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Posted By: Ianbuck A65 Carb Question - 01/29/19 12:32 am
I've got a few jobs left before I can have a go at starting my A65. My current focus is on the caburettors. The bike was standing for +20 years before I got it, however new carbs were fitted some time before it was put into storage.

The bike is a 1970 A65 Lightling and the carbs are Mk1 Concentric 300/930's with 200 main jets. The throttle slides are 928 No3, and the needle clips are set in the top slot.

I know I will need to spend a bit of time tuning them when the bike is up and running.

My questions are:-

Are these carb settings what you would expect with a standard 1970 Lightning set up ?

I have fitted a new Siamese exhaust system with a standard clubman silencer.

Are the settings going to be OK to get me going with the Siamese pipes ?

What would happen if I change the original paper filters for velocity stacks or Amal filters. Will I need to change the jets and slides ?

Posted By: leon bee Re: A65 Carb Question - 01/29/19 1:28 am
Messing around with too lean can turn some new pipes blue quick. As in MY new pipes. I didn't really care, they were cheap aftermarket, but some folks might care.
Posted By: Allan G Re: A65 Carb Question - 01/29/19 1:38 pm
From my own experience,

depending on whos clubman silencer you have will determine the jetting, armours are quite restrictive. I had a wassel (I beleive) on mine and found it worked with the standard jetting (only thing I had to do was sleeve the tail pipe as there was too little back pressure, causing me to keep the bike higher in the rev band)

stock 1969/70 jetting was #3 slide, needle groove in top position (position1) 106 needle jet and a 180 main jet!

If you change to stacks you will need to change everything..... Notice I say velocity stacks and not belmouths. The stacks isolate the idle mixture, bellmouths usually just need a bigger main jet!

For the stacks I found

#3.5 slide
105 needle jet
needle position in the middle groove (pos 2)
250 main jet

It also helped retarding the ignition to 31 degrees, at WOT the 250main (with 34* advance) will run faster than the 240 mains, but it will "8 stroke", retarding the ignition cured this, I never tried a 260 main to see if it improved further!

What also helped was setting tappets to .010" for inlet and exhaust, it changes the cam timing slightly. It seemed enough to give the bike more torque.

Whos downpipes do you have? most are poorly made and not good for gas flow of the left pipe into the main. check the short pipe enters the main pipe with no obstruction. Not checking this caused damage to my cylinder! (gas not escaping properly). The original factory pipes were a true siamese and the adjoing pipe met the right hand pipe over a long section. my copy is like this and works brilliantly!!

exhaust section on my resto thread
Posted By: Ianbuck Re: A65 Carb Question - 01/29/19 2:40 pm
My engine is dated April 1970, I've not had it apart so I can't confirm it's factory spec inside.

From the Haynes manual the carbs I have look like May 1971 Lighting spec, these have the larger 200 main jets, with the needle potion set at 1, and throttle valve 3.

As I'm going for a clubman (Cafè) trim I quite like the look of the Amal filters. I assume these would be OK with the Siamese pipes, perhaps ballence the richer exhaust system ?

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Posted By: Ianbuck Re: A65 Carb Question - 01/29/19 3:02 pm
Thanks for your reply Allan, I was typing when yours must have arrived. I've recently set the tappets to 8 and 10, I'll reset the inlet to 10.

I the junction of the pipes was quite good, but I did a bit of work on it with a long file, so it must be as good as I can get it now. Picture is before my filing.

I have a colour tune plug so I should be able to check the mixture with that when I get it running. And of course keep an eye on the actual plug colour.

In the past I've been quite good with carb ballencing on older cars and recently with modern 4 cylinder bikes. I've also got a air flow measuring gauge somewhere in the garage, that I used on SU carbs.


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Posted By: gavin eisler Re: A65 Carb Question - 01/29/19 8:16 pm
Stick with the original filters , they keep some of the rain out unlike the bolt on types. Originally the 1970 had a balance pipe exhaust, I imagine the stock settings will get you close, but it might possibly benefit from slides with leaner cutaways, 3.5s. if you dont mind experimenting, if you go leaner cutaway and you get no spit back in the first 1/8th of throttle its generally a better running beast. If the slides are too rich the bike will accelerate well, but fluff/ hunt and stutter on a steady low when you are sticking to 30 in town, most annoying.
my 1970 factory manual says 190 MJs. maybe have 180s and 170s to try as well..if the siamese tends to run rich.

modern fuel is weird, it may be the book settings wouldnt be much good anyway,

Theres a lot to be said for a well tuned idle circuit,
Starting with decent cables, if you make your own , and who doesnt nowadays, then make sure the cut ends are ground dead square so there is no possible spring compression or tilt before fitting the end ferrules, nylon/ teflon lined cables are a V good idea, make sure to podger out the ground end with a hot needle to clear the heated liner, dont use the smallest outers, use the next size up, but use the smallest inners.

