48 replies to this topic

[KernowCooper]

Vent A to atmosphere and B appears to be engine side of the butterfly so subject to engine vacuum so either its a take off for a vacuum gauge or if you dont have the small spill centre in front of the vac slide cover and flange for a vac advance its a odd one.

 

Try it for now with B blocked off and A vented to atmosphere see if it starts and idles

 

 

Update just blew up the photo sure I can see the spill for the vav advance unit with the yellow line through  it. If i'm correct put vac pipe from the distributor on the spill, blank B unless you have a vac gauge to connect, and vent A to  atmosphre and try and start and set idle.

Edited by KernowCooper, 06 October 2014 - 08:06 PM.

[Earwax]

just beaten to it....... go Kernow!!!!

 

i agree  your label a)   crank breather just leave vented

 

            your label B   vac advance for dizzy .... block off or connect to dizzy

 

 

and bottom  unlabelled fuel in and overflow   .. don't know which is which 

[KernowCooper]

I think the Vac Advance is where the yellow line goes between A-B like normal SUs? and B is a engine Vac Take off as it appears to be drilled into the carb flange which is engine side of the butterfly ? and therefore subject to pulses of engine vacuum, not good for a vacuum unit.

 

Have a gander close at the picture and see if you agree the vac spill take off appears to be in the normal place. Then blank B.

Edited by KernowCooper, 06 October 2014 - 08:20 PM.

[GraemeC]

Surely Silve1999's post tells you what you need to connect to what on an identical carb?

[KernowCooper]

I dont think its right though ? says connect the  vac connection to the top vent pipe, to late at night to keep look at pictures fresh eyes in the morning

[silve1999]

http://www.theminifo...tion/?p=2224394

 

 

 

 mbimage (1).jpg   86.32K   18 downloads

Edited by silve1999, 07 October 2014 - 08:47 AM.

[KernowCooper]

I see in the above picture the carbs on the table and not running on a car with the pipe work connected, just thinking aloud if you connect a pipe onto the connection from the carb flange which with the engine running its subject to engine vacuum if  you then connect this to the the float chaber vent it then subjects the float chamber to vacuum, so in effect engine vacuum can then draw fuel up by passing the needle and jet.

 

The carb in the picture above appears to have the vacuum pipe from the carb flange onto the float chamber overflow ? not where youd have a connnection on a running car.

[Bradshaw-s]

Hey guys,

 

Thanks again for the info, I have actually piped the carb up as in the picture & as per link from Silve999 & still no joy - it refuses to idle without choke.

But (see above picture) if I blow air into the the bottom pipe (below the black breather cap) the engine starts to idle - not sure what this means except it is pushing fuel up the jet into the body/throat of the carb.

Cant play with it for too long as I run out of breath!

The carb has been stripped & service kit installed as per SU OEM instructions, so the jet is new, needle is new & all grommets, seals & gaskets are new including setting the float level as per instructions.

Si

[Bradshaw-s]

Hey Dave,

 

The configuration you have just suggested I have not tried yet - I understand in principal that this should work as it will create a lower air pressure in the reservoir.

The flange connection - should this have the same vacuum 'pressure' as the specified vacuum take off of to the dizzy?

As it seems to be a little less from memory - but will double check when I get back to the garage.

 

Si

[KernowCooper]

Vacuum takes off engine side of the butterfly are subject to strong vav pluses not what a distributor wants, the vacuum take off for a distributor is the small spill with the pointed top which is behind the throttle butterfly.

 

When you have it running on choke have you sprayed around the manifold with wd40 to see if its drawing air ?

 

Try it with B on the flange blocked off and A vented to atmosphere see if it starts and idles

Edited by KernowCooper, 07 October 2014 - 01:30 PM.

[Bradshaw-s]

Hey Dave,

 

Yes I have tried WD40 everywhere around the manifold & all gaskets - will try what you have suggested tomorrow.

Just 2 questions -

Can air be drawn in through the throttle spindle - enough to cause this issue?

If the butterfly is not fully 'closed' when closed - fraction still open would this cause the issue?

 

Si

[KernowCooper]

Throttle spindle would allow you to run without choke, and give a erratic idle depending how or how much the spindle was worn, more so on twin carbs, catch it hold and feel  for play, the butterfly woulld never be fully closed the engine would stall and not idle, thats what the idle screw does it lifts the butterfly to allow fuel/air in to idle.

Edited by KernowCooper, 07 October 2014 - 04:46 PM.

[jaydee]

The connection A-B is an economy device 

You have two options:

- connect A to B

- Blank BOTH

Otherwise you have a MASSIVE air leak.

 

And please get rid of that pancake really.

[Bradshaw-s]

Ha!...leave my Minispares pancake alone!!! £15 of quality lol!!

 

I did connect A to B initially - still no joy...hence this whole thread!

 

si

[jaydee]

Its time for a strip down and inspection then. Especially the float bowl.

Personally i wouldnt bother with the device and just block the two connection.

Heres a description of the system:

 

 

 

Edited by jaydee, 07 October 2014 - 07:12 PM.