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Hello all, I have a