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

[keithwwalker]

This is not an active post, but I thought I would mention that purely on an information basis, Sudco in the USA has a wealth of information on Mikuni (sidedraft) and Keihin (downdraft FCR type) carburettors.

Most of the bike carbs do not have accelerator pumps, but there are models that do, which I assume would be best for translation to automotive use.

Best bet is to find the carbs you desire, then buy them used from a wrecked bike, then modify to suit with different jets and needles.

The last time I saw bike carbs on a car they were on a N600 Honda!

[Testament]

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

I know personally two freinds who have gone down this route, one on a 1600 kent in a mk1 escort and the other on a 1300cc mazda in an 808 sedan. In both cases it was more cost, and doing something "different" (hey why not) while gaining some level of performance that drove the decision. most of these bike carbs are fitted with a rubber or silicone joiner so manifolds are very easy to make, and if you keep an eye out you can get a bargain on the carbs compared to DCOE's or similar which are more static in price and often people want high prices even for carbs in need of alot of work in this part of the world. Being CV type the mid range tuning generally looks after itself as well which is a minor advantage in soem respects.

But you are quite right they are not a magic bullet, just another carb. Also generally somewhat limited in size so usually not suitable when you start to get up to two litre engines - I find a crude but effective way of looking at it is carb is going to flow enough air/fuel for up to 'x' hp, so if a bike the carbs were on was rated at 100hp, your not going to get away with using them on any other engine to make a heck of alot more power, maybe up to 20% more at best or something like that. Of course this is simplistic and ignoring idle requirements, but you get the idea.

[WhizzMan]

I find a crude but effective way of looking at it is carb is going to flow enough air/fuel for up to 'x' hp, so if a bike the carbs were on was rated at 100hp, your not going to get away with using them on any other engine to make a heck of alot more power, maybe up to 20% more at best or something like that. Of course this is simplistic and ignoring idle requirements, but you get the idea.

I've been looking for suitable bike carburetors for a Renault 17 with a 1700 engine in it. I did not just limit my search to BHP of the donor, but also to displacement per cylinder per stroke and RPM range. With displacement I don't just mean "static" displacement, but the actual amount of air being taken in by the engine. If you look at the power figures of bikes that have a lot of displacement, you may find that the carbs are capable of running higher RPM numbers but may not always give enough power at the RPMs the car engine requires. If the bike engine takes twice the RPMs to get the same amount of BHP, you may still have a mismatch. If you go for bike carbs on your 4 in line car, don't automatically rule out V-twin donors. The big chopper style bikes sometimes have interesting carburetors on them, even if you have to fabricate the throttle linkage yourself.

As to the R17, no, I didn't find anything yet that the owner fancied and he's toying with multiple ideas, so the last word hasn't been spoken about these. This same engine was used in Alpines as well, so there are plenty of options for it.

[turbofiat]

I don't know if you would call this a superbike carb but I briefly experimented with a Zenith 38mm carb from a Harley Davidson on my Yugo.

Zenith.jpg (26.73 KiB) Viewed 1442 times

As you can see if has a manual choke but an accelerator pump.

I had to make an adapter using a 90 well pipe to bolt to the stock manifold which placed the carb above the exhaust manifold. I built a drip tray to go underneath it because I wasn't too keen about the possibilty of gasoline dripping on a hot exhaust manifold. Especially since this was a blow through application.

The reason I chose this carb was because I knew a guy who turbocharged a '78 Harley bike using this carb. His turbo came from a Ford Escort. He said these carbs could be easily tuned because it had an adjustable main jet (needle valve). If you need more fuel just turn the screw.

Looks to me like blowing through a single barrel carb would be hard to tune compared to a progressive 2 barrel carb.

For whatever reason I couldn't get the carb to idle correctly on my car. The idle had a nasty lope and the engine would just shut off as soon as it hit boost. I look back now and I'm sure the problem had something to do with the fuel bowl vent not being properly set up. I know that explains the engine shutting down but not sure if it was causing the deal with the idle speed going up and down.

I ended up using the Weber 32 DFTA that came with the 1100 engine. I didn't like the looks of this setup anyway. It looked horrible.

I still have the carb and may revist the possibilty of reusing it on my 131 if I ever get around to turbocharging it one of these days.

Rather than making an adapter to bolt to the stock intake manifold, I may just make a manifold to accept it.

Question: Has anyone ever seen an intake manifold for a single side draft carb that is made for a twin cam? I know there is a manifold to accept a pair of DCOEs but they are rare here in this US because the carbs interfer with the brake booster and master cylinder being our cars are left hand drive. But I think a single carb would clear the braking system.

One of my Fiat friends told me he saw a Triumph Spitfire with a turbo and this same carb at a local car show. I have yet to see it.

[Urbancamo]

Question: Has anyone ever seen an intake manifold for a single side draft carb that is made for a twin cam? I know there is a manifold to accept a pair of DCOEs but they are rare here in this US because the carbs interfer with the brake booster and master cylinder being our cars are left hand drive. But I think a single carb would clear the braking system.

I've seen.

In my country is car racing class where you are not allowed to use more than 1 carb. Fiat TC is the most common engine on this "sports".

70a7854854a08ba7edacf22ed5d1eb8a (Small).jpg (34.15 KiB) Viewed 1436 times

Very popular one, made from steel. Pretty reasonable priced too.

080307 017p.jpg (8.29 KiB) Viewed 1436 times

One of my favorite carb stuff suppliers has one cast one in stock, very rare!

[turbofiat]

Is this for a DCOE? Any chance something like that would fit a 131 twin cam? Looks quite long without the carb.

I forgot that I have a Solex 40mm side draft (somewhere). I bought it off an internet auction site several years ago. The price seemed right at the time and I had plans for it but never used it. The body looks like it's a copy of a Weber DCOE 40 but I'm not sure. Would this carb be called a "Solex 40 ADDHE"?

[Urbancamo]

Upper one is very long as it's meant for rear engined car. They use very long manifolds to gain torque...

Both manifolds of course have this common dual carb flange, so it will fit Weber DCOE, Dellorto DHLA, Solex ADDHE, SK-Racing, Mikuni PHH etc...

No idea for fitment for 131, upper one maybe not, lower one maybe? Maybe 131 enthusiats would tell how much there is space available in LHD version.