15 replies to this topic

[deakin1988]

Hi can someone tell me why do people put motorcycle carbs on minis. Why are there better and what makes them better
Thank you

[Scoop77]

I've only had experience of using R1 and ZX9 carbs on bigger engines but they are a relatively easy and cheap way of getting plenty of air and fuel in. Once set up they hardly ever go out and sound great. The only pain in fitting them is splitting them and mating them to a manifold which puts the float bowls at the right angle. Although not cheap I used Bogg Bros on both occasions but for a mini with only two inlets it should be easier to manufacture apart from the lack of room (if no carb box fitted).
I'd have thought something in the 600 to 750cc range would be good.

[Spud_133]

They're the modern version of an su carb, and is debatable whether or not they're a good replacement when comparing the work involved, if comparing a su/ pair of su's or weber to the bike carbs.

[Captain Mainwaring]

The original crossflow heads used Amal bike carbs.

[YIANO]

Having an r1 mini myself I've seen people using r1 carbs on a series engines and don't see the point either. A series engines on bike carbs don't sound like a bike they are a pain to install and they hate running on aftermarket filters or open ram pipes.
R1 carbs or Indeed bike carbs have specific fuel angle requirements they are designed to run with a pressurised airbox have variable needle heights two jets to deal with and are far trickier to set up than an su carb would ever be .
I've spent months trying to fuel my bike engined mini correctly altering needles ,needle height via shimming main jet size pilot jet size etc and concluded that the factory setup is unbeatable ie pressurised factory airbox filter and installation parts .
What I'm trying to illustrate here is how complicated the bike carbs are to set up even on the engine thy were designed for despite being so visually simple and ultimately extremely application dependant .
If people think chucking some r1 carbs or similar on a 1275 with sock filters and drilling the main jets to some oversize figure will make their engine rev like a bike and add 10 bhp ,well it won't at all .
The best carbs for a mini engine are su , purely because they offer a straight forward set up ,are proven to work ,familiar with tuners and extremely effective at metering air and fuel to the specific engine requirements or package they were designed for.
So people , don't waste your money ,bike carbs are for bike engines and very difficult to optimise for other engines
With regards to factory 8ports running Amal carbs its because that particular carb setup was compact and would fit within the allocated
space

[Gr4h4m]

Maybe you need a professional operator to set them up....

My single works much better than any of the su's I have tried, which are mostly all worn out but then each to their own.

[Rob Jones]

I have bike carbs on my Mini from a Yamaha 850DTM (2 cylinder bike) with a 38mm choke size. They are mounted on a modified SU manifold to get the right angle, with Pipercross socks and they work fine.

Granted the modifying of the manifold and respacing of the carbs can be difficult, but taking time and thinking about it can be enjoyable.

As for being difficult to set up, you ask your local rolling road operator if he has any experience of them, if not ring round.

[DILLIGAF]

Not all bikes have pressurised air boxes, problems caused by this are usually related to the air drillings in the carbs, these are usually on the edges of the edge of the carbs bellmouth...........

[YIANO]

Dude I used the r1 carbs as an example which are the most popular choice for conversion and the air box is designed to deliver a large volume of pressurised air to the carbs .
Secondly your referring to blocking off the main air jets near the bell mouth to compensate for lack of airbox and limit the vacuum slides have you tried doing this ? I have mate .
Leave bike carbs to bike engines and save your money and time

[YIANO]

Fair play to people who are happy with the results of their conversion.a single carb is easy to deal with compared to four.
Anyone dynoed their engine before and after are their any real gains after the cost factor ?

[DILLIGAF]

Dude I used the r1 carbs as an example which are the most popular choice for conversion and the air box is designed to deliver a large volume of pressurised air to the carbs .
Secondly your referring to blocking off the main air jets near the bell mouth to compensate for lack of airbox and limit the vacuum slides have you tried doing this ? I have mate .
Leave bike carbs to bike engines and save your money and time

 
LMAO fitted several sets of bike carbs to cars ranging from Minis to 2.2 litre capri's and since when has the main jet been on the edge of a the carbs bellmouth.........
 
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[YIANO]

Air jet i said are you deaf ? the main jet is located inside the float bowl underneath each carb, and yes I'm an automotive engineer buddy so I know what I'm doing . Agree to disagree here I can't be arsed with this . Obviously it is you who doesn't know how these carbs work if you did youd understand what im saying and why. ive tested different setups in the workshop running different filter setups etc and stand bywhat i said.

[R1mini]

Various motorbike carbs including R1's have been sucessfully used many times on pintos, zetecs, crossflows, etc, have a look on locostbuilders site, an A series should be no different.

 

YIANO I followed your thread and found it interesting, did you ever get the carbs professionally set up by someone who knows what they are doing?

 

Cheers

David

[DILLIGAF]

So what have you tried and what problems did you encounter ?

[YIANO]

Yes I did set them up in the end , After much testing 7 different sets of main jets 2 sets of needles and time it runs awesome . I'm using a hyabusa airbox now and the mini is seriously quick :)