Empty the float bowls into an aerosol lid, just in case some water or muck is in there. there always is.

clean both pilot jets with a 78 drill ( you must get one or you are wasting your time on the rest of this set up, yes , even if its a new carb ),generous slack in the throttle cables 2-3 mm.
set pilot air mix screws about 1.25 turns out ( if starting from scratch).
then disco one side of the inlet balance pipe and plug the open ends ( I have tried to do this with the balance pipe connected and got very poor and confusing results, the dead cylinder feeds the live one and messes up the individual circuit),
i get best results from doing each cylinder individually for idle , after a 6 mile run ( take one plug out),
set the live pot to a 1,000 rpm idle and tweak pilot air screw to max revs, reset stop, and slightly richen mix screw about an 1/8th, drop revs to 800
,repeat for opposite cylinder ,reconnect balance pipe and fit both plugs, restart , idle will now be too high , drop each throttle screw an equal amount to desired idle ( around 900 -1,000),

then and only then synch the cables so that both slides lift exactly at the same time( air filters off to observe / feel slides), you can fine tune this with a balance meter if you have one.

This gives the cleanest pickup. for me anyway. I use a "ballometer " balancer, you can mount it to the bars and observe balance through the range, generally it reads perfect after a 1/4 throttle no matter how out of synch the cables are, but, getting the first 1/4 right makes a huge difference to driveablity. This took longer to type than do .

Tools needed,Gloves for hot plugs , one carb screwdriver, cable adjuster spanners, spark plug spanner, balancer if you have one.working tacho.
I have also tried drill rod synching, good to get you going but not perfect. And synching with just a balancer, doing this was OK, better than the drill rods , still not as clean as the 6 mile ride one pot drop technique.Cylinders are seldom perfectly matched, same goes for carb machining,using drill rods does not take into account either of these variables, a good starting point but not the end. T bolt owners dont kno what they are missing.and will be laughing up their sleeves.
Posted By: Ianbuck Re: A65 Carb Question - 01/30/19 3:40 pm
Some great info there Gavin ... Thanks. 👍 I've printed it off along with Allen's post for future reference.

I've given the carbs a good clean out with compressed air, they are like new with no visable wear. I'll order a few smaller main jets and some new floats, for now.

I found my old carb ballencing meters I'll use these prior to 'one pot' road testing as you describe.

I currently have a single throttle cable into a splitter. My carbs do not have cable adjusters on the top cover, I have cable adjusters on the single cable and on the 2 cables to the carbs.

Because the new tank I've ordered is the deep sided Spitfire modle, access to the adjusters under the tank may be a bit awkward?

My latest questions are:-

Will it be an advantage to change to 2 single cables from a new 2 cable throttle? The adjusters then being close to the handle bars ?

Will I also need adjusters on top of the carbs?

What does the 1970 manual say regarding the stock throttle needle postion ?

Thanks for your help.


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Posted By: kommando Re: A65 Carb Question - 01/30/19 4:27 pm
I've given the carbs a good clean out with compressed air, they are like new with no visable wear.

A word of caution, your pilot bush will be hidden under the pilot mixture screw, the only way to clean that reliably is to use a 16 thou drill held in a WD40 red tube, air and carb cleaner will not do the job. Even if its clear now it will get clogged by the ethanol in today's fuels, symptoms are non starting from cold with dry plugs despite tickling the carb and if you can get it started the throttle has to be at least 1/4 open, the idle speed will not be affected by the pilot mixture screw is another clue.
Posted By: Ianbuck Re: A65 Carb Question - 01/30/19 5:40 pm
Thanks Kommando I'll order a few of those drills, the carbs have been standing unused for over 20 years !! Do you have any recomendations for a good engineering suppliers for these small drills.? Obviously they need to be made accurately.

Posted By: gunner Re: A65 Carb Question - 01/30/19 6:04 pm
You can get 0.4mm micro drill bits easily enough on ebay, this metric equivalent is ever so slightly smaller than the #78 size (0.4 vs 0.4064mm) but cheap enough and usually available in packs of 10 for just a couple of pounds, see This link

Regarding the throttle cables, I'm using a twin pull twist grip and dual cables which I'm led to believe allows for more accuracy when balancing the slides. Currently I'm relying on the carb top adjusters to manage the cable slack but will probably migrate to making my own cables with built in adjusters below the throttle.
Posted By: Ianbuck Re: A65 Carb Question - 01/30/19 8:18 pm
I need new cables so the only extra cost would be the twin throttle. Amal do a nice looking period throttle.

