Topic: Dellorto Carbs

[valt]

Alright I have some questions for you racing guys. I am building another cb750 and I already have ARD magneto for it. I had planned on using a drouin supercharger on this bike as well. But after some reading it seems that these are very finiky and hard to run on a street bike. I intend to ride this bike a lot so it needs to be something I can actually use. I have no problem working on and fixing problems as they come but I need parts to be available.

So that leads to the Dellorto carbs. I have seen this setup on several other bikes out there and it seemed to be fairly common thing to do back in the day. What I want to know is first of all what size Dellortos were they using (from some reading it looks like they were mostly 35s?). Secondly where is the best place to find parts for these carbs, jets and what not. Lastly how did they mount? I have seen several different manifolds, but what I haven't seen is if the carbs are supported in some other way besides hanging off the intake.

Anyways for your trouble here is a pic of the bike I'm building.

[scottly]

Here's something to get you started:
http://forums.sohc4.net/index.php?topic=68065.0

[valt]

Here's something to get you started:
http://forums.sohc4.net/index.php?topic=68065.0

Ahhhh thank you, I knew I had seen that thread before. I searched but I guess I didn't search the proper term.

[754]

 Here is a set of Dell,s I have,just added the ignition today..looks pretty trick. I must say..

[754]

Another.. . 

[Retro Rocket]

Which are easier to set up guys, Webers or Dellorto's..?  There seems to be general support on both sides but i hear Webers are easier to get parts for and are easier to set up...  I want to use Webers on my 900cc build...

[754]

 I never ran the Dell,s..I got more jetting for Webers, and started with a running set.
 Be careful with the Dells and stock frame, may be clearance issues where the brass nut is on top.

[MRieck]

Which are easier to set up guys, Webers or Dellorto's..?  There seems to be general support on both sides but i hear Webers are easier to get parts for and are easier to set up...  I want to use Webers on my 900cc build...

RS-34's Mick

[johno]

Hi Mick,
Sounds like the ol nostalga trip coming up !

I have used all three, my take is any modern carby set up is better than the classics , they can be adjusted to get a better shot at the inlet than the side drafts, lighter, simpler cable set up.   I wouldnt run 34 mm for anything other  than racing, they wallow a bit mid range especially with 900 and smaller, I like 32mm for anything on the road and medium displacement, just snappier to ride around town.

With regards to the the classics side drafts my preference is for webber, only because of all the maniflds available I like the RC manifold as its a straighter shot at the port and flows better; these manifolds suit the webbers.

I have run Dellorto's on a Lynx manifold which had the alloy framed rubber manifold that pulsed like crazy and I had to be super carefull to seal it well, also the rubber manifolds were not that UV resistant and after about 2 years started splitting and I swapped to the webbers.

They all work OK its just horses for courses     Its what floats your boat baby !
cheers Johno

[MRieck]

  I wouldnt run 34 mm for anything other  than racing, they wallow a bit mid range especially with 900 and smaller, I like 32mm for anything on the road and medium displacement, just snappier to ride around town.

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
  The last older carbs I worked with were the Mikuni Weber copies. There were clearance issues. They worked OK but that was a very long time ago.

[valt]

Yah it seems that I am leaning towards the webers as they are easier to come by. As for the manifold I am thinking I will just have someone make me one. The old manifolds are very hard to come by, but I will keep my eye out for them.

Now if I can only find some DCOE 40s that aren't 700 dollars I will be in business!

[754]

 Dells and Webers use same manifolds. New Dcoe,s should be 900.00 or less, but are probably not made in Italy.

[Retro Rocket]

Which are easier to set up guys, Webers or Dellorto's..?  There seems to be general support on both sides but i hear Webers are easier to get parts for and are easier to set up...  I want to use Webers on my 900cc build...

RS-34's Mick

Gday Mike, i plan on using the RS34's on the 970, i have an unused weber manifold and was just wanting to try something different, i may just sell it and go with the RS's instead,  you'll like the fuel injection set up that's going on the billet 1000 bike......

[MRieck]

Which are easier to set up guys, Webers or Dellorto's..?  There seems to be general support on both sides but i hear Webers are easier to get parts for and are easier to set up...  I want to use Webers on my 900cc build...

RS-34's Mick

Gday Mike, i plan on using the RS34's on the 970, i have an unused weber manifold and was just wanting to try something different, i may just sell it and go with the RS's instead,  you'll like the fuel injection set up that's going on the billet 1000 bike......

Now you are talking.

[Retro Rocket]

Sent you a PM Mike...

[johno]

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


 

[Retro Rocket]

Johno, the RS34'a have great accelerator pumps that have tons of adjustability, actually as far as i  {and others here} am concerned they are way more efficient for a street bike than CR's, lots more adjustment overall, thats the reason they work well on HIPO Honda's, they can be set up well for all stages of the rev range.     See, you can teach an old dog new tricks...

[johno]

Mick,
Its a hi tech world, your opinion on fuel efficiency is technically 100% correct as far as I'm concerned, just what I wanted to hear, I'm an old dog in a changing world.

Now for some old dog advice to Valt and yourself that may influence his choice of carbies.
I have shown my two bikes at two invitation only bike shows in Victoria, one is a stock bike in as good a condition as I can get, its my favourite,   the other modified engine, webbers and exhaust and really looks a bit ratty common to me
BUT

Only one bike gets people coming up to me to ask questions and want to spend time at the stand, the conversation always starts with the same question and it starts with W.

Only a few very focussed people in the big bad world of classic motorcycling worry about the fuel curves , my experience is 90 % just worry about what it looks like.   In my experience the two big head turners have been Webbers and Hilborn injection, evan though I know the modern carbs are more efficient, if your racing your bike Mick its a no brainer what to use and it aint webbers or delortos but if you want to get the old farts all fired up might be worth using  something classic.  So I guess if Valt keeps the thread going  we will find out what floats his boat.

I hate getting old Mick,  but #$%* there is a lot of us around, most of us dont drift through the corners much these days, I would rather go to show or race pits and talk about the good ol days
ciao Johno

[Retro Rocket]

Gday Johno, yeah, i see what you describe every time i go to a show, slightly unique is what i was going for here, after all, i'm going to sell this one once its run in and has some miles on it and i have seen some stupid money thrown at some less than perfect Honda's of late so i thought some old 70's bling may just help me grab a few more dollars. I'm saving all the High Tech stuff for the one i'm going to keep...funnily enough, i ran in to an old friend last night and spent a couple of hours over a cold one talking about the good old days...

[scottly]

on a street bike. I intend to ride this bike a lot so it needs to be something I can actually use.

The Webers will work great on the street. The setup work has already been done. I have gotten over 60 MPG on several occasions. I have no first hand experience with the Dels or other carbs mentioned on this thread, but I will once again state my belief that Webers are the finest carburetors ever made.

[johno]

 Captain Webber     what took you so long !   thought I was going to get beat up and was wondering when the cavalery would arrive 

They are definately the most flexible fuel mixers readily available hence they have won the heart of motor enthusiasts the world over cars bikes and boats alike.   
 easy peasy to adjust  chokes venturi size , emulsion tubes, mains, air corrections, pump shooters, idles all easily and quickly   most mechanics liked the flexibility to be adapted to anything in the 70's , certainly RC engineering made them iconic for Hondas.

Maybe its a way of us staying young at heart by living in the past ?

[scottly]

Not just flexible, the Webs do the best job of mixing the fuel with the air, IMHO, which is what counts. All motors have harmonics, whether carburated or injected; the trick is making them occur in the RPM range where they will do the most good. When the intake and exhaust tracts are in harmony, there will be a peak in the dyno curve.
Back in the Olden days, guys with two-stroke go-carts had variable length expansion chambers, to broaden the curve. Honda did the same type of thing by changing the volume of the exhaust on MX bikes in the '80s, with a centrifugally operated valve.
The main advantage with EFI is the intake runners can be twisted in ungodly shapes to achieve the optimum length for lower RPMs, without fear of fuel separation, as it is only air that has to go around tight corners.   

[754]

 When you have seven things you can change, jetting wise..should have an easier time getting rid of bad spots.

 I agree with Johnnie, looking good is part of the fun. Looking at RS 34,s, is a bit like looking at sportbike parts or ducatis...... But that is not what I want to ride..

[scottly]

I just remembered one of the things I never liked about the Dells: the accelerator pump diaphragms, compared to the pistons in the Webs. If/when the diaphragm cracks, tears, or ruptures, a replacement part is required. The brass Weber piston doesn't fail, and even if excessively worn can be compensated for with the discharge jet. (I've yet to see that happen, BTW. )   

[Tintop]

I'll join the Weber side.   If you have to / want to use a 'vintage carb'  nothing beats them for adjustability.  Getting parts for Webers is easy, Dellorto's a pain.