Twin carbs on some big singles ..why?

[willywombat64]

Only recently became aware that some bikes like the Xt600 ran twin carbs . just wondered what was the reasoning behind this added complexity /cost/bulk when many big singles work fine on just one . Could someone explain in simple terms please .
thanks
Bill

[Joe Crow]

Hi Bill

I had an old XT500 (and my dad had an SR500) both of which ran just fine on traditional single 'slider' carbs, and I was surprised when the simply gorgeous SRX600 was released with twin carbs: one 'slider' plus one 'CV' vacuum carb.

I remember reading something about the different characteristics of the two types of carb balancing out engine response/performance from tickover through the midrange etc.?

Not a particularly scientific answer, but your post struck a chord...

Joe

p.s. another interesting point: my Enfield Bullet 500 carries an exact copy of the carb which I used to have on a TS250 Suzuki (Mikarb/Mikuni VM28 )

[Paul-S]

A mate has an XT600 and most of the time it runs on 1 carb unless he's on a pace and gassing it - he gets around 57-60 when easy riding but this can drop to 30 sih when he gasses it and the 2nd carb kicks in

[Kjell Lindberg]

There could be many reasosn as to why some singles have dual carbs.

One reason is space, one big carb would not fit, but two smaller ones will.


Another reason is that carbs usually loves high flowspeeds, and one big carb, will have to cope with low flow speed at low engine rpm.
(Since a big carb has a large diameter throat, the flow speed is lower in comparision to a small carb, given the same volyme of gas is passing through them both).
Using two carbs, configurated in that way as one carb is taking care of low engine rpm, and the other takes command at higher rpm could be another reason.

I will not enter the" minefield" of >should I exchange my dual set up for a single set up<, sufficient to say, a dual set up, is normally requiring more service and tuning to give their best, but when properly set up, they usually performes better in comparision to a single set up.
The same applies to cars, were doubble barrel webers/dellortos/solex usually performes much better than one huge single carb.
I know there were US cars that used to run on one huge single carb, but at least they had two or four barrels within that carb body, and many times the carb were set up to
open the secon barrel (or third + fourth barrles) on higher rpms, just to get rid of problems connected with large diameter chokes/barrels at lower engine speeds.

Today, fuelinjection has solved most of the problems connected to big singles and carburation.

[Royce Cochran]

Yup, had a '65 Pontiac GTO 389 cu.in. and a '68 Dodge Charger R/T 440 Magnum 375 hp. Big 4 barrel carbs. Lots of fun!!! Back then gas was cheep over here. Also had a '84 XL350 with dual carbs(a real pain to rejet for altitude) just figured it was Honda's typical over engineering.

[Rubberchicken]

Indeed as Kjell said, the CV carb is for regular low to midrange use and the other one is an accelerator.