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Posted By: gunner Re: A65 Carb Question - 01/30/19 8:53 pm
I'm using a similar twin pull throttle which I think is made by amal.

One thing to watch out for is throttle cablles which may be slightly too long or short overall and have an incorrect inner cable free length. I seem to remember my ones had an inner cable slightly too long which used up most of the adjustment on the carb top adjusters and left the throttle with a bit more free play in the cables than I wanted.

My next plan is to make up some new throttle cables possibly using a Venhill kit which includes a nylon lined cable and inline adjusters.
Posted By: gavin eisler Re: A65 Carb Question - 01/30/19 9:17 pm
A twin pull throttle is a very good thing, I fitted a single pull junction box type in 1983 and took it off in 1985, it was pish. my bike came with a Tomasselli 2C Daytona twistgrip, it has a larger radius drum than the Amal , doesnt need a double handful, has a stroke limiter to stop you pulling the ends of the cables . has a useful friction brake, handy for cold mornings. and has a neat waterproof flap for the entries. Its a solid lump as well , more crashtastic than the Amal An excellent bit of kit. You can still get them from Disco Volante,

You dont need or want carb top adjusters, put the adjusters about 6 " down from the bars for ease of access. Consider fitting swept bends at the carb cable entries, this is the nasty bend in the stock set up, carb top adjusters make this even worse, Venhills have all that stuff. If your carb tops are threaded for adjusters you can lightly drill out the threads to the size of the swept bend or cable ferrule. I use Mountain bike back brake cable "noodles", they are super skinny and plastic lined , gives a V light throttle, now the only outer cable bend is the large radius from headstock to throttle . You can save 90 £ on Vs birds nest tool , if you have a vice, drill press and some 2" angle iron and a dremel . Put that towards the cables and you have actually come out on top. A cheap soldering pot from China costs a tenner on the slow boat, Bakers Soldering fluid , and some solder, Sall you need.

You old carbs will work fine once the pilots are cleaned with the 78 drill, to keep this brilliant tool, get a small plastic coffin, the type individual reamers come in , make that the drill box and tuck it under the battery strap, otherwise it will vanish. Chronos engineering supplies have all that sort of stuff. On this page , 75 p each , buy a few, store one in the coffin and lose the rest. Go to their webshop and search " Wire Gauge Drill Number 78 (Ref: ND78)"

On old carbs its a good idea to buy two replacement Welch plugs from Amal.
Remove the old plugs , located in the roof of the float chamber, drill a small hole in the centre of the plug, drive in a suitable self tapping screw and waggle the old plug out, what you should see is a clean round hole/ chamber with two holes both small, one wee- er than the other , these are the pilot delivery drillings to the ventturi, entering this chamber at right angles is the pilot air adjuster drilling / jet passage, if you poke the 78 drill in the adjuster screw hole it should emerge in the exposed chamber. What you will almost certainly find is all the crud of ages, some of it rammed in by blowing through the air passage, clean it all out , refix the new Welch plugs and be happy you did. The two drilled holes from the Pilot mix chamber to the venturi are not as small as the pilot air jet, one is around 20 thou I forget what the other is 18 maybe, The 78 drill ( 0.0155", 15 1/2 thou) should waggle freely in these, they are sometimes partially blocked with oxides/ gum.
Posted By: Ianbuck Re: A65 Carb Question - 01/30/19 11:05 pm
I like the look of that Tomasselli throttle and it's about the same price as the Amal when you add in the cost of grips.

My carbs don't have threaded caps for adjusters and I agree the cables would benefit from a nice swept entry. I'll have a look at Venhills on-line catalogue tomorrow.

My carbs are like NOS, I think they were fitted new just before the bike was put in storage. I cleaned the outsider with a bit of autosolve, didn't take very long. There was a small amount of micro rusty dust in the botton of the float bowl but that was it !!

I have not cleaned inside the carbs apart from a light blow out with air. They look like new inside.

I'll buy some drills and a selection of jets for future tuning.

The next task will be setting up the ignition, a Boyer 3 unit is fitted. I will test the strength of the magnets first and start a new post on ignition in due course.

Thanks for taking the time to post all this info.


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Posted By: kevin Re: A65 Carb Question - 01/31/19 12:50 am
Originally Posted by Ianbuck

I have a colour tune plug so I should be able to check the mixture with that when I get it running. And of course keep an eye on the actual plug colour.

