Dell Orto carbs on Norton?

Jagbruno · Feb 21, 2017

Hello all,
I am toying with the idea of using a pair of Dell Orto PHF 32 carburettors on my Featherbed Commando 850 road/racer. It is a fast engine with much lightened crankshaft and dunstall rockers, PW3 cams etc.
At the moment it runs very well with twin 32mm Amal MkI's, 260 main jets for road, 290 for tracks.
My problem is that when the weather is fresh, the engine can be a bit of a pig to kick start from cold as I removed the badly designed starter circuits. When the weather is good, or when the engine is hot or has run even quite a few hours earlier, it starts first kick.

I happen to have a pair of Dell Orto PHF 32 (coming from a Ducati 750 bevel drive) which are excellent carburettors with a very good separate starting circuit. I have used them on BMW airheads with great success.

Is there anyone out there who has ever tried those carbs on a Norton engine, and if yes with what results and which configuration?

(I am aware that Dell Orto carbs are wider than Amals but I have splayed inlet manifolds and all the space needed within my Featherbed frame to install them)

Thank you in advance,

Bruno

triumph2 · Feb 21, 2017

Ron Wood used Dellorto carbs on his big tube flat tracker in the '70s (The dirt track limousine) with great success though I think they were larger than 32mm?

Jagbruno · Feb 21, 2017

Well, I have larger carbs available, but I want to keep torque at low revs, afaIk increasing carbs indeed produces more power on top but is very detrimental for normal (or fast...) road use.

lcrken · Feb 21, 2017

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

Jagbruno · Feb 21, 2017

Thanks Ken,

At the moment, I have Dunstall silencers :roll: on the bike, I will probably replace them with Peashooters at one point, but certainly not with megas. Although my engine is a 850 with PW3 cams as opposed to your 750, your information might prove useful! So, if it isn't too much trouble I would love to have a look at your jetting data.
Can you remember what size your carbs were?

All the Best and thank you in advance,

Bruno

Rosey · Feb 21, 2017

Bruno
Hi I adapted a pair of 32mm Dellortos to my Triton 750 in the late 70.s ,much harder then than now as there was internet and no info around. Can be done , spares over there would be no problem.
I still have the Triton so can give you the jetting I used in that.

The splayed Triumph head made fitting easy but the Norton head is harder due to the width of the carbs. I did see a local Norton that had Dellortos 32's on it .It started first kick and just sat there and idled nicely.
What he did for mainfolds was use a pair of Norton ones and a pair of the Ducati ones (as they are clamp on type).Cut the amal flange off the norton manifold and the clamp on section off the Ducati manifold.
They were welded together and made to splay out for clearance between the carb bodies.But don't forget about airfilters,use K&N Part no RC 1820.
Don't forget to use the tufnol insulator between the head and the manifolds.

Brett

concours · Feb 21, 2017

https://www.denniskirk.com/llp-mfg/butt ... d/1861.sku

lcrken · Feb 21, 2017

Jagbruno said:
Thanks Ken,

At the moment, I have Dunstall silencers :roll: on the bike, I will probably replace them with Peashooters at one point, but certainly not with megas. Although my engine is a 850 with PW3 cams as opposed to your 750, your information might prove useful! So, if it isn't too much trouble I would love to have a look at your jetting data.
Can you remember what size your carbs were?

All the Best and thank you in advance,

Bruno

The carbs were 34 mm, with the accelerator pumps removed to meet AHRMA rules. My usual race jetting was a 135 main jet, 65 pilot jet, needle clip in second groove from top, and a "54" slide. That's a 60 slide with 0.6 mm removed off the bottom. I occasionally used a 128 main jet for higher altitudes, like Steamboat and Park City, and sometimes a 140 main jet for long tracks like Daytona or on really cold days. That's all with 1 5/8" pipes with open megaphone exhausts and no air cleaners. The engines were full race spec 750s, with 10.5 to 11.4 compression ratios, Axtell ported heads, and mostly Axtell cams. Hope this info is of some use to you.

Ken

Jagbruno · Feb 21, 2017

Brett,

Thank you for the info. In fact I have resolved the manifold issue before it even became one...my bike as it stands now is equiped with 32mm Amals MkI's mounted on splayed alloy manifolds coupled to nitrile adaptors, identical to the ones used on twin Mikuni kits. This allows me to remove or install the carbs in mere seconds. Because of that, it is very easy to try out different types of carbs.

