Big Carb = Big Speed ?

Ben /

Feb 17, 2009 03:16PM

Some people claim a bigger carb without a kit will increase your mph. Other people claim it's not worth installing unless you have a kit.

I am looking for personal experiences with slapping on a bigger carb with limited performance modifications.

By limited I mean performance exhaust, gearing (sprockets),

air filters, stuff like that.

I am more interested in the gain without a kit installed, so experiences related to kits aren't very important to me.

Here's the bike I am working on

2001 Tomos Targa ST

Stock 14.12 Dellorto Carb w/ performance air filter (upjetted)

Biturbo Exhaust

27 tooth front sprocket (soon)

Post with what your bike had on it and the mph gain you noticed

Re: Big Carb = Big Speed ?

Ben /

benshark OP

Feb 17, 2009 03:20PM

I wanted to mention that I am thinking about putting a 16.16 dellorto on my tomos. I think a phgb would be too big and a 15.15 would be alright but maybe not much of a change.

Re: Big Carb = Big Speed ?

justin turner /

onlythebest131

Feb 17, 2009 03:21PM

i had a magical maxi 1 speed back in the day that would do about 28mph.

Then i put a biturbo on with a high comp head and upjetted. It went 39gps confirmed.

Re: Big Carb = Big Speed ?

#CrazyWayne™ rocks. #CrazyWayne /

powerchair

Feb 17, 2009 03:22PM

Its like running with a ski boot on one foot and a running shoe on the other foot.

Fast Bat out

Re: Big Carb = Big Speed ?

Ben /

benshark OP

Feb 17, 2009 03:24PM

How about a carb cuper...what did you do with that?

Re: Big Carb = Big Speed ?

Eric P /

neutral4x4

Feb 17, 2009 04:12PM

Larger carbs... portmatching... porting... intakes... more porting... you need to increase overall flow, not just the carb.

Re: Big Carb = Big Speed ?

Joel Corvine /

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joelc

Feb 17, 2009 04:26PM

Understand that a larger carb will not do much unless the volume of air that passes through it is in balance with the intake and the intake on the cylinder.

if the intake on the cylinder is 16mm in size then going any higher than a 16mm carb would not be worth it. Find your bottlenecks, where the air flow can not be increased and try to remove them. That is why kits are popular you can take your intake up to a 24mm or higher depending on reeds or not.

Re: Big Carb = Big Speed ?

Andy /

akpasta

Feb 17, 2009 05:33PM

I had a stock 103 with an 8mm carb on it. it maxed out at 20mph and four-stroked the whole time. Added an SHA 15.15 + performance exhaust + lighten the clutch = speedo says 40mph :)

doesn't mean if I put a 21 phbg i'd go faster

Re: Big Carb = Big Speed ?

Jeremy /

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jeremyo

Feb 17, 2009 06:15PM

Remember that carbs are measured by diameter, but the key to carb is the size of the bore

The area for a 14.12 (which is really 12) is 113mm squared.

15.15 is 176mm squared.

16.16 is 201mm squared.

So a 15.15 is 50% bigger than you stock carb and 16.16 is 77% larger.

Re: Big Carb = Big Speed ?

nick /

wheliwalkr

Feb 18, 2009 10:02PM

ben shark give me your cylinder i make you go faster. or $100 kit is not that much more expensive than a carb. a kit with you stock carb will do you better than a bigger carb on you stock cylinder I know from experience my white bike only has a 14mm on it

Re: Big Carb = Big Speed ?

Charles Cole (OFMC) /

cappy

Feb 18, 2009 10:30PM

^^^ I agree. My good friend and tech guy for Toomey racing gets dyno'd 85 HP on a ported stock Banshee motor with stock 28mm carbs. He claims throttle response is WAY better than the bigger carbs that are available. Big carbs only give you a slight edge on top, while sacrificing the low end.

Re: Big Carb = Big Speed ?

Graham Motzing /

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grahammotzing

Feb 18, 2009 11:22PM

for this specific setup, which i guess is what you care about, a 14:14 stock will help you some, but going past that is probably going to be more of a headache than its worth. the stock tomos intake is pretty small, so if you want to go faster, you'll need to improve the whole flow of the intake system, do porting to make the cylinder flow more, or add a performance exhaust. if you plan on making it really 'super-stock' you can totally use the 16, and the PITA factor of making it idle and tuning it on a stock bike will make you really good at carbs. ha!

good news is a superstock tomos can easily do 40-45 real miles per hour.

MOPED ARMY

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