Atlas single carb conversion

On my Rally touring Atlas I fitted a single 930 Concentric. This worked well for me, giving 60+ mpg when motorway cruising. I did try a 932 which restored the acceleration oomph and top end that I lost with the single 930 but it guzzled fuel and idling was always lumpy. RGM used to offer a complete single carb conversion. You got a manifold and choice of carb.

See attachment for their advice page.

I should have a single carb manifold on the shelf. I'll pop out (through the snow) and check shortly.

@Gordon

Have a look here http://www.norvilmotorcycle.co.uk/carbmanif.htmand here http://www.mapcycle.com

Fritz

Paul. If you don't want to splash out on a new carb at the moment, one of your monoblocs should go straight on the single carb manifold, without touching the settings, as a starting point. Unless they are kn#cked, that is! Failing that, if you go the concentric route, I may be interested in your monoblocs..... Unless they are kn#ckered, that is!

Ian

Hello Gordon

Have a look here (Holland

http://www.deengelse.com/

http://www.deengelse.com/specialdomicarb.htm

RenÃ?

Paul - Should you choose to go with a single carb try to get the manifold that secures to the head with two studs (outer fixing) and two cap-headed allen bolts (accessed through the carb orifice). I got one that only fixes on the two outer studs and it continually leaked air to the inlet. I got it machined to fix the fault - not cheap. All the Mercury models had the better manifold. Some people claim Genuine Norton part - but beware. Good Luck, Howard

Previously howard_robinson wrote:

Paul - Should you choose to go with a single carb try to get the manifold that secures to the head with two studs (outer fixing) and two cap-headed allen bolts (accessed through the carb orifice). I got one that only fixes on the two outer studs and it continually leaked air to the inlet. I got it machined to fix the fault - not cheap. All the Mercury models had the better manifold. Some people claim Genuine Norton part - but beware. Good Luck, Howard

Look up 'MotoCarb' and if using the four point fixing manifold don't forget the Loctite on the inner fixings.

Mark.

Previously paul_dudill wrote:

Thank you to all that replied with most useful advice. Gordon has come up trumps with the manifold and I will update once it's fitted with a 389, hopefully I can put some miles on it this year! Paul.

I recently fitted a NORVIL single carb manifold to my 650SS using one or the original carbs.

Spot on with next to no setting up required.

I wouldn't think one 1 1/16" carburettor is big enough for a 650SS

Previously thomas_newton wrote:

Previously paul_dudill wrote:

Thank you to all that replied with most useful advice. Gordon has come up trumps with the manifold and I will update once it's fitted with a 389, hopefully I can put some miles on it this year! Paul.

I recently fitted a NORVIL single carb manifold to my 650SS using one or the original carbs.

Spot on with next to no setting up required.

Previously paul_standeven wrote:

I wouldn't think one 1 1/16" carburettor is big enough for a 650SS

Previously paul_dudill wrote:

....once it's fitted with a 389...

Paul S..... 389 Monoblocs start at 1 1/8".....

Having said that, Triumphs used to fit small carbs. For example, T110's from 1955-61 were fitted with a single 1 1/16" 376, and they went rather well.....

Hello Paul.

Can you tell me what you use for adjustment?

Throttle Slide?

Needle Jet?

Main Jet?

Thanks in advance.

RenÃ?

Also a simple fix for the problem of fuel overheating and vapourising that was a constant pain on my Atlas when trying to use the bike for stop/start work. The extra flow through the single carb setup keeps the fuel cooler. Much better economy too. However, had to dress the mating surface on the manifold on a sheet of plate glass to achieve a seal between the manifold and the head.....gasket notwithstanding. This was a new part from one of the usual suspects. Disappointing.

David Chambers

Previously rene_evers wrote:

Hello Paul.

Can you tell me what you use for adjustment?

Throttle Slide?

Needle Jet?

Main Jet?

Thanks in advance.

RenÃ?

----------------------------

I set my single cab Atlas up with similar settings to those used on the single 930 Concentric carb Mercury 650.

so......280 main jet

.........106 needle jet

.........throttle valve 3

.........pilot jet 25

These worked well for my engine with no air filter. The plugs were the right colour, the bike started easily and gave up to 60mpg when cruising at 70mph.

Thank you very much Phil

Regards RenÃ?

My single carb Atlas is running on the standard 389 book settings:

main 350, needle 106, pilot 20, throttle slide 3, needle D on position 3.

I just took one of its twin carbs when I did the change and didn't alter it in any way.

It goes rather well and gives about 60 mpg.