Superbike carbs

[tcmoggy]

Anyone had any experience with super bike carbs on a 2ltr twin cam?

Good, bad or indifferent?

[Guy Croft]

YEUCH!

GC

[TomLouwrier]

hi,

There was a thread on this a couple of weeks ago with some sensible arguments. You may read that too.
viewtopic.php?f=4&t=2161

Bike carburettors are just that: carburettors. They come in sorts.
I've worked on bikes and I guess you mean the Constant Velocity type that usually come in two pairs off a Japanese straight 4.
They are what SU and Stromberg would have been, or should have been, if they had innovated more and earlier.

These carbs are highly developed, but with a number of things in mind that you find in bikes, not cars. Like gravity feed (tank over the engine) and leaning in corners. Usually they use two cables to open and shut the butterfly valve. They are tightly integrated with the engine they were meant for.

Apart from getting them mounted (fabrication of custom manifold, etc), main issue is setting them up: they are governed by a needle in a jet and a spring. It's pretty hard getting the right needle in the right jet and height. There is not much knowledge around on them either, so you're not 'popping down to the shop' to get the right parts. Parts that are always described as 'for a Kawazuki, year xxx model yyy' and that is about all you will know of it's characteristics.
I know of only 2 places in The Netherlands that do both cars and bikes, so they would have parts, knowledge and tools in one place to make it work. Bike-only shops do not have dynos to take cars.

I've seen some installations on cars that were executed quite nicely and worked well, but the same goes for DCOE's or DCNF's on a motorcycle.
It can be done.
They are not black art, nor a magic bullet. You won't double your power or do 100 MPG with them.
And they won't be cheaper than carbs that were designed to go on a car engine either.


Tom

[Guy Croft]

MODEL POST!

Thanks Tom

G

[James Bowen]

Hi,

As the author of the thread that Tom attached to his post. I would say that he has pretty much got it spot on. Certainly he has encompassed most of the difficulties, and expence that I came upon in my installation. That said, I am very happy with the way the car performs, and it is a huge improvement in virtually every respect over the DCNF carburettors I had fitted before.

The only gain over a more conventional set up may be the ability (depending on the individual engine and car design) to design a manifold that is freer breathing and / or has a better angle than already exists on the market. - Difficult!

On the subject of setting the carbs up, again Tom is spot on. There can only be a few places in the UK able to adjust the bike carbs on a rolling road, though the number of places able to properly set up and carry spares for any carburettor are probably to be counted on one hand.If I did the project again, I would spend more money and go with fuel injection.

Hopefully this isn't too negative. If you can slap on a set of bike carbs for half the cost of a set of second hand DCOE's then I'd say go for it. But I doubt they are any better......

thank you James

[tcmoggy]

The reason I asked is that the engine that I'm pulling out of the car at present has super bike carbs on it. The guy whom I got the car from said they were the "most responsive" carbs that he'd had on a twin cam.

The engine I've bought currently has twin 44IDF's on it and these can be supplied with the engine at a price (and as always, money is a wee bit tight) so therefore I was wondering if it's worth keeping the bike carbs (and they do sound good) in favour of the 44 IDF's.

When I get a little more time I'll have a thorough read of the thread / post in the link.

Thanks for your input guys.

Jeff :-)

[tcmoggy]

Finally got 5 mins without interruption and managed to read through the thread in the link.
As Tom said, not a lot in it. I'm probably going to run the bike carbs to start with as I already have them and they are set up to run on a 2 ltr. I will see how I get on, and if needed buy the 44's and manifold.

Once again thanks to everyone for their input and solid data, as written in the thread there's nothing worse than the "my mate got 500 hp increase by fitting this" comments.

I'll keep you posted on the progress and hopefully get some data from rolling road time.

Jeff