Welcome to our Site for MG, Triumph and Austin-Healey Car Information.


MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGA - Syncroniser - hole or not?

Here is one for Steve Gyles! Should the carb syncroniser have a hole in the flange to allow in air like the gasket between the carb and air cleaner. My syncroniser flange covers all the holes other than the carby throat.
Mike Ellsmore


Are you trying to bait me?!! I am trying to visualise what you mean. Any chance of a photograph?

Steve Gyles

Good question Mike!

That is, I take it, you are referring to the device for balancing the carbs during tuning?

Steve, if I have understood correctly, Mike references you because of your pet subject of air cleaner back plates being fitted upside down (and blocking the holes).

Mike I have never seen such a thing and never thought it would make any difference as you are doing the same (blocking the holes) to both carbs. There are balancers that just fit inside the carb throat though.

I was just doing this yesterday on an MGB and using the synchroniser with the foam rubber flange. I am pretty sure that it is possible to get a very accurate balance.
Neil MG

Firstly apologises for spelling synchronizer incorrectly. Yes Steve I was checking to see if you were around. But seriously i just tuned my carbs after a major rebuild and used the synchronizer tool in the attached photos. When i put it over the carb opening the revs dropped substantially - i wondered whether blocking off the hole in the flange was the cause (i immediately thought of Steve). Anyway i carried on and synced them using the ball rotameter on the tool to the same reading. Car is running fine but i thought i would raise the question to see what people thought.

Mike Ellsmore

This is a photo of the side of the synchroniser that abuts the carby flange.

Mike Ellsmore

Guess it will not matter when balancing ( so long as the engine keep running) as you are treating both carbs the same but clearly the hole must be open to atmosphere for normal running. This hole allows atmospheric pressure air to the underside of the piston in the damper chamber to allow it to rise when vaccum is applied to the top side of the piston from the engine sideand also fall when the vaccum reduces. Look at a cutaway drawing and all will become clear. Google SU carburetor
A J Dee

Why do you need a tool like that? A piece of 8mm plastic tubing with one end stuck in my ear and the other held at the carb throat is all I need. Then I adjust the carbs so they sound the same. If they play the same note when the tube is held in the same position, the carbs are synchronised. That's why it is called tuning! With a musical ear you can get it spot on in no time at all, just by constantly moving the tube back and forth until there's no difference in the sound they play. Then it is only a question of tightening the links and setting the mixture.
dominic clancy

Hi Dominic, yes it is a bit of a gimmick but it does work well and is based on sound scientific principles - if you spoke with my wife she would tell you I'm tone deaf when it comes to music. I set the mixture before synchronising.
Mike Ellsmore


My balancer has a cone on the carb side so it is well away from the holes in the carb. However, it also has adjustability to allow some air to pass through the device so the carbs do not stall the engine.

I believe yours also has this adjustability.

P. Tilbury

Firstly I don't think blocking the dashpot breathers with said tool should make any difference at a set throttle speed, especially at idle as at idle there isn't really much suck going on in the dashpot

BUT having said that, there shouldn't be a revs drop when you offer up the tool to the carb as this will throw the reading out

Try having your engine idling and block the holes on one carb with your fingertips - If the revs drop,then the tool blocking the holes is the problem
If the revs don't drop then there is a problem with the setup of your tool that needs addressing, There is probably some sort of bypass air adjustment available to you there-------
William Revit

I have exactly the same tool as Mike and I do not have any significant drop of revs using it.

There is a University Motors video on carb tuning (MGB HIF) on Youtube and I think John uses the same tool too.
Neil MG

This thread was discussed between 21/03/2015 and 24/03/2015

MG MGA index

This thread is from the archives. Join the live MG MGA BBS now