Throttle body gap setting of . 002" is pretty hard to detect. But I notice that as mine is set now, the tiny hole for the vacuum is compleyely ABOVE the plate and my .002" feeler is totally tight by the plate pressure

But when my feeler guage just gets a wee tight at .002", the tiny hole is about half covered by the plate.

Can anyone comment as to " half covered" being a good visual refetence?

Anndddd...how the hell does one adjust the gap while TB in car. The stop bolt is almost totally inaccessible..but maybe the two adjuster nuts on either side of the throttle cable mount should be used? Kind of like the adjuster on a bike brake setup maybe🤔

Thanks!!

 

I guesd I have to figure a way to get to that crusty stop bolt and lock not. Seems impossible ☹️.

 

Still hoping for some education on the throttle body and the reason for the .002" gap.

First question, is the gap ONLY crucial for the tiny vacuum hose hole that connects to the distributor
via the CARB connection on the distributor vacuum regulator. I have to believe this is just for
vacuum advance.

Or.... is the gap more relevant to allowing air flow into the intake manifold at idle?

Just hoping to learn exactly why the .002" gap is so important and how it affects the operation.

Current setting has the TB plate completely below the vacuum hole.



Thanks - Randy

 

Rnady:

Methnks you are over thinking !!!!

The gap allows air to enter the engine. Result in idle speed in rpm's. .002 is the design opening to attain the design idle rpm. We did this by ear in carb days!!!

The hole is for ported vacum. relates to the advance diaphram on the distributor.

Why are you wanting to mess with it? Does the car run OK?

 

Hi Carl

Thanks for reply. The "why" is because I have lits of "bits" removed at the moment to replace hoses, vac lines, fix oil leaks etc. So while off I wanted to check/set gap. In posts about lumpy idle, always a step to clean TB and set proper gap.

Devils advocate..if that gap is to allow proper idle, why is there an idle adjust screw.

The engine was running fine previously except for lumpy idle. As far as the vac advance, it makes sense to NOT have vac at idle, hence plate below little hole.

I am getting close to getting my "old timer" card, but I have tinkered with my 75 2002 and Weber 32/36 for 10 years so I know the joy of "by ear" 😊

My favorite old timer tip of all time when setting timing and carb...place a clear cup of liquid (beer is always around for some reason!)..on the engine. Then watch the ripple patterns in the fluid. When they are calm and flat the motor is happy and running smoothly!!

Randy in Raleigh

 

Randy:

I can only speculate that the idle adjust is to fone tune the air intake and thusly idles RPM'.

If the butterfly is clean, leave the gap alone/ Do not fix what ain't broke.

I put a Webber carb on my Turbo Corvair. I had a ball with the infinite tune options..

More fun before the Jaguar. Two r three carbs on a warmed up Ford flat head V8.
Three looked snazy. Two ran best !!!!

Trusty vacum guages for tune...