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Advice on where to go for help with carburation?

BlackLightning998

Well Known and Active Website User
VOC Member
Hi,

I wonder if someone could recommend where I could take my bike for assistance with what I think is a carburation problem. With 1600 miles of running in complete the bike has had what I could best describe as a slight stutter/hesitancy on a constant throttle setting which clears when you open the throttle and accelerate. She runs happily up to this point and you can accelerate through it cleanly too. This problem equates to about 55mph in 4th. My rudimentary experience would suggest fuelling is the issue. The bike is running 12 volt electrics, Pazon Ignition and re-wound dynamo - all seems to be working fine from everything I can tell. The engine has been competely re-built but the carbs have not been refurbished - she starts easily, ticks over happily and runs beautifully with healthy coloured spark plugs - just this one annoying issue on a constant throttle. Pipes are colouring properly and well.

I've tried one/two fuel taps open, I've tried full tank/half empty tank and everything inbetween. Air slide levers don't appear to have any effect on the problem. I haven't touched anything on the carbs yet as it may well be beyond my capability and I'd rather not cause any damage! I have thoughts about cleaning the tap filters - but more in hope than in expectancy.

The carbs are certainly elderly, the slides feel a little "sloppy" in the bore.

So I'm thinking that I need a specialist to help me out. I'm in the South end of Buckinghamshire - anyone got any ideas on where to take it?

Thanks

Stuart
 

Vic Youel

Well Known and Active Website User
Non-VOC Member
What sort of carburetters are they Stuart? I think you are correct it is a carb. problem; I have a similar problem on my Matchless 650 which only uses a single carb.

Your problem may be something simple like the carbs have just got out of balance in the running in process. Are you using a twin cable or single cable throttle?

Vic
 

BlackLightning998

Well Known and Active Website User
VOC Member
What sort of carburetters are they Stuart? I think you are correct it is a carb. problem; I have a similar problem on my Matchless 650 which only uses a single carb.

Your problem may be something simple like the carbs have just got out of balance in the running in process. Are you using a twin cable or single cable throttle?

Vic
Hi Vic,

Nice to meet you Sunday, thanks for the interest and reply.

They are original Amal inch 1/16th (I think that's what you call them) although they have been put together using Series D bolt on manifolds at some point in their life.

The throttle is a two cable job, and I've checked routing and both cables are operating pretty freely and there are no right spots. There are adjusters on the cables close up to the throttle body.

Now - balancing carbs with a two cable throttle - how do you go about doing that then!!!!

I'll give people a few laughs on this Forum with my very low level of knowledge as yet - but I'm keen to learn. The CBR 1000 4 carbs get balanced with a gauge when they go tot the garage, and the Ducati has fuel injection. I know the principles but the library is growing only slowly, Know Thy Beast and Riders Handbook so far.

On an issue like this one I'd prefer to get some proper help rather than risk damage, you can do some serious stuff running too lean/rich can't you?

Cheers

Stuart
 

stumpy lord

Well Known and Active Website User
VOC Member
carb balancing

Hi Stuart,
Balancing carbs on a vincent is not very hard, all you have to do is place the machine on its stand and with the digit finger of your left hand up the bellmouth of the rear carb[ finger lightly touching the rear slide]lean over the machine so that you can see the front carb slide,and with your right hand slowly and gently open the throttle. this way you will be able to ascertain which carb is leading , and be able to adjust as necessary on the cable adjusters.
Not as hard as it sounds.
cheers norm.:eek:
 

johncrispin

Well Known and Active Website User
VOC Member
carbs balancing etc

Stu,
You are fortunate in having 276 carbs which can be completely replaced if you so wish. New slides needles etc and (carbs) are available from Surrey Cycles and he always has his trailer at Kempton. I purchased new needles for mine from him which made a big difference.One of the chaps there on Sunday (with the big Yamaha, Steve Wheeler from Sussex section, does a lovely job of refurbing original carbs.
I have to say that I do not prefer the junction box on the VIn and have twin cables which using Norms method is simple. Every time you remove the tank you will have to do this.
My own system is to put a pen under one slide and be able to just slide it out under the spring pressure on one carb, and adjust the other carb the same, this helps to compromise the difference in lengths and the cable routing. Weakness is the enemy in terms of potential damage and I doubt that is your problem given everything else is OK. I also put an extra heat insulating spacer between the manifold and head, those carbs can get very hot especially in traffic.
 
Last edited:

BlackLightning998

Well Known and Active Website User
VOC Member
Hi Stuart,
Balancing carbs on a vincent is not very hard, all you have to do is place the machine on its stand and with the digit finger of your left hand up the bellmouth of the rear carb[ finger lightly touching the rear slide]lean over the machine so that you can see the front carb slide,and with your right hand slowly and gently open the throttle. this way you will be able to ascertain which carb is leading , and be able to adjust as necessary on the cable adjusters.
Not as hard as it sounds.
cheers norm.:eek:
Hi Norman,

Sounds straightforward to me - I like it. I guess the aim is to have the slides doing the same thing at the same time then (seems obvious when you say it quickly - balanced).

I'll give that a go and then try a ride. So long as I stay in the rich side there's probably not too much going to go wrong I guess.

Once I've done this and lets suppose it makes no difference, would the next step be to lift the needles on both carbs one notch (plugs are a nice tan colour already, and the exhaust pipes are colouring nicely too)?

Thanks for your help.

Stuart
 

BlackLightning998

Well Known and Active Website User
VOC Member
Stu,
You are fortunate in having 276 carbs which can be completely replaced if you so wish. New slides needles etc and (carbs) are available from Surrey Cycles and he always has his trailer at Kempton. I purchased new needles for mine from him which made a big difference.One of the chaps there on Sunday (with the big Yamaha, Steve Wheeler from Sussex section, does a lovely job of refurbing original carbs.
I have to say that I do not prefer the junction box on the VIn and have twin cables which using Norms method is simple. Every time you remove the tank you will have to do this.
My own system is to put a pen under one slide and be able to just slide it out under the spring pressure on one carb, and adjust the other carb the same, this helps to compromise the difference in lengths and the cable routing. Weakness is the enemy in terms of potential damage and I doubt that is your problem given everything else is OK. I also put an extra heat insulating spacer between the manifold and head, those carbs can get very hot especially in traffic.
Hi John,

Many thanks - should have asked the question on Sunday and saved the Forum space, although I'm chasing Graham hard for the "Top Poster" award - that's p.o.s.t.e.r.......

Like your idea with the pen, then I guess the only variation will be the length of the cables and the slack take up in the cable across its length - shouldn't be too much I guess.

Would the carbs being out of balance cause the symptoms I have described do you think?

Thanks again.

Stuart
 

soloman4040

Website User
Non-VOC Member
The Red Dragon

Quite a pleasant task, first go and have a night out with good company and enjoy the delights and accomplishments of a chinese restuarant. Insist upon retaining the chop sticks after consuming the meal. subsequently wash and clean said chopsticks dry carefully then*****bung the thin end of said inscrutible chopstick one per carb to nicely balance, pivoting each against its respective slide. opening the throttle carefully will cause said chopsticks to droop indicating difference of movement between slides magnified of course due to length of said inscrutible chopstick. Ho Ho Ho.
 

Simon Dinsdale

VOC Machine Registrar
VOC Member
VOC Forum Moderator
Quite a pleasant task, first go and have a night out with good company and enjoy the delights and accomplishments of a chinese restuarant. Insist upon retaining the chop sticks after consuming the meal. subsequently wash and clean said chopsticks dry carefully then*****bung the thin end of said inscrutible chopstick one per carb to nicely balance, pivoting each against its respective slide. opening the throttle carefully will cause said chopsticks to droop indicating difference of movement between slides magnified of course due to length of said inscrutible chopstick. Ho Ho Ho.

Great idea. Always looking for an excuse to go to the superb local chinese restaurant. Before anyone asks - China Moon just off A1 at Markham Moor roundabout north Nottinghamshire.

Cheers
Simon.
 

BlackLightning998

Well Known and Active Website User
VOC Member
I like your style, sounds like fun and the geometry makes sense - bit like the Egyptians building the Pyramids then, levers, fulcrums and all that.................

Looking forward to having a play and reporting back.

Does everybody think the issue is likely to be a carb imbalance then rather than anything more sinister - the hesitation and stuttering I describe?

Stuart
 

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