Jagbruno · Feb 21, 2017

Ken,

Thank you, much appreciated!!

ashman · Feb 21, 2017

In 1980 when I first built my hot 850 in the Featherbed frame I brought a new set of 32 Dellorto pumpers for it I used the Amal manafolds cut in half and cut the Dellorto manafolds in half and weld then together but on a angle so the carbs stuck away from each other, they worked very well when warmed up but was a pig to start when cold, I used them for a few months, mucked around with the jets and fiddled with the pumps, my 850 has a lot of work done on the motor and was built for the Featherbed ( balanced crank, hot cam, lots of port work on the head etc) it ran great when going but like I said was a pig to start when cold, I ended up putting the Amals back on with new Amals and it stayed like that till about 6 years ago I put a set of Jims PWKs on it, if you get the jetting right the Dellortos are a great carb, in my days there was no internet so was harder getting info for the Dellortos at the time and me not being a carbie person at the time, but with the pumps adjusted right you hit the throttle it jumped and had no problems lifting the front wheel in first and second gear, I run 270 jets in my Amals for the road.

Ashley

Fullauto · Feb 21, 2017

My other Norton had 36 Dell Ortos on it when I got it. After a bit of fiddling it started first kick, hot or cold with A Joe Hunt magneto. It had other issues but they worked fine.

ashman · Feb 21, 2017

Fullauto said:
My other Norton had 36 Dell Ortos on it when I got it. After a bit of fiddling it started first kick, hot or cold with A Joe Hunt magneto. It had other issues but they worked fine.

I think they would work great with the Joe Hunt maggie, I have only had my JH on for the last 6 years now, a JH and a set of pumpers, but the fun police will slow you down, times are a changing and not for the good fun we use to have.

Ashley

Jagbruno · Feb 21, 2017

Ashley, thank you.

Fullauto, I would have thought that 36mm carbs would be very big for a Norton? I can see how they would work great @ wot but how was the bike running at low and medium rpm's ? Was it a race bike or a road bike?

Best,

Bruno

pantah_good · Feb 21, 2017

The 898cc BMW R90S came stock with 38mm Dellorto's, and it is very well behaved. You have your choice of the tickler primer like Amal's have or flip lever chokes. And accelerator pumps or not. Their main drawback may be that they are physically rather large, but I always thought they worked great on my R90S and Ducati's.
Bill

Rohan · Feb 21, 2017

pantah_good said:
The 898cc BMW R90S came stock with 38mm Dellorto's,

My R90S (project) has 36mm pumper Dellortos. Has it lost 2mm somewhere ??

Guzzi LeMans also has 36 mm pumpers, idled very well - sometimes.....

I have no idea how you'd squeeze those into a Commando frame.
Obviously featherbeds offer more scope.

xbacksideslider · Feb 21, 2017

I love those carbs; especially the pumps. That shot really helps at that moment when the throttles are whacked open but the inertia of the air means the mixture can't catch up. Also, that shot allows a big carb to "pass" for a smaller one.

Ran 'em on singles for years and of course they came on the 1972 Ducati Sport that I sold long ago, stupidly.

I've got two right hand 32s on the shelf; if I had a left handed one, a set would be on my Commando now.

Fullauto · Feb 21, 2017

Jagbruno said:
Ashley, thank you.

Fullauto, I would have thought that 36mm carbs would be very big for a Norton? I can see how they would work great @ wot but how was the bike running at low and medium rpm's ? Was it a race bike or a road bike?

Best,

Bruno

They worked fine from off idle up. Never got into the top end because of the horrific vibration. But, everywhere else they were fine. A road bike.

Fullauto · Feb 21, 2017

Rohan said:
pantah_good said:

The 898cc BMW R90S came stock with 38mm Dellorto's,

Click to expand...

My R90S (project) has 36mm pumper Dellortos. Has it lost 2mm somewhere ??

Guzzi LeMans also has 36 mm pumpers, idled very well - sometimes.....

I have no idea how you'd squeeze those into a Commando frame.
Obviously featherbeds offer more scope.

Yep. Definitely 38s were standard.

The 36s fit no probs with a splayed manifold. Looks like they were modded from the original Pantah (?) manifolds.

bluto · Feb 21, 2017

pantah_good said:
The 898cc BMW R90S came stock with 38mm Dellorto's, and it is very well behaved. You have your choice of the tickler primer like Amal's have or flip lever chokes. And accelerator pumps or not. Their main drawback may be that they are physically rather large, but I always thought they worked great on my R90S and Ducati's.
Bill

+1, had them on a R90S too, they worked great and were 100% trouble free after many miles...

Dell Orto carbs on Norton?

Similar threads