^^^this is excellent, but remember it only gives you idle settings and maybe throttle cutaway, if you're gentle.

run it WFO and you'll likely blow the mica out of the plug pretty quick.
Posted By: gavin eisler Re: A65 Carb Question - 01/31/19 1:26 am
Thee carbs do look pretty fresh, . On the road carb tuning is a lot easier with chokes fitted, if leanness is suspect at certain throttle openings applying the choke will give useful info. Cold starts are a lot easier as well, . If the idle mix is correct for hot running then starting without chokes will give poor cold running after the initial tickle runs out, if your bike runs well from cold with no chokes it will be too rich when up to temp, probably foul plugs and have high fuel consumption.
Posted By: kommando Re: A65 Carb Question - 01/31/19 7:35 am
The other design fault of the concentric is the same material is used for both body and slide, this causes rapid wear, so include new anodised slides in your shopping list and this will preserve the bodies.
Posted By: Allan G Re: A65 Carb Question - 01/31/19 1:27 pm
Originally Posted by gavin eisler
Thee carbs do look pretty fresh, . On the road carb tuning is a lot easier with chokes fitted, if leanness is suspect at certain throttle openings applying the choke will give useful info.

+1, always fit chokes to mine, sometimes you think a bike is running ok at WOT, you can close the chokes down and find the engine smooth out in revs a little yet not impeed performance..... Thats a darn good indicator for knowing your too lean.

Originally Posted by gavin eisler

If your bike runs well from cold with no chokes it will be too rich when up to temp.

More so with temperatures at the moment, its around -5* at 9am this morning. Whats it like around Argyll?
Posted By: gavin eisler Re: A65 Carb Question - 01/31/19 1:51 pm
Argyll is a sub tropical paradise, apart from the snow and the salt on the roads the palm trees are waving in an azure sky. Its freezin, my burst oil barrel is frozen over, good fettling weather. My bike is in a warm room keeping the Myford company getting a front end ectomy at the mo.

Back to carbs , in the UK Surrey cycles are good people to deal with, they tend to have stuff on the shelves that Amal dont. Good stuff like chrome brass slides. Very good to chat with on the phone.

The carbs in the pic, what sort of float needles are fitted, ? original plastic, ( hard to seat sometimes), Brass with Viton tips ( heavy , does weird things to float height, ) , or Aloominium viton, tipped ( current flavour of the month, seal well with no weight penalty).
I like the Al type. Ditched the brass ones 5 years ago, ditched the plastic ones in 1982..

The old floats are probably fine, I still have that type fitted with no issues using todays fuel, the stay up type replace a poor batch of floats made with bad glue that dissolves , older carb floats are OK. At some point Amal changed the glue for the plastic float to a "safer " type that fails with modern fuel, hence the Stay up float, it doesnt dissolve.
Posted By: Ianbuck Re: A65 Carb Question - 01/31/19 10:58 pm
God I love this Forum .... So much info available. I'm currently having internet issues so sorry for delayed response.

The original float needles are a brass colour with a black synthetic tip (left in the photo) the replacement ethanol resistant needle I bought look identical (right needle in the photo).

Posted By: Ianbuck Re: A65 Carb Question - 01/31/19 11:16 pm
Sorry I'm have internet problems again, can't upload photos, I'll try and send a meaningful post tomorrow.

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Posted By: koan58 Re: A65 Carb Question - 02/01/19 12:07 am
I think they are identical.
The alloy ones with the viton tip are what you should get. The brass ones cause difficulties with setting fuel level.
Don't waste time tuning with the brass ones in concentric carbs.
Posted By: Ianbuck Re: A65 Carb Question - 02/01/19 9:46 pm
Just a quick update.

I do have choke slides with these carbs, just need a to find a good place to fit a seperate lever, there's not much room on the ace bars with the Doherty 200 levers.

I ordered; the Tomasselli 2C Daytona twistgrip, plus some Alloy float needle valves, spare #190 & #180 main jets, and swept cable guides for the carb tops, from Surrey Cycles (Nice people).

For the time being I'll stick with the original throttle slides until I settle on the correct cut away, then I'll get an anodized ones
. I'll also keep the original floats. I may try some Amal conical filters in the future, I just like the look of them.

When the parts arrive I'll make up some new cables.

I'll post an update in due course.
Posted By: BSA_WM20 Re: A65 Carb Question - 02/03/19 8:47 am
You can mount it on a frame rail.
One of the BSA's did exactly that, on the down rail near the oil tank.
Posted By: Allan G Re: A65 Carb Question - 02/03/19 7:01 pm
Some If the more Sporting A10’s. however you need a different lever as the frame rail is usually thicker thank the handle bar.
Posted By: Ianbuck Re: A65 Carb Question - 02/05/19 6:54 pm
A few options for mounting the choke lever, I think central close to the handlebar mounting looks the best option. The thing stopping a pisition near the conttol levers is the low height of the choke lever and the raised screw mounting of the control levers.

I could find some conttol levers with a bottom screw fixing, that would allow the choke lever to be located next to them.


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