carb choices

[Nortonash]

My rotary enthusiasm has recently been reignited and because of this I will be picking brains of the rotary collective on here as info is pretty hard to come by, especially good info Thanks to Richard I have sorted the water pump question now it is carbs. For ease I was thinking about using SU's, also because I have some new ones LOL. Is there a better alternative ? On a Commander engine is it possible/practical to mount them facing forward instead of backwards? I wont be using a Commander spineframe so there would be space for an airbox at the front.

[Richard Negus]

I suppose it depends on how you're going to use the bike. Out-and-out performance needs bigger inlet ports and pipes, which means the housing butterflies are gone, as is the low speed driveability. Almost any carbs with throttles can be made to work. RC and RCW race bikes had U-shaped induction pipes with the carbs pointing forwards.If you need to keep low-speed driveability, then you need to keep the butterflies in, or very close to, the rotor housings. That in turn means the carbs have to be mounted further way without throttles, such as the SU's - or injector bodies.It might be feasible to mount injector bodies, with throttles, close to the engine and use recirculating fuel to keep them .R.

[Nortonash]

Thanks again Richard, what would we do without you on here ? I am looking at using a pair of twin plug housings, not sure if that makes any difference ? I love the idea of fuel injection but just think it would be too hard to set up. I havent seen my twin plug housings for ages, do they even have butterflies mounted in them ?

[Richard Negus]

Ash,No butterflies, just a short port with a square face with four M5 tapped holes.These are race-ported aero housings with bored-out ports and steel stub pipes inserted to locate the inlet pipe.

HCL4-33.jpg

A possible down side of the aero housings is that the inlet ports are closer to horizontal, putting the inlet pipe closer to the gearbox and needing a sharper bend in the pipe. Not impossible though.Exhaust flange shape & position is the same as the motorcycle.R.

[Charles Wilson]

Richard!Did you ever look at any of the "Variable Overlap" devices that were lying around?Plz see the Froede patent posted elsewhere here.Lotsa good stuff! It doesn't have to be a butterfly and when the device is opened, there is nothing in the way.CW

[spondonash]

Ash,No butterflies, just a short port with a square face with four M5 tapped holes.These are race-ported aero housings with bored-out ports and steel stub pipes inserted to locate the inlet pipe.

HCL4-33.jpg

A possible down side of the aero housings is that the inlet ports are closer to horizontal, putting the inlet pipe closer to the gearbox and needing a sharper bend in the pipe. Not impossible though.Exhaust flange shape & position is the same as the motorcycle.R.

Thanks again Richard, my aero housings arent like that, the inlet ports are very similar to the bike housings and dont exit horizontally like that, they are angled and the machined face is closer to the housing itself, if that makes sense.

[Richard Negus]

Aah! Like these perhaps?

P60T-42-28.jpg

Sand-cast twin-plug prototypes, with a single rib across the top face of the casting, rather than two ribs of the die-cast production housings. Some of those are machined to suit a butterfly and spindle too.A photo of yours might be a reminder for me, and others.The die for production rotor housings had several interchangeable sections so it could produce:.motorcycle housings, single plug, two dowel, butterfly, push-in inlet pipe.aero housings, twin plug, five dowel, no butterfly, square inlet flange.military housings, no plugs, indirect injector, five dowel, square inlet flange (only a few prototypes produced)It could also mix'n'match any of the above, but I don't believe any twin plug, butterfly castings were ever made.R.

[Nortonash]

Well they are more like those ones Richard but not exactly. They are still in storage at the moment but as soon as I dig them out I will take a photo.

[Wayne]

Hi AshNow how are you getting the air out of the intermediate plate, if you are using ventury/extraction its difficult using cv carbs on the commander spondon beam frame engine. it can be done but the 2-1/2" hose has to come over the top of the carbs requiring modifing the underside of the tank, you also need short inlet tubes mounted verticaly. it can be done, mark simpsons Rcw is how to do it and on my bike as recived how not to do it. I will be fitting the correct amal smooth bores and induction tubes, but on a road bike i think it would be unriderble with amals in trafic.I have a weber injection unit that came with a load of norton race stuff and it looks like it would fit aro housings, but think it would take big £ to develope.Mark uses twin plug race housings with droped plugs,seats, race plugs are £140 for a set of 4, on twin plug race housings it gives an extra 6 bhp, (at the engine). Incidently all the aro housings i have been offerd are all A grade or B grade, Regards Wayne

[gripper]

Bill Meredith's air cooled has the airflow reversed as per the Commander and has two forward facing amal smoothbores. He has to run a twostroke fuel mix to lube the tips and the mains are fed directly with the extractor exhaust burning the residue. I think he gets about 25 mpg but it goes like stink. I've seen his whole exhaust bright orange from engine to tailpipe.