Vacuum start switch timing shims

[old-tank]

It has been a long time if ever that I removed and or added shims to make the switch engage sooner or later.  Seems like the plastic on the contact section would need to be spread which might result in breakage --- maybe the plastic was more pliable when new.  (55 WCFB)

Edited December 8, 2019 by old-tank (see edit history)

[jw1955buick]

What do those shims look like? I’m doing a carb rebuild, just pulled that switch and there were no shims at all

[jw1955buick]

The manual points to where they go, but doesn’t actually show any shims, just points to the end of the plastic piece 

[avgwarhawk]

I would suspect the shims to be pliable when new. I did not remove the vacuum switch when I replaced the gaskets on my Carter. I can not comment with any certainty.  However, I noticed that the Rochester switch on the 60 requires more pedal movement to engage the starter. Once warm it requires much less pedal movement to engage the starter. 

[old-tank]

16 hours ago, jw1955buick said:

The manual points to where they go, but doesn’t actually show any shims, just points to the end of the plastic piece 

Page 340 of the service manual has more poor illustrations and explanation.  But until you have one of those switches in your grubby little hands...

Anyhow, I found a switch with a bigger stack of shims that I installed yesterday and will give it a try this morning.  It seems to crank earlier (less depressing of accelerator), but need to see if it still unloads the choke and fast idle cam.  The trouble with adjusting choke related actions is that it is not repeatable after a few starts.  More later...

[Beemon]

I wonder if it would be possible to use a laser engraving CNC machine to cut these out of a thin nylon sheet. 

[old-tank]

Well it starts as designed and like it did before with the switch with the higher stack of shims.  And I did figure out how to disassemble:  pull off the spring and then the washer and you can access the shims to add or subtract.  Adding 0.015 more shims resulted in about an inch of less travel of the accelerator pedal to activate the starter.  That was enough to prevent unloading of the choke while cranking and kicking it off the fast idle cam after it did start.  Even with a perfectly adjusted choke, everything else has to be timed to work correctly!

So, why am I messing with this?  The original carburetor had severe vacuum leaks around worn throttle shafts requiring a base idle of 800 rpm to keep it from dying when put in gear.  I found  the lower throttle body section with good shafts and exchanged that part only.  That part had been "messed with" by others: missing idle mixture screws and idle adjustment screw (swapped from old part); the vacuum start switch was gummed and stuck (probably not used) and the fast idle adjustment was turn out to be ineffective.  (even when rebuilding a WCFB none of this stuff needs adjusting if it was working as designed before the rebuild)  Now I can idle it down to 500 rpm and the engine speed stays above 450 when put in gear.

Thanks for your interest!

[jw1955buick]

mine Is filled with some type of grease, what did you put in yours if anything? 

I was going to use some dielectric but can’t find info on it 

[old-tank]

I never used anything...and the service manual makes no suggest ions.

[jw1955buick]

Okay, my plastic switch body has what looks like old brown wheel bearing grease in there, who knows why...thanks!

[avgwarhawk]

10 hours ago, jw1955buick said:

Okay, my plastic switch body has what looks like old brown wheel bearing grease in there, who knows why...thanks!

 

To allow the parts inside(ball bearing and plunger) to move as vacuum increases.  Sometimes it requires cleaning and new lube.   

Edited December 13, 2019 by avgwarhawk (see edit history)

[Beemon]

I have never used lube on any part of the switch. If it were mine, I'd clean it out and leave it without grease. You really don't want anything getting stuck or clogged in this circuit.