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650SS Air Slides/Choke

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I have rebuilt a 1963 650SS with two new Amal Monobloc 376 carbs with no air slides fitted. However, I can't start it.  It will fire occasionally and kick back but that's all.  I will recheck the timing. 

Were air slides/chokes fitted originally to twin carb models and will they help?

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Hello i have same problem on my commando someone takes out slides from karbs. and in winter i can not start my bike. only way was take fuel under sparks. now i take back slides and machine takes on second kick in winter.

on 650 ss i have carbs with slides and starts good.

but timing can makes this problems too.

here is schema of carb with choke slides

http://amalcarb.co.uk/carbspec/carburettor/spares/id/6775/

good luck

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Don't racers remove air slides because they are just one more thing to go wrong?  And one more thing to maintain.  They were certainly fitted originally so I wonder why you have left them off if the carbs are new.  if you don't have them - have you blocked the cable entry holes at the tops of the carbs?

If it won't start - are you sure you have flooded the float chamber?  All the books and magazines repeat the comment made by the road tester in 'Motorcycling' that the downdraft carbs are prone to flooding and this then makes starting a problem.  I've never found that to be true myself.  But I certainly use the air slides when it's cold,  but only for a very short time.

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When setting up a race bike, you remove all unnecessary parts to get it as light as possible. First you don't race in really cold weather. Second you warm up the engine before race to get oil flowing easily and to get correct carburation. If needed when cold you can get choking simply by partially masking air intake with your hand. The air slide on the GP carbs was mainly for fine tuning mixture depending on different air pressure and temperature. Most racers omitted them.

I do have them but was advised by someone that they weren't really necessary so I removed them and blocked the cable holes.

Yes, I have flooded the float chamber.  I've also tried easy start spray to no avail.

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hello this sounds like timing is out and may have been timed up wrongly  to do the timing you should all ways start from the drive side or left  side with the point turned up ward and the points cam at the bottom or coming too the bottom  then you find were the breaking point is on the points and have  the left hand piston at 32 degrees before top dead center  with your ATD on full advance  and points just breaking with your fag paper  try to keep all this still and do up the ATD bolt  and it would good if you can fit a pair of choke sides just to take up the space and stop too much air getting in the carbs making it run very weak,   hope this may shed a light on things  have fun yours anna j

In reply to by anna_jeannette_dixon

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Thanks Anna,

I am fitting the choke slides and will redo the timing. I have manual advance/retard

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Hello  Normally  The 650SS has Automatic  Timing device, So what Magneto have you has all 650ss  Had  the Lucas  Competition K2FC, Only the Delux 650 and Standard 650s  Had the  Coil-ignition   The Norton Manxman 650  right from November 7th 1960  had the Lucas K2FC  and their date stamped on each Magneto  to the Motor,  like my Norton Manxman 650 has the date stamp on the magneto 12/60   and with a manual advace and retard  lever as to be fully advanced  and all your timing is done from the left-hand side  with a timing disc  fixed well to the crank end  three bit of glue tack at the back of the timing disc  then fixed to the rotor  and do up the big nut,  hand tight  and fix a good pointer on the rear  barrel stud,  and take thing from there have fun and  good luck  yours   anna j   

In reply to by anna_jeannette_dixon

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It's a K2F with a cutout button on the end. Based on the box of bits I bought it's probably not the original!

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So Barry.....

How is the starting now that you have replaced the slides?

Mike

I haven't had time to do anything yet as I'm away. I'll report progress when I can.

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You need to make sure you have good sparks too, not just feeble ones. It should run without the choke slides but may of course need tickling a little while very cold. The mags can be rebuilt if required to restore the sparks.

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I am just getting my old 650SS ready to ride again. In so doing I sent the worn carbs for a refurb,  incuding fitting air slides which it has never had in the forty-one years I have owned the bike. Having purchased new cables through the club, and an air lever from elsewhere, I find,today, that the cables seem too short, as the air slides only reach about half way down their travel with the air lever closed. Does anybody know if there are air levers which wind on differing amounts of the cable when closed, as I imagine the cables (One from handlebar lever, splitting into two to the carbs) will be of a standard length?  The lever I purchased was described as a Doherty-pattern.

Thanks for any ideas in advance.

David Francis.

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Just a thought David - You did not say what version of carbs are fitted to your '66 650SS.  They could be 376 Monoblocs or 928 Concentrics or someone may have fitted 389 Monoblocs.  All of these options would have used the same twist grip, air lever and cable junction boxes but all the options have different air slides and unfortunately need different cable configurations between the junction block and the carb tops.  When I swapped my 376's to 389's the air slide only moved about half-way down the body.   Good luck, Howard  

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It does sound as though maybe the cables are for Concentrics, perhaps.

Howard, my 650SS has a single carb at present, but I have a pair of 1 3/16" 389's off a RE Constellation, which makes them about the same size as the later 930 Concentrics. What size are yours, and do they work satisfactorily? I was concerned they may be too much carb for that engine. Mine does not have inlet sleeves.

Ian

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Ian - On my road bike I settled with 1 1/8 inch monoblocs (one chopped float chamber) from an Atlas but on my racing bike I ran 1 3/16 inch paired 389/689 monoblocs.  930's are a bit large for a standard 650 unless you've got a Hemmings, or Fed Barlow, or Norman White or some such ported head.  Mine work fine with Curley camshaft, uprated valve springs, bronze guides, Commando valves and Dunstall head..........but I'd leave it on a single carb for everyday riding.  Cheers, Howard

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Howard. I would have also thought that a pair of 930's were a bit large, but Norton fitted them as standard from 1967-.

The single carb does run out of puff, though.

Ian

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Hello again - My brand new '69 Commando wore a pair of 930 Concentrics but it was good for another 10mph than my '66 650SS that had 1 1/16 inch Monoblocs and tin sleeves down the ports.  It was also a lot thirstier.........  Whatever size you employ it is important that the charge flows evenly into the cylinder so no steps in the carb/manifold/port track is important.  That's probably why the later Plumstead machines were no match for the earlier ones.  I expect AMC bought their carbs in bulk and were selling mostly export Atlas and Hybrid models so why not fit the same size to the few 650's being built ?  Some will say that's a cynical view but something slowed them down and it wasn't the twin coil set-up.  Ho hum, ride safe.  Howard

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Further to previous posts, I have been playing around with the cables, and both sections i.e. from handlebars to junction box, and from there to carbs and both outers are seemingly too long, or the inners too short by about half an inch or so. The pity is I bought them from the NOC. Maybe I got a duff set as I can't see any evidence of others with a similar problem. Does anyone know of alternative suppliers?

David Francis.

 

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David - The twin carb set-up on Dominators always employed adjusters at the carb tops unlike Triumph and BSA amongst others.  You haven't mentioned this so I am just reminding you that the Club will assume they are for that set-up unless you specify otherwise.  Half of an inch on the inner cable is soon lost with the adjusters on the carb tops.  JJ Cables is where I prefer to buy all my cables but you will need to specify exactly what you require.   Good luck, Howard 

 

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