Does size really matter....Carbs that is?

[speedy]

Just a quick one regarding the differences various carb sizes make. Over the years on different performance tunes/kits etc, we have used various carbs in open mouth set up from say 28mm to 38mm, from Amal , Dellorto ,Keihin ,Mikuni etc etc. Bigger the better was the opinion of some as I remember Dj 240 Kawasaki stage 6 motors with 36mm Amal's and tuned ts1's with 38mm Dell orto's etc. Now with such things as the super Monza being designed to run a 30mm vhsh flatslide Delly, the big block GT running a 30mm phbh etc, how much bhp and or speed is reckoned to be lost by using a smaller carb ,if any? I have changed from my beloved Amal 34mm on my standard set up TS1 to a 30mm Flatslide vhsh Delly on the claims of them being more economical and perhaps more responsive low down,but allegedly at the cost of bhp and or mph. What is the thinking behind this, or is it just a bit of tosh? cheers,Speedy.

[goldeneye]

my 2 pennorth". ive just changed from a 30mm delly to a 28 KOSO "D" slide, and its better all round , more responsive and better on fuel, and a bit quicker as well. someone who gets on here changed to a 28mm delly on his TS1 for the C2C at the weekend, and saved on fuel, and didn't think it was any slower than his 34mm carb...he is a tight arse mind, so probably just talked himself into thinking it was better

[tonydevon]

I changed carb on 198 mugello from 28 dellorto phbh to a 26, gained power and torque

[bristolmod]

"Gas Velocity"............

Smaller carbs are generally better at low PRM but run out of breath at high RPM
Larger carbs are worse at low RPM but perform better at high RPM as they can gulp more air.

Try blowing a match out with your mouth wide open- hard isn't it?

Now try with your lips more together- easier!

Very simplistic view of mine but has some truth I think.

Chris

[soosh]

My TS runs a 30mm now and goes really well but I will still say the old 34 Amal gave it better mid to top end power.

[sean brady scooters]

harking back in time to the 80,s ,the carb of choice was the 34mm amal ..as it was used on the track and by AF for their scooters ,the TS1 was developed using this and the old fresco pipes as i recall ,but now things have moved on a bit what with the use of dynos and extensive testing by tuners and various pipe designs ...
and also you have to be aware that the ts1 is such a good versatile kit even now ,and will
still deliver great results in either STD /touring tune /race spec ..each spec requiring a different carb size to suit .
pipe design now has also helped things on a great deal since the fresco era .providing more max power along with a greater spread of power and torque .

[Special X]

I've just changed from a 26mm PHBH to 30mm PHBH on my tuned 230cc iron barrel which is on a 42mm clubman at the moment. It's much faster on the 30 From about 3,000 rpm up it's got much more power, doesn't lose anything at the bottom end either. However I don't think going larger than 30mm would be of any benefit.
I've had great results on 186 mugellos with the 26 PHBH but I reckon the larger port area and the extra 45cc's made the 26 too small.

[speedy]

harking back in time to the 80,s ,the carb of choice was the 34mm amal ..as it was used on the track and by AF for their scooters ,the TS1 was developed using this and the old fresco pipes as i recall ,but now things have moved on a bit what with the use of dynos and extensive testing by tuners and various pipe designs ...
and also you have to be aware that the ts1 is such a good versatile kit even now ,and will
still deliver great results in either STD /touring tune /race spec ..each spec requiring a different carb size to suit .
pipe design now has also helped things on a great deal since the fresco era .providing more max power along with a greater spread of power and torque .

With this in mind, just out of curiosity, if you had two identical motors,say standard TS1, same pipe on each,gearing,electronics etc, but a 30mm on on and a 35 mm on the other. Would you expect to see any power or top speed between the two on the dyno ,or would they be so very similar. Thanks everyone for your input. Just to mention, I do run a Fresco on mine,proper olde worlde ,but I like it.cheers,Speedy.

[YAMLAM]

i seem to remember a post on LCGB many moons ago by ,i think David Blythe, who ran a TS1 225 with a TMX35 and then tried a 26mm Delly, obviously with the smaller carb acceleration was poor compared to The tmx but top speed was only down very slightly.
tried searching for it but couldn`t find it. perhaps it was a drug educed dream.

[speedy]

i seem to remember a post on LCGB many moons ago by ,i think David Blythe, who ran a TS1 225 with a TMX35 and then tried a 26mm Delly, obviously with the smaller carb acceleration was poor compared to The tmx but top speed was only down very slightly.
tried searching for it but couldn`t find it. perhaps it was a drug educed dream.

Cheers mi duck for that. I have always been of the old thought train that big kit/tune, needs big carb for air and fuel supply to achieve high power. Sean made some interesting reading about changes and development in pipes. As I said, I used to run a 34mm Amal on me standard TS1 and my previous Webster tuned Yam TS1 and I loved that carb.....I love Amals. I only changed as I started getting bad fuel figures which was said to be down to worn parts in the carb, but with hindsight, this may have well been down to an electrical issue. I expected when I went down the 30mm vhsa route that I would lose a fair bit of speed, but it doesn't seem to have. Just wondered what the real figures would relate like on a dyno.Thanks again,Speedy.