Alternative Carbs...

[adam]

Originally posted by clarkie49
thats some pretty colored carbs you got there

Thats' some frickin' expensive looking carbs as well !!!

what exactly is 'PSI big air carbs' ???

ok PSI stands for pounds per sqr inch & big means 'not small' & air is what carbs suck in,

but what does it all mean ?? !!!!!

[wsmc667]

Originally posted by clarkie49
wow, my cup legal bike made 66hp on pump at willow back in 2000

i still dont get why people arent making 70hp with a little more compression (0.6mm squish) and good fuel.

i might have to tear apart our stock shop RS250

Yeah, Louie has had his dyno "adjusted" twice since then, too.

[Micah / AF1 Racing]

PSI Engineering is the name of the company that makes the carbs in the pic. They are also the actual makers of the 316cc kits that so many of you are fascinated with.

The carbs were $1,600 including the manifolds....I have no idea why they are so expensive but they are anodized gold!

[clarkie49]

sorry chris but it wasnt on Louie's dyno

so are you in the 27's at willow yet?

[Kieran]

What carbs do the TZ250 yamaha's use? I think they are a TM38SS or something. Would be worth looking into. And fairly available.

Cheers

[bjoern]

there are some other options asvell
this is the dellorto carb 1500 gbp + vat 39mm

[bjoern]

and the newest keihin

found this on : sudco.com
dellorto.co.uk
the unproven carbs micah has: psiperformance.com

I`m looking forward to the dyno figures when micah test those bigair carbs.
and you can start putting in the overtime now because these carbs dont come at a discount
the dellorto carbs are a spin of from GP and they look very similar to the carbs aprilia use on the RS250. I think someone posted a pic of the dellort carb here some time ago.....or go to europark.com

regards
bjoern

[keean]

If you read from the beginning of the topic, you'll see it started with the suggestion of fitting a Keihin PWM38, which I think is one of the carbs you were refering to?

[Micah / AF1 Racing]

I personally would not go bigger than 38mm. 38mm carbs are capable of supporting over 90bhp on a dynojet from a 250cc 2-stroke twin cylinder motor. Bigger than 38mm will just make jetting more sensitive than it needs to be.

I really like the Kehin carbs....really like them....The needles in the Kehins are very good out of the box and a single clip position change makes a lot of difference in the numbers recorded by the data aq system from Digatron....We set up our race carbs to be rich on the needles and then to lean out on the main jets. This allows the piston to get extra cooling under part throttles and then really scream on the main without getting too hot on the straights. I also set up the pilot and idle circuits to be correct when the bike is on the pipe...not when it is idling in the pits...try this, it works. This little peice of advice was given to us by our oil sponsor (Dumonde Tech) and it is golden...

[wsmc667]

Originally posted by clarkie49
so are you in the 27's at willow yet?

Never got under 1:31. I keep the wheels too much in line to go faster. I know what it takes to go faster, just don't have the balls to use slipping front wheel as brake into all the turns and leave right control lever hanging in breeze. Kinda decided to take break this year; got tired of hemmoraging money.

[VinCBR900]

WHat was the concesnsus on this?

Did the bigger carbs make any imporvement or just more sensitive to jetting?

Cheers, Vincent

[Micah / AF1 Racing]

A 38mm carb set will both be more tempermental to jetting/atmospheric changes and be capable of making more power when on the pipes.

We will be using my pretty gold carbs soon so we shall see what gaines are in larger bore carbs.

[foxster]

So Micah, did you know that the 500cc GP bikes used 28mm carbs? I found that to be incredible but considering the rpm they run at and the throttle response they want, I can believe it. On one of my 50cc scoots, I can't use a 17mm carb because it creates too much velocity and the crankcase "packs" with air and the engine is hard to tune, but I put the 21mm carb on and it runs fine. Slower intake from the bigger bore carb. It does have a lot to do with the small port area of the 50cc cylinder as well. The pipe also plays a major role in the choking of the engine with the smaller carb. I have 2 scooters set up the same but the difference is the cylinder, everything else is exactly the same. And this is the only conclusion I could find. The difference in how the engine ran was the carb size.

D

[Kieran]

The real question is, what size is right for the Aprilia RS?
Its got 34mm round throat carbs. Better low down.
If you put bigger carbs on, it improves top end power at the expense of torque spread and ease of tuning.
This, of course, is partially dependant on what state of tune the engine's in, pipes, etc.

How would the RS go if you had, say, a 34mm D-throat, or a 36mm D-throat.
Same lowdown, round part of throat. And massive area at WOT, as the slide reaches the flat top.

Next questions:
1) What are the RS carbs made of
2) How receptive is it to modding like D-throat -so it looks like NSR carb down the bore

[VinCBR900]

Frank Wrathal in England does the D mod on the carbs for his 300cc kit. I think It is also taper bored by a few degrees to try and promote axtra gas speed too. The 'cone' is offset so it doesnt machine through the floor of the carbn into the jetting galleys.

Cheers, Vincent