Johno...are you talking about round slide carbs? Flatslide smoothbores produce a much stronger signal and work very well on smaller displacement engines (down to 600cc on more modern engines). DoctorD is using them on his 836 and getting 88 RWHP with good midrange and torque. The last 600 carb models were up to 36mm flatslide CV's
Hi Mike,
Lucky guess mate
dont want to show my age but yes round slides.
I havent done any back to back dyno comparisons between the round slides and flats. I have only tried one set of flat slides on a speedway outfit with 1,000 cc and it left no doubt in my mind they make more hp. didnt do a dyno on the bike just plug checks and rider feedback. ( was an experienced rider, national champion Ken I'Ansen)
I hear what your saying re big carbs on modern bike work well ( eg 600c 36mm carbs) Racing and dyno the big numbers always come from the big carbs at peak RPM but it is something I dont encourage for say hot street bikes. My reasoning is that the modern motorcycles say 600cc are designed using an amazing data base computer which gives them the ability to use big carbs for top end but to make the bike ridable low down, they design amazing accoustics to control reversion and intake harmonics and use vacuam related carbs all to make a very nice ridable road bike for its capacity. With a 1969 honda with lots of aftermarket performance parts on there is not a lot of complex design done to get the nice hp and tq curves ( although Doc D goes close with hi attention to AF ratios) So what I see on the dyno sheets posted is lots of dips that show a comprimise at some particular RPM. Generally that comprimise gets more as the max numbers are chased, eg the numbers Doc D posts are interesting at 88hp and 58 tq but on his graphs the hp curve dip at 55 to 60mph
The fuel shooters get the blame but I feel its a result of the accoustics from the imbalance of the system design at that particular RPM creating the richness. Less fuel will help the cause but not the problem.
In a nutshell saying the bigger carb will get the ponies but usually not as nice to ride around town without the modern technology to optimise everything, the more mods and the bigger the carb the more the comprimises down the rev range. ( Ol Voxonda 836cc had 85hp 58.7 tq with just 31mm carbs ), without support of complex accoustics the smaller the carb, higher the velocity the quicker throttle responce, Rob 's would be nice for his style of racing and for the road.
I arrived at the 32mm being my favourite carb size from the old days by back to back changing round slide carbs and changing venturis on the webbers etc so I graciously accept I am probably a jibbering dinosour and not up to date. But for a street bike I must say this, in my life I have never seen a street bike or race bike fort that matter that runs at max RPM. its all about getting from one RPM to another RPM and so for me and a street bike its about snappy throttle responce.
I feel a bit embarressed Mike, In the scheme of things I may have explained things in a complex way to make a simple point, captain conservative is my middle name.
cheers Johno
