Twin carbs internal manifold balance pipe

Can't emphasise enough - tuning to get more power form a 99 is a very short-term exercise. I have the shattered remains of crankcases to prove it. The previous owner went the single carb route for good reasons.

When my 99 was on twin carbs and an SS head, I didn't use balance pipes. It was smooth enough and the tickover was fine. Setting up the carbs and keeping them in balance was a bit tedious, which is why I went back to a single carb.

Hello I am with John One this one and I am a Engineer .I have the 650 Manxman they had the first down draft cylinder head Now they Call it a SS head But it should be a Manxman cylinder head and its same with the high lift camshaft and flat followers they had them well before the 650SS . anyway I have the twin carb and fitting for it ,,,But I fitted a Single Carb and I can still get over 110 mph if I wanted too , but 80mph is fast enough for me in our days on open road with No traffic around , going too fast you only end up hitting something hard like the road or a brick wall or a tractor or car. and then is game over. yours anna j

Previously steve_marshall wrote:

Well there is a clear consensus that 99SS's were fiddly to synchronise with their original twin carbs. I want to put the twin carbs back only for the purposes of orginality. 80mph is quick enough for me too.As Norton, BSA and Triumph added small-bore balance pipes to all of their 70's twins and triples (AFAIK) as a measure taken with the intent of mitigating this problem, it looks like it would at least be worth a try.Taking into account that it will be completely invisible and easily reversible. I think I will give it a go.Steve

My 99SS came from the factory with twin monoblocs as per specification and went well. Twin carbies are fine until you start to get some wear. I have the twin monoblocs back on it but prefer to ride my 650SS which I converted to a single concentric. Much simpler and don't really notice any difference in acceleration. Can't use the top speed here on Oz due to speed cameras propagating like mushhrooms in Autumn.

Very true Gordon. For anyone interested in tuning or just rebuilding a Dominator, I have received an e-mail from Steve Campbell of Thunder Engineering that they have manufactured the next batch of Dommie con rods at £250.00. As they are known to be a weak spot I will be replacing my 54 year old rods during my full strip down.

stevecampbell@thunderengineering.co.uk

Previously gordon_johnston wrote:

Can't emphasise enough - tuning to get more power form a 99 is a very short-term exercise. I have the shattered remains of crankcases to prove it. The previous owner went the single carb route for good reasons.

Previously steve_marshall wrote:

I am rebuilding a 99SS engine which was converted to single carb and concentric by some sensible owner in antiquity.

I am less sensible and I have acquired twin monoblocs and an original manifold.

I was considering drilling a couple of internal 3/16" holes diagonally to 'share' the carbs on tickover/low throttle opening to ease with balancing. Has anybody tried this or have any views on it?

Steve

I have a 650ss with new monoblocs and i had to fit a ballance pipe to the inlet manifolds to get a smooth even tick over.paul Wolf

Previously steve_marshall wrote:

Well there is a clear consensus that 99SS's were fiddly to synchronise with their original twin carbs. I want to put the twin carbs back only for the purposes of orginality. 80mph is quick enough for me too.As Norton, BSA and Triumph added small-bore balance pipes to all of their 70's twins and triples (AFAIK) as a measure taken with the intent of mitigating this problem, it looks like it would at least be worth a try.Taking into account that it will be completely invisible and easily reversible. I think I will give it a go.Steve

Hello to fit twin carburettors you need two new carbs as its no good trying to balance old worn carbs , it just will not work. you need new Amal 376/288 and 376/289 and with this ethernol you may have to go down a size with the main jet to a 240 or even a 230 main jet but the standard jets were 250 , 25 pilot 106 needle middle notch No3 the notch start at the top , with No1 notch the 99ss had a spladed inlet manufold these are available that RGM Motors and so are the twin cables too . hope this helps

Previously anna_jeannette_dixon wrote:

Previously steve_marshall wrote:

Well there is a clear consensus that 99SS's were fiddly to synchronise with their original twin carbs. I want to put the twin carbs back only for the purposes of orginality. 80mph is quick enough for me too.As Norton, BSA and Triumph added small-bore balance pipes to all of their 70's twins and triples (AFAIK) as a measure taken with the intent of mitigating this problem, it looks like it would at least be worth a try.Taking into account that it will be completely invisible and easily reversible. I think I will give it a go.Steve

Hello to fit twin carburettors you need two new carbs as its no good trying to balance old worn carbs , it just will not work. you need new Amal 376/288 and 376/289 and with this ethernol you may have to go down a size with the main jet to a 240 or even a 230 main jet but the standard jets were 250 , 25 pilot 106 needle middle notch No3 the notch start at the top , with No1 notch the 99ss had a spladed inlet manufold these are available that RGM Motors and so are the twin cables too . hope this helps .Ps the 99ss did not have inlet balance pipes , I had a 99SS yours Anna J

Previously steve_marshall wrote:

I am rebuilding a 99SS engine which was converted to single carb and concentric by some sensible owner in antiquity.

I am less sensible and I have acquired twin monoblocs and an original manifold.

I was considering drilling a couple of internal 3/16" holes diagonally to 'share' the carbs on tickover/low throttle opening to ease with balancing. Has anybody tried this or have any views on it?

Steve

Hello The Model 99SS did not have the down draft cylinder head until very late on . only the last ones . so they had the spladed inlet manifold , with out balance pipes ,

Previously steve_marshall wrote:

Hi Anna

Well I was going to give it a try with some antique monoblocs, which is one of the reasons I thought that balance pipes might be a help. They are in pretty good shape though, and only 50 years old, plenty of lif0e left in them.

I have the original, rather agricultural, Norton 99SS splayed 'adaptor' manifold. PS the RGM items are sized for 88SS's, though I imagine no big problem opening them up a little. My head is not downdraught.

Norton and Triumph twins had quite a long balance pipe route, and I think that the connections might have been intended to be used for balancing with a manometer. Balance them, then connect them together. The triples went a different route with short bores interconnecting each cylinder's inlet tract with the other two via cast-in bores in the carburettor gantry.

Steve

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Hello with balance pipe in your case would not make it any easer to balance . the way to balance your carburettors is first you need find out how much fuel is in each carburettor . and get this on a balance first . then start with taking out the right hand spark plug. and start your engine on the left hand side cylinder and get this cylinder running right and have a nice tick over then do the same with the right hand cylinder. then both cylinders they rev like hell at first but tweaking the left hand one first then the right hand side last . The left hand side cylinder is the Drive side cylinder so we alway start with this cylinder first. even when timing the motor . On a Magneto model the Drive side plug lead will be the lead nearest the battery box . the right hand lead nearest the back of the cylinder barrel and its the same with a Distributor and the coil should be mounted on the left hand side head steady nearest the front of the tank with the lead facing back to the seat and into the distributor this is how my (99SS) was set up . and it was a very fast (99SS) there was not much in the difference between the (99SS) and The 650SS a good 99SS will give your 650ss a good run for its money ,there a real good motorcycle and I wish I still had my one 633 WF hope your out there somewhere yours anna j