1965 650SS WHAT CARB(S)?

Option 4 have original bodies bored and slides sleeved and all new jets and needles. I use Kevin Traill for the machining and get the option vapour blasting. contaxct details

Alverstoke Restorations in Gosport, Hampshire. KJTRAILL@qinetiq.comTelephone: 02392 580708 (after 16:30).

Option 5. Twin concentrics, as per later 650ss.

I think it depends on your riding style and how important it is for you to keep it original.

A difficult one this! As it's a 650SS it's pretty much essential to have twin carbs or else it's not really an SS! For ease of riding though, a single carb would be easiest.

Does Kevin re-sleeve monoblocs? I'll send him an email. Thanks for the link.

My 1965 650SS was fitted with twin concentrics when I bought it, but I also had issues with the right hand running rich.

I eventually bought a single carb manifold from Norvil & fitted with one of the carbs.

Could not believe the way it ran with no alteration to jetting.

Just set tick over & did a plug test after running bike for a while.

Now smooth running with steady tick over & I can not see any difference in power.

Previously anthony_bolton wrote:

Dear Members,

I have a 1965 650SS owned by me since 1976 and equipped with the original whole Monobloc on the left and "chopped" Monobloc on the right. Both carbs are completely standard with regard to jetting, needle and throttle specifications. I've had a few carburation issues in recent months and poor starting i.e. right hand carb seeming to get more petrol than the left. All this has led me to think it is time to renew.

There are a number of alternatives:-

(1) Buy new Monoblocs as per original specification - one whole, one chopped.

(2) Buy two new handed Monoblocs

(3) Buy a single carb conversion kit and new Monobloc with appropriate jetting.

I'm interested in hearing the views of members particularly the pros and cons of Option 3?

Suggestions gratefully received.

Regards,

Peter Bolton

(2) Buy two new handed Monoblocs

Your option 2 may not be possible. The handed Monoblocs would interfere with each other. There is no room for both float bowls unless you get one of those splayed manifolds but that just wouldn't look right.

I might be missing something here, but my Altas had a pair of handed monoblocs (389s) before I changed to a single carb - a very worthwhile modification. So handed monoblocs should fit a 650SS.

Previously Gordon Johnston wrote:

I might be missing something here, but my Altas had a pair of handed monoblocs (389s) before I changed to a single carb - a very worthwhile modification. So handed monoblocs should fit a 650SS.

Here is a pair of handed monoblocs with adjustment screws out (the logical choice). I could not get them on the right studs but no matter.

and here is a pair of handed Monoblocs with floatbowls out (don't laugh). The throttle stop screws interfered so... not recommended.

Which of these 2 arrangements did you have, Gordon?

Now you're asking! The very first thing I did to the Atlas was fit the single carb manifold - from a Mercuryas it happens - and I didn't really take note. It was 25 years+ ago. It could only have been the second arrangement. Puzzling really as it only had short non-splayed single manifolds. I just used one of the carbs without any readjustments and it still works fine. If you want to see a really dismal carb setup, look at an early Series B Vincent twin. Throttle stop and pilot screw hard up against the cylinder head.

Previously Gordon Johnston wrote:

I might be missing something here, but my Altas had a pair of handed monoblocs (389s) before I changed to a single carb - a very worthwhile modification. So handed monoblocs should fit a 650SS.

It should be a twin carb with a shared float bowel.

Fritz

I've certainly seen the monobloc with acut-off float chamber set up on pre-downdraught heads.

I've only ever seen the cut-off style on all 650s and 750s other than single carb up to 1967. That's in the US. I saw very few Nortons in the UK and I wasn't paying attention in those days.

Previously anthony_bolton wrote:

â?I also bought a 2 into 1 manifold kit from Norvilâ?

Unfortunately this one has only the outer two bores to screw it on.I've made the two inner bores myself, using the heat insulators as templates.

Fritz

Previously anthony_bolton wrote:

but they're now in the hands of Kevin Traill for refurbishment, at least then I can convert back if I want to.

Kevin has refurbed a number of carbs for me ,his work is good, he is very concientious and knowlegable.

What did Kevin do to them, and dare I ask, what does he charge?

Hi Peter. That sounds quite fair. Considerably cheaper than replacing with new, in the knowledge that they have been checked and rebuilt by hand, whilst retaining the original carbs rather than consigning them to the back of a dusty shelf for ever.

Thanks for that info.

What condition are your mirror-image Monoblocs in? I'm interested to know if you discarded them because they were worn out, or because you disliked the installation.

Actually, I am interested in buying a pair of 1 1/8" Amal 389 / 689 carbs if they are in good nick

Paul

Previously Jonathan Soons wrote:

Previously Gordon Johnston wrote:

I might be missing something here, but my Altas had a pair of handed monoblocs (389s) before I changed to a single carb - a very worthwhile modification. So handed monoblocs should fit a 650SS.

Here is a pair of handed monoblocs with adjustment screws out (the logical choice). I could not get them on the right studs but no matter.

and here is a pair of handed Monoblocs with floatbowls out (don't laugh). The throttle stop screws interfered so... not recommended.

The 650ss had 276 carbs, chopped on the right. The mirror image Monobloc was never made for the 276, just the 389, in 1 1/8" and 1 5/32" sizes,

see: http://archives.jampot.dk/Technical/Carburation/Amal_Monobloc__numbers_type_and_use.pdf

Paul

Previously Jonathan Soons wrote:

I've only ever seen the cut-off style on all 650s and 750s other than single carb up to 1967. That's in the US. I saw very few Nortons in the UK and I wasn't paying attention in those days.