Amal Premiers on 1966 Atlas
- Thread starter Beach
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No one is answering so I'll give it a try. The Concentrics came as standard fitment on the 67 and 68 650ss so I don't see why they wouldn't work well on an Atlas. Also, the early Commando engine was essentially an Atlas engine and it was fitted with 30 mm Concentrics. So you might ask in the Commando section as to what cutaway, jetting etc was used on the 68 Commandos. I might have that info here somewhere, will have a look.
The carbs fitted to the late 650ss were 30mm in size.
The twin 930s on the 650 work like a hot damn, the bike breaks the ton with ease and has very good throttle response at all rpm. The late 650 is sometimes rated at 52 HP vs 49 for the earlier bikes which had smaller monoblocks. I've always/assumed the difference was due to the carbs as there is no other performance type change between early and late engines.
Glen
The carbs fitted to the late 650ss were 30mm in size.
The twin 930s on the 650 work like a hot damn, the bike breaks the ton with ease and has very good throttle response at all rpm. The late 650 is sometimes rated at 52 HP vs 49 for the earlier bikes which had smaller monoblocks. I've always/assumed the difference was due to the carbs as there is no other performance type change between early and late engines.
Glen
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Hey Bill
It would be interesting to try a set. I'd use 30's on a street engine. To compare to commando it will require checking the fuel level using a sight tube. The commando carb is 10 degrees of tilt and the atlas is 18 degrees. I have never been convinced the float is 100% linear in response to fuel level V.S. angle.
Since the throat size does not affect fuel level, I may try a test on my friends premiers. I got him a set of 32's and before we put them on I can do a fuel test since I have a pair of bowl drain test tubes and will see how accurate they track as the angle changes. :mrgreen:
It would be interesting to try a set. I'd use 30's on a street engine. To compare to commando it will require checking the fuel level using a sight tube. The commando carb is 10 degrees of tilt and the atlas is 18 degrees. I have never been convinced the float is 100% linear in response to fuel level V.S. angle.
Since the throat size does not affect fuel level, I may try a test on my friends premiers. I got him a set of 32's and before we put them on I can do a fuel test since I have a pair of bowl drain test tubes and will see how accurate they track as the angle changes. :mrgreen:
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750 engines from 121007-on used 930 concentrics (every P11 and Atlas-N15-G15 from mid-model year 1967 on). I don't see why you couldn't use them on a '66 motor.
Type: 930/300
Main Jet: 220
Needle Jet: 106
Slide Cutaway: 3
These specs are what Walridge would give you for an N15
Type: 930/300
Main Jet: 220
Needle Jet: 106
Slide Cutaway: 3
These specs are what Walridge would give you for an N15
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I'm bumping this thread because I'm in the process of installing a set of 930 Premiers on my 64 Atlas.
The bike had a single Concentric, which may be original to the bike, I don't know. Here's the current setup.
The performance was flaccid and the single carb just looks wrong to me. But the thing started effortlessly which was good.
I picked up the 930 Premiers pretty cheap so I bit the bullet.
The new carbs come setup with - main jet 200, N - Jet is 106, Pilot 17 and Valve 3. I'm thinking it should have 220 mains.
The motor is fairly stock except for the Hepolite's which probably raise the C.R. a bit. So before I install them does anyone know if the jetting is in the right ballpark?
Going to be using a dual K+N filter. Should be similar to an early Commando right?
The bike had a single Concentric, which may be original to the bike, I don't know. Here's the current setup.
The performance was flaccid and the single carb just looks wrong to me. But the thing started effortlessly which was good.
I picked up the 930 Premiers pretty cheap so I bit the bullet.
The new carbs come setup with - main jet 200, N - Jet is 106, Pilot 17 and Valve 3. I'm thinking it should have 220 mains.
The motor is fairly stock except for the Hepolite's which probably raise the C.R. a bit. So before I install them does anyone know if the jetting is in the right ballpark?
Going to be using a dual K+N filter. Should be similar to an early Commando right?
mschmitz57 said:
Probably not, concentrics didn't appear until 1967.
mschmitz57 said:
Adding aircleaners alters the required jetting, but it does sound like Commando setup would be about right.
But K&N may not be quite the same, so you tell us...
If you don't ever give it full throttle, main jet settings can be tested out later.
For what it's worth, at one stage I had concentrics on my 650ss. The carbs were straight off a 750 Commando. It went very well straight away, I seem to remember fiddling about with jets, needles etc, because I felt that I should(!!). I cannot recall any major improvements with all the fiddling about.
Over time I tried most combinations, original Monoblocs, twin Commando Concentrics, single Monobloc, single Concentric. The single Concentric was probably the nicest to ride, especially in the Winter, but it didn't last long, it didn't look right, twin Concentrics definitely performed better.
Best of luck!!
cheers
wakeup
Over time I tried most combinations, original Monoblocs, twin Commando Concentrics, single Monobloc, single Concentric. The single Concentric was probably the nicest to ride, especially in the Winter, but it didn't last long, it didn't look right, twin Concentrics definitely performed better.
Best of luck!!
cheers
wakeup
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I started installing the dual Premiers on the Atlas today. I had to add a bit of clearance to the sides of the finned intake manifolds using a flat plate and some fine emery paper to allow them to fit side-by-side. Also had to remove a little material from the carb body where the unused idle adjustment bosses touch each other. So far I'm happy with the fit of the new hardware.
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Thanks. I've got a couple 220 main jets on the way.
Lowbrow Customs has excellent prices on these btw.
Lowbrow Customs has excellent prices on these btw.
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Finally rolled my Atlas out of the basement and fired it up on the 2 new 930 Amal Premiers. After some fiddling with needle heights I got it to settle down and run pretty well. My carbs came with float height around 1.5mm above the bowl. I'm thinking this may have been done by the guy I bought these Premiers from who fitted them to a BSA. I decided to leave them high since due to the angle of the carbs. Anyway, I'm thinking of dropping the bowels and lowering the float height (metal tang on stay-up floats). Does anyone have a recommendation on float height for Atlas engines?
As far as tuning goes, the pilot air adjust screw seems to function in the correct range (i.e. 1-1.5 turns out). Using 220 mains and 106 needle jets a whatever needle and slide comes with the 930 premiers.
As far as tuning goes, the pilot air adjust screw seems to function in the correct range (i.e. 1-1.5 turns out). Using 220 mains and 106 needle jets a whatever needle and slide comes with the 930 premiers.
