Dell Orto carbs on Norton?
- Thread starter Jagbruno
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Yes, I know that BMW's, Guzzi's and Ducati's are running very well on big Dell Orto carbs.
But my original question was very specifically about my Norton 850 with splayed manifolds.
A friend of mine, who has been racing Norton 750 sidecars forever, has tried larger Amal mkII's (33, 34 and 36mm) and reckons his engine works best with 'ordinary' 32 MkI's or 33MkII's but NOT with the 34 or 36mm. Obviously this maybe different with the Dell Orto's because (or not) of the accelerator pump.
But my original question was very specifically about my Norton 850 with splayed manifolds.
A friend of mine, who has been racing Norton 750 sidecars forever, has tried larger Amal mkII's (33, 34 and 36mm) and reckons his engine works best with 'ordinary' 32 MkI's or 33MkII's but NOT with the 34 or 36mm. Obviously this maybe different with the Dell Orto's because (or not) of the accelerator pump.
i see you are in brussels wich is near to me (aalst)
i have run 32 dellortos on a 850 , they were good but no better than amals
if interessed you could try my manifolds and jetting i used 20 years ago
do not expect a big gain by using them , for that you need flatslides
like Frank (jordens) we tried all kind of carb sizes ( even a weber ) but found amals to be both easy and good for a norton engine
remember the first ducati 750 round cases had amals (30mm) and performed very well but unlucky wore rather quickly ( the carbs that is )
i have run 32 dellortos on a 850 , they were good but no better than amals
if interessed you could try my manifolds and jetting i used 20 years ago
do not expect a big gain by using them , for that you need flatslides
like Frank (jordens) we tried all kind of carb sizes ( even a weber ) but found amals to be both easy and good for a norton engine
remember the first ducati 750 round cases had amals (30mm) and performed very well but unlucky wore rather quickly ( the carbs that is )
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Goiedag!
Well, my Amal work well, very well even, except when starting from cold in the winter. I am not after an increase in performance (my bike was clocked at about 210km/h on the Dijon circuit straight) but easier start and more stable tick-over. I would be interested to know your jetting and have a look at your manifolds to see if they are similar to mine.
Bedankt et bonne journée,
Bruno
Well, my Amal work well, very well even, except when starting from cold in the winter. I am not after an increase in performance (my bike was clocked at about 210km/h on the Dijon circuit straight) but easier start and more stable tick-over. I would be interested to know your jetting and have a look at your manifolds to see if they are similar to mine.
Bedankt et bonne journée,
Bruno
milfordite
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I ran 36mm Dellorto's on my Norton race bike with good result. The bike has a Maney head, cam and exhaust system which made a difference for sure. Herb Becker ran 40mm Mikuni's on one of his bikes back in the day.
I have PHF's on the guzzi. Biggest problem is the weight of the throttle. Use lighter springs and the buggers won't close very quickly.
While they have well calibrated start and idle circuits, they are prone to blocking.
None of these is a Norton specific difficulty.
While they have well calibrated start and idle circuits, they are prone to blocking.
None of these is a Norton specific difficulty.
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lcrken said:I used a pair of 34 mm Dellortos for years on my featherbed race bike with 750 Commando engine. Loved them. I did have to trim the slides a bit to get good throttle response, but that was with open megaphone exhausts. Might work fine with stock slides for a street bike with silencers. If you decide to go with something similar, I can dig up my old jetting info. You can see them pretty well in this picture.
Ken
Very nice bike, Ken - I'd love to own it. I'd always change the needle jet sizes and needle tapers before I would ever trim the slides
lcrken
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acotrel said:
Thanks, Alan. I had a lot of good years racing it. I'm planning to eventually convert it back to a café style bike for the street, which is what it was when I bought it back in '84. Lately it's been doing duty as a landspeed bike at Bonneville and the dry lakes here, but this is probably the last year for it to be in that role.
I sort of agree with your comment about sorting the slide cutaway last, and that's how I usually proceed. And in this case I did sort out all the other bits first, and then adjusted the slide cutaway. But main jets, needle jets, needles, pilot jets, and slide cutout all affect different ranges of carburetion, although there is overlap. If the carb needs a different slide cutaway, changing the needle tapers and jets isn't going to work as well as getting the right slide cutaway. On a race bike, the throttle response just off of idle (where the slide cutaway has the most influence) is not as critical as on a street bike, and frequently only gets sorted out enough to make the bike rideable. But I had years to develop this bike, so had plenty of time to get it right.
Ken
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lcrken said:I used a pair of 34 mm Dellortos for years on my featherbed race bike with 750 Commando engine. Loved them. I did have to trim the slides a bit to get good throttle response, but that was with open megaphone exhausts. Might work fine with stock slides for a street bike with silencers. If you decide to go with something similar, I can dig up my old jetting info. You can see them pretty well in this picture.
Ken
I'd be interested to know where the splayed manifolds came from.
I have a pair of 34mm Dellortos that i tried on my Commando but they were too close together, and although they worked well on the dyno, ( a couple of extra horsepower over the previous 36mm Amals ) I had a load of hassles getting them to run well at small throttle openings. I had the slides machined from 40 to 55 .
Fast Eddie
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I've got zero experience with Dellorto carbs!
Nevertheless, I can't see why 36mm pumpers would harm anything provided your port size remains unchanged and you simply taper the manifold, or as Comnoz showed, radius the entry to the port. It's the port size that matters for charge velocity.
Norton advised 36mm MK2s In their tuning guide didn't they? And they weren't pumpers.
CNW sell the FCRs in 35mm, I have these and they perform absolutely splendidly in every respect.
Carbs can be fickle though. I had a 900 Nourish racer that gave far better power with 1000 series MK1 carbs (almost the same as stock concentrics but bigger) than it did on MK2 smoothbores. Both were 38mm. The smoothbores are a far superior carb, and did give something like 1-2 BHP more at peak, just less everywhere else.
Nevertheless, I can't see why 36mm pumpers would harm anything provided your port size remains unchanged and you simply taper the manifold, or as Comnoz showed, radius the entry to the port. It's the port size that matters for charge velocity.
Norton advised 36mm MK2s In their tuning guide didn't they? And they weren't pumpers.
CNW sell the FCRs in 35mm, I have these and they perform absolutely splendidly in every respect.
Carbs can be fickle though. I had a 900 Nourish racer that gave far better power with 1000 series MK1 carbs (almost the same as stock concentrics but bigger) than it did on MK2 smoothbores. Both were 38mm. The smoothbores are a far superior carb, and did give something like 1-2 BHP more at peak, just less everywhere else.
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Hello Pommie John, not sure who makes them, but Allen Performance in the UK sells Mikuni kits with those. But a friend of mine ordered just the manifolds, without the carbs.
You should ask for David:
http://www.allensperformance.co.uk/contact/
You should ask for David:
http://www.allensperformance.co.uk/contact/
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Jagbruno said:
Great! Thanks. I have split the pair now and I have one dell on my Honda XL250 and one as a single carb on the Commando. However it seems a bit sluggish with just the single carb so I'd like to go back to a twin set up and the Dells make sense. I'll just have to find a suitable carb for the Honda now.
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