Lets talk carbs and carb mods

[subxero]

Ok tuners educate me.

Is there much of a point in doing carb mods say boring, or just going to a larger carb with out making changes else where?

would you see gains with a larger carb while using the stock intake cams, timing and valves?

Are you going to get any more air in with larger carbs or simply get about the same volume air in with different velocities with out making changes else where?

could you change the vacuum pressure to suck in more air? is that possible? is this a good idea? would this be difficult?

if you are going to use larger carbs what additional mods would you use to complement the larger carb for best gains?

Those are the questions I have for now...

[KrazyWalle]

Originally Posted by subxero

Ok tuners educate me.

Is there much of a point in doing carb mods say boring, or just going to a larger carb with out making changes else where?

I hand polished the intake side when I rejetted mine. Started with 800 grit all the way up to 2,000 then I finishes them with some crocus cloth. Polished with a microfiber cloth and some compound. Idk if it did anything but they sure looked shinny and smooth.. It took me a few hours as well...

[Racer x]

The stock carbs are very good. I made as much as 34 hp with them. I did not see a drastic change going to. 31mm carbs. I made many changes to the engine and timing changes compression and exhaust changes. The stock carbs never seemed to be a problem. Time consuming to re jet com paired to race carbs. But flow wise they are very good.

A bigger carb without a major increase in engine volumetric efficiency causes the air to slow down. It has been proven more air And fuel will enter a combustion if the air fuel mix has greater velocity. So larger carb on a stock engine will have a negative effect on performance.

[kdogg2077]

Didn't you say like 3 days ago you were done modding the Ninja for while?

[subxero]

^yes, but that doesn't mean I can't plan for the future

[bruce71198]

The factory carbs are a compromise of drivability,emmissions, fuel economy and performance. Thus they are not a great performance carb. They may be a good performance carb but you will never tune them to FCR standards. Keep in mind that Kawasaki has to entertain many when selling a bike not just the performance guys. They have to make it ridable for all levels of rider, make it get acceptable fuel economy and keep Uncle Sam happy for emmission purposes. I am confident that given the same bike I could tune it for more power output with a set of 31mm FCR carbs than with the stockers.

[TnNinjaGirl]

Polishing is pretty much the best thing you can do to stock carbs. Bigger sized carbs can be used but generally you have to fiddle around with the jetting (duh) and they don't really do a ton of good unless you have bigger valves, cam work, port and polish the motor, etc... I think the limiting factor on these motors is the motors not the carbs but now I'm rambling Ducati. Also... Look into car carbs. I know Weber made some sidedraught carbs that I have seen hooked up to motorcycles. I'm not sure if they did that for parts availability or what.

[mgentz]

Originally Posted by Racer x

The stock carbs are very good. I made as much as 34 hp with them. I did not see a drastic change going to. 31mm carbs. I made many changes to the engine and timing changes compression and exhaust changes. The stock carbs never seemed to be a problem. Time consuming to re jet com paired to race carbs. But flow wise they are very good.

A bigger carb without a major increase in engine volumetric efficiency causes the air to slow down. It has been proven more air And fuel will enter a combustion if the air fuel mix has greater velocity. So larger carb on a stock engine will have a negative effect on performance.

I have cr33's and I love them. But you also know what I did to my motor.

[subxero]

could you oval bore a stock carb? How would it work with the throttle valves (or whatever they are) on the exit side since they would still need to seal at idle so you couldn't bore to much off that part of the inner diameter. I guess you could cut new ones and put them in to fit the new inner diameter (hmmm)

I have never futzed with a vacuum carb much so it is kind of new to me. Dirtbike carbs with mechanical slides are so much more simple.

I have a spare carb laying around and I just want to play around with it and really want to try to oval bore it out. Should be interesting at least if I don't completely destroy the carb in the process.

[bruce71198]

Originally Posted by subxero

could you oval bore a stock carb? How would it work with the throttle valves (or whatever they are) on the exit side since they would still need to seal at idle so you couldn't bore to much off that part of the inner diameter. I guess you could cut new ones and put them in to fit the new inner diameter (hmmm)

I have never futzed with a vacuum carb much so it is kind of new to me. Dirtbike carbs with mechanical slides are so much more simple.

I have a spare carb laying around and I just want to play around with it and really want to try to oval bore it out. Should be interesting at least if I don't completely destroy the carb in the process.

Give it a try. The area where the vacuum slide operates is actually smaller than the bore where the throttle plate is. Boring the vacuum slide area to the throttle plate size may help. Or find some bigger plates and bore it to your spec theres plenty of material there.