389/689 on a 650SS?

Previously wrote:

Hey everyone finally done a bit more work on my norton

just got the single carb conversion off of her and was thinking Ive got one minty fresh 389 and was wondering fitting the matching opposed float bowl 689 if I can find one

Anyone ever fitted that setup on the 650ss. Bit worried a bout the idle screws hitting each other ?

Without the metal inserts the actual manifold bit bore is spot on to the 389

Thanks in advance,

Tom

Hello Tom - What are you going on about! The 650SS had 376/288 Lh and 276/289Rhwith this ethanol in the Petrol I would try and fit a main jet number 240 ,with a 3.1/2 cutaway throttle sided and needle in position 3 grove see if this helps . but the single carb its Ok for the traffic in our days as its slower that ever before .with all these speed cambers all over the place, yours Anna j

Hello Tom - computer error - its on the blink again! Amal Carburettor Numbers you need are 376.288 LH & 376.289RH. This one is a chopped Monobloc - they link up with banjos under each carb and you will need the spacers but do not go for the finned ones you need the ones with balance pipes underneath each one, these were the right set-up for 650ss. your Anna j

If you want to use the bigger carb - dimensions are on the Amal web site.

(Do they now sell LH and RH? The original had the smaller body (376) 1 +1/16" with one missing float didn't it?)

http://www.amalcarb.co.uk/documentdownload.aspx?documentid=39

This is a 'pdf' - although it doesn't say it is...

Previously wrote:

If you want to use the bigger carb - dimensions are on the Amal web site.

(Do they now sell LH and RH? The original had the smaller body (376) 1 +1/16" with one missing float didn't it?)

http://www.amalcarb.co.uk/documentdownload.aspx?documentid=39

This is a 'pdf' - although it doesn't say it is...

Hello its all very well to use 398and 698 handed carbs but they will need jetting right the main jet would have to be a 240 main jet a size 3.1/2 cuter way or a size 4 if needed a size 4 makes the motor run leaner or you could try dropping the needle one notch if needed you just have to get the motor running with out any black smoke my uncle Freddie us to tune his bikes and car with the exhaust pipes off so he could see the blue flame pattens just like a jet engine you look for the blue diamond patten in the flame but on the four stroke you look for the darker blue on the outer edges and a light blue in the middle and it should look like half a diamond patten as it flashes out ward ,or get your self some colour tune plugs yours AJD

Norton put the right and left handed Amal monobloc onto the 1966 Atlas right at the factory. It would be easy to look up the specs for the carbs in some of the popular books on Norton motorcycles, like Bacon etc..

Tom seems to want to use the bigger carb so he'll need settings not in the book.

In this month's Roadholder there is a letter about the 650SS input tracts. Made for 1+1/8" carbs but then sleeved down at the factory (just like 88SS) to 1+1/16". I've read somewhere (probably Bacon's Norton Twins but I can't remember now) the large carb was too big for road bikes and the bikes went better with road cams with the smaller carbs. Maybe the works left the duct alone a) because they'd made lots of heads before they worked this out and b) maybe they recognised it was then easier for amateur racers to uprate their engines. And of course c) they didn't want to re-tool.

I have the left and right handed 389/689 set up on my 650ss engine. It has a 99 head with a splayed fabricated steel manifold that I don't know the origins of. (By the way I'm in the market for a 650ss head if anyone has one which isn't silly money).

The 689 is not available new. Of course most of the parts are common with its mirror image buddy, but if you wanted a handed part, a slide for example, it would be a matter of finding new old stock.

I have my carbs stripped down at the moment, so ask if you want to know the jet sizes I have been running with.

Aren't there conflicting stories about whether the later heads were all that much better than the earlier ones? I once met one of the earlier 88SS bikes - one with the early head design - on the road when I was on mine with the usual later head (same as 650SS) and his was a lot quicker than mine! Annoyingly! (although I'm sure i have the wrong camshaft)

Any motorcycle will need fine tuning, jetting etc. to get the best of it, but the Atlas specs for the 389 would be a good place to start and I am sure would be very close.

The late 650ss used the 30mm Concentric carbs without any inlet sleeves and ran just fine with that setup.

The Norton works had very little money for development, especially after AMC got hold of them. In a financial position like that I doubt if they would have spent the time and money on developing new cylinder heads for no reason at all. Comparing two questionably tuned bikes on the road means nothing, for instance I once out-ran a dual-carb, splayed-head Triumph Bonneville with a single-carb TR6 in a contest of 100mph speeds, both machines rebuilt to factory specs, which means nothing more than the Tr6 was tuned much better, or there was something amiss with the Bonneville's engine.....

Previously wrote:

Any motorcycle will need fine tuning, jetting etc. to get the best of it, but the Atlas specs for the 389 would be a good place to start and I am sure would be very close.

The late 650ss used the 30mm Concentric carbs without any inlet sleeves and ran just fine with that setup.

The Norton works had very little money for development, especially after AMC got hold of them. In a financial position like that I doubt if they would have spent the time and money on developing new cylinder heads for no reason at all. Comparing two questionably tuned bikes on the road means nothing, for instance I once out-ran a dual-carb, splayed-head Triumph Bonneville with a single-carb TR6 in a contest of 100mph speeds, both machines rebuilt to factory specs, which means nothing more than the Tr6 was tuned much better, or there was something amiss with the Bonneville's engine.....

Hello Ben - Yes I can agree with that statement there was something amiss with the Bonneville engine. It's called overheating ,

Yours Anna J