Weber Carb Synchronisation

[Peter MarieEa]

The 45 DCOE's on my '94 VX HPC cannot be perfectly synchronised by the synchroniser screw. The right barrel of each carb' has about a 10% lower flow value than the left barrel; the cars idle quality is not great.

Is it possible to individually adjust the throttle valves on the spindles? What sort of flow variance between barrels is considered acceptable?

Any thoughts?

 

 

 

Quick7

[ian balson]

Peter,

 

You may have some air-bypass adjusters, under the white plastic caps(fig 25/26 on the html below). I have on my 93 VX. These can be used to adjust the indivdual throttles.

 

I take a reading via the Vacuum Take Off (fig 48), in order to read the value on the engine side of the butterflies.

 

http://www.webcon.co.uk/weber/45dcoe.htm

 

Rgds

Ian

[Peter MarieEa]

Thanks Ian

So that is what those white plastic caps are!

 

 

Quick7

[Peter MarieEa]

Ian

The Vacuum Take-Off Cover I presume is the same as the Progression Hole Inspection Screw. What do you use; a suitable hose and Vacuum Guage? Do you use this instead of a carb' flow meter or in addition to it?

I trust you're still not up at 1:00 am your time!

 

Regards

Peter

 

Quick7

[Slomove]

I played with the bypass screws (my butterflies are also slightly off sync, maybe due to a twisted shaft) so that I got even reading on the Carbtune vacuum sync meter. That satisfied my engineering curiosity but I did not get the feeling the car had "better" tickover or running in the progression range. I ended up closing the bypass screws and I am not sure if they are really useful. Even with the small asymmetry the car runs better. That may be due to the fact that, while the bypass can balance the air pressure drop across the closed butterflies, they do not balance the fuel mixture. But that is just a guess.

 

Gert

[ian balson]

Peter,

 

No, the vacuun take off covers are separate from the Progression hole covers. They are the brass screws just to the inside the Idle adjusters/Progression hole covers.

 

I use a Morgan Carbtune (http://www.carbtune.com/) to balance my carbs. The hoses just screw into the vacuun take off holes. I have an ITG Foam filter on my VX, so the flow meter was not too easy to use.

 

Great fun these Carbs aren't they !

 

Rgds

Ian

[Peter MarieEa]

I wish I checked the Air-Bypass Adjusters before as they were way off; all four had been backed off 1/2 to 2 full turns! Following my Weber Manual instructions I seated all the adjusters and with an air flow meter I found the left and right barrels of each Carb' to be pretty close. A 1/4 turn out of each left barrel was all it took to synchronize each Carb'. I then reset the Idle mixtures.

The idle and low speed running is much better. Ian, as you may know I'm running Roger King's recommended jetting in my standard tune HPC. I don't know if this is common to all VX engines but my mine doesn't like the idle set anything below 1000 rpm otherwise it will stall readily. 1050 or 1100 rpm is about it without any extra load such as head lights and or the rad' fan. I really would like a hand throttle to adjust the idle speed from inside the car like I have on my Twin Cam Europa with Zenith Strombergs; actually that is about the only good thing about those Carbs' vrs Webers.

"Aren't Carbs' Fun" .... Give Fuel Injection any day!

 

Regards,

 

Peter

"Aren't Carbs fun."

 

Quick7