Atlas single carb manifold conversion

Possibly  a Mercury one, or one from  an early Atlas.  We have an  after market  one but have  machined it for  4  allen screws .

They have two visible bolts on the outer edges, and two Allen screws inside. Use loctite on the Allen screws. They are in the air/fuel blast and you do not one in your inlet valve. I had a lucky escape once when I had only the one carb on my 88SS.  (Why do screws vibrate out and not vibrate in? Perhaps they behave the opposite way in Australia?)

I still don't see the point of making the change but that's a topic that's been done to death in the past.

The arrival of the 650 cylinder head enabled the mounting of twin carburettors straight onto the horizontal flanges at the back of it. For those who wanted to keep a single carburettor a 2 into 1 manifold p/n 23357 was available. This part was revived for use on the 650 Mercury in 1968.

The 23357 manifold had 4 holes to mount it on the SS head and  as Dave mentions, using nuts/bolts on the outer holes and Allens Bolt on the inner 2.

By the late 1970s Norton Twin owners began asking for conversion kits to get round the issue of re-tuning twin carbs every month. Enter Stewart Engineering who started offering manifold and carb for a tidy sum of cash. Instead of 23357, on the outside of the manifold, the word Stewart could be found. 20 years down the line and other noteable Norton parts/spares providers jumped onto a growing market and began supplying similar conversion kits. The big difference being a modification reducing the 4 mounting holes to 2. Thus probably getting round 'copyright' issues.

This neat solution for the suppliers led to a big problem for the buyers who suddenly discovered that any carb to head heat insulators would no longer stay in situ due to the 2 missing studs. I got round this problem, on my 750, by fabricating 2 dummy studs mounted on the head and drilling the manifold to accept the stud tips. See attachment.

Here’s an image of the Stewart Developments single carb manifold on my ‘68 Atlas

cheers

Simon

When I fitted a Mercury manifold to my Atlas, I just used one of the carbs with no changes whatsoever and it has been absolutely fine. It does mean I have a complete spare carb ready to go sitting in the drawer.

Hi Simon....thanks for posting the photo. I note locknuts on all the manifold studs. Does that mean those studs were UNF threads? Plus is your manifold held by 2 or 4 studs?