgn is pretty good flow wise, having said that the original airbox is a royal pain in the arse for getting the carbs on and off when the rubbers go hard with age. Has to be the true reason to go to pod type filters. Im not sure if the rubbers are still availible, but in the past I bought new ones and it was a pleasure to take off the carburettors with them...
I hate carburettors 8O
 
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