Big cheap carbs

[JOOLZ]

I was looking at carbs wondering if I should change my 40mm Amal for something bigger. I have read a few reports of people looking for performance carbs for their big singles, there has been mention of HSR's in 42 46 and 48mm range as well as the bigger lectron carbs up to 52mm ! and harley performance carbs of various sizes.
The trouble is they are hideously expensive and rarely come up second hand. I discovered an alternitive, Honda VTR1000 carbs 48mm and you get a carb and one spare for under £100
I may very well swap to a VTR1000 carb when I fit my supercharger although I will be sorry to see my old Amal go

[Steve Lake]

what bike are you putting it on?

[JOOLZ]

Im putting it on my XBR500

[Steve Lake]

I think you'd need to do a bit more research on this, swept volume, diameter of intake port(s) etc, 'cos there is the danger of actually reducing the performance, as a larger carb will reduce the speed of the incoming air over the jets, reducing proper fuel mixture, and less mixture in the combustion chamber... I'm sure there are guys on here who can do the maths on this..

[JOOLZ]

Dont worry I have been building racing engines and custom bikes for 30+ years, I have a full dyno engine suite on my computer, a 48mm carb will still be a little small for my needs, but as I say If you are looking for a big carb on the cheap these are the ones to go for. A lot of the desert racers in America are currently using the HSR 42's and 46 to great effect for high speed. Even seen a 48 on a mini drag bike and that was only a 360cc side valve, went like stink and could out accelerate a modern 1000cc up to about 50mph

[Oldtimer]

So what was up with the 2" SUs? Plenty big enough for the Blown Vincent 'Super Nero' and that had 2 superchargers and 2 SUs!!!
They are easy to set up and Main jet changes are a doodle. Stick with your SU you know it makes sense.

[JOOLZ]

I did consider an S.U carb but I though it might be too bulky I dont have much room to work with

[onthecheap]

Why not try a Gardner carb ? they are not too bulky and have a remote float. Easy to set up too. Used one on my Manx for years. However as with all top kit they are not cheap.
A good source of info for choke sizes for all applications has to be Tuning for Speed by Phil Irving - my bible !

[JOOLZ]

Gardner carbs are great, but far too expensive, I only give myself £25 per week for the bike ( thats why I make so much myself)  Yes Phil Irvings tuning for speed is a great book

[johnr]

slide carb or cv?

[JOOLZ]

The vtr1000 carbs are cv's

[timbo]

Interesting thread, more education for me 

[welland99]

I often wonder what easy tuning mods have been proven to improve performance on an XBR500.  Lots of people post here and there on the internet about all sorts of mods, but there never seems to be much info about what difference they actually make. 

I've even read adverts about brand new flat slide carbs that will "dramatically" improve performance, but upon questioning the manufacturer, they cannot quantify their claims. 

If anybody can describe and quantify the improvement in changing carb (or anything else) on an XBR500, I'd like to hear from you. 

[SteveC#222]

I often wonder what easy tuning mods have been proven to improve performance on an XBR500.  Lots of people post here and there on the internet about all sorts of mods, but there never seems to be much info about what difference they actually make. 

I've even read adverts about brand new flat slide carbs that will "dramatically" improve performance, but upon questioning the manufacturer, they cannot quantify their claims. 

If anybody can describe and quantify the improvement in changing carb (or anything else) on an XBR500, I'd like to hear from you.

Like most tuning there isn't really one magic bullet. if you just fit ,say, a bigger carb, or a straight through exhaust or gas flowing it probably won't make that much difference on it's own, it's only when you put them all together as part of a package it really works.

For an XBR a 600cc convertion, gas flow, reworked cam and free flowing exhaust and  xl600 CDI would make life a lot more interesting.

This is a good guide . http://www.champsclock.com/gb500hu.htm

[welland99]

Like most tuning there isn't really one magic bullet. if you just fit ,say, a bigger carb, or a straight through exhaust or gas flowing it probably won't make that much difference on it's own, it's only when you put them all together as part of a package it really works.

For an XBR a 600cc convertion, gas flow, reworked cam and free flowing exhaust and  xl600 CDI would make life a lot more interesting.

This is a good guide . http://www.champsclock.com/gb500hu.htm

Thanks.... interesting....