DUI Vacuum Source - Manifold or Ported? (1 Viewer)

[JohnJL]

Hi All,

I have a desmogged 1974 fj40 with original Aisin carb and a DUI distributor. I am struggling to get my idle set right and am going back over everything...I have the DUI manual but it is not specific. WHen I had this distributor running my motor before, the motor was smogged and with that black box emissions thing, I am not sure if the source was manifold or carb-ported above the throttleplate..

Can someone please confirm it DUI distributors with vacuum wants manifold vacuum or ported vacuum?

Also, do you guys lock the distributor timing and disconnect the vacuum advance on the distributor when tuning the carb idle mix and plate position?

Thanks!

 

[1911]

Paging @Solace in Solitude ...

He has a lot of experience with DUI dizzy's.

 

[Solace in Solitude]

DUI needs ported vacuum.

I'm only familiar with my '78, but I think your ported vacuum should be near your idle-mix screw.

My '78 is desmogged

timing set at ~12*BTDC... DUI locked down

Plugs gapped at 050"

If dialing in my '78 oem carb, I remove the vacuum line and cap the carb port... Lean-Drop the idle mixture, with idle set at 650 rpm... screw in until engine starts to die... unscrew 1.5 turns... then unscrew further, until it begins to ping... screw it back in until no ping... uncap the carb port... reconnect the vacuum line.

If you have trouble making your engine die, while lean-dropping, you probably have a vacuum leak.

 

[JohnJL]

Awesome, thanks. I have the DUI connected to the intake manifold right now, which would explain the problems I am getting the motor to behave as I would expect. I will have to hunt for a ported source...I have one on the secondary on my carb...I am not sure that will work or if I need a port source above the throttle plate on the primary side?

 

[JohnJL]

Awesome, thanks. I have the DUI connected to the intake manifold right now, which would explain the problems I am getting the motor to behave as I would expect. I will have to hunt for a ported source...I have one on the secondary on my carb...I am not sure that will work or if I need a port source above the throttle plate on the primary side?

Also I've emailed DUI do check the source...and let them know their instruction manual is offline...

 

[JohnJL]

huh...I got an email back from DUI that says manifold vacuum is preferred....

 

[Solace in Solitude]

Maybe I’m wrong... If so, I apologize.

I always assumed the vac advance port (Gold arrow on pics) on my ‘78 carb, was ported vacuum... this thread talks about the vac adv port and refers to it as ported.

My oem dissy pulled vac adv from the vac adv port... I connected my dui to the same port.

It starts, first time, every time... and runs great!!

I can tell you, I accidentally swapped vac adv and TP once... it ran great, but required choke to start... even when warm.

There’s been a lot of discussion about ported vs manifold, here on MUD. I have no idea what the consensus is... but, mine works great!! Read thru this thread —> Distributor Vacuum

Another thread, with @FJ40Jim’s input.—> DUI advance adjustment ?

I don’t remember you saying what carb you have... Does it have a vac adv port?