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Misc: Carburettors Throttle Slide Needle

moto8500

Active Forum Website User
VOC Member
This thread is for the carburetor aficionados amongst us.

I am running the Shadow on a pair of Amal standard carbs 1949/54 and the plugs run for 300ish miles before fouling up.

Air screws are set for optimum running at tick over.

I had the same problem with the BSA Goldstar so I lowered the throttle slide needle one notch and hey presto no more running rich and I achieved a decent tick over.

I have not looked at a diagram of the Shadow carbs so don't know if the slide needle is graded with notches but that aside would consider lowering the needle to cure a rich running engine with the existing needle jet?
 

Bill Thomas

Well Known and Active Forum Website User
VOC Member
Can't say for sure,
But most of our running is on the slide,
On my bikes , Not standard Carb's , Some years ago I had a lot of plug wetting,
I think because of the rubbish petrol we now have ,
So I changed to weaker slides, ie Bigger cutaway,
Also I use the best petrol now all the time.
Good Luck, Bill.
 
Last edited:

Bill Thomas

Well Known and Active Forum Website User
VOC Member
This shows you where the throttle is for what part of the carb' to tune.

Chris on here told us to mark the rubber throttle grip 1/4 , 1/2, 3/4, etc,
So you can have a quick look down to see where you are at what speeds.
 

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greg brillus

Well Known and Active Forum Website User
VOC Member
Well it all depends on what slides you have........usually a number 4 is standard........a number 3 will generally be too rich.........there are 3 1/2 available as well.......and these can work ok, although i have found these to be rich as well.........If the carb parts are in good condition, then the first thing to look at is the float levels, as these will make the engine run rich........a quick check is to simply stand a couple of meters behind your bike with the bike upright, and check the visual alignment of the carb/bowl in relation to the vertical case/engine lines. If the bowl is high or low, you will see it quite easily........then simply rotate the carb complete via the clamp/bolt on the manifold stub and this willl put things in the ball park.........actually checking the float levels acurately involves making a simple tool from an old carb bowl attachment banjo bolt with a brass nipple drilled/taped into the base of same, then a length of thin clear tube slipped over this fitting and the fuel level can then be checked against the carb itself........should be just bellow or level with the base of the mixture adjusting screw........this level is often not correct and will affect the general running.......plug checks are worth doing and a slightly sooty look is normal, but not absolutely black as this is obviously too rich.........Good luck with it all.
 

Bill Thomas

Well Known and Active Forum Website User
VOC Member
Just had a thought , Maybe your Spark Plugs are Too Hard / Cold,
Not keen on NGK , But if you have them I think they should have a 6 on them ?,
I prefer Champion, N5c or N9Yc. Only about 20 thou gap.
 

moto8500

Active Forum Website User
VOC Member
Thank you very much for your replies as it has given me other options to consider in addition to lowering the throttle needle which was the purpose of the thread.

I have tried a variety of plugs and currently running on NKG 7 but they all suffered from the same fouling issue so taking into consideration the replies I am confident I will crack it.
 

moto8500

Active Forum Website User
VOC Member
I am sure you are right - the colder the plug the more the deposits build up so at some point I will try a 6 or the one's Bill Thomas recommends and see how they perform.
 

Bill Thomas

Well Known and Active Forum Website User
VOC Member
I don't know about your bike ,
But a lot of Vincents are a bit oily,,
Mine are ex race bikes , So the pistons are a bit more loose ,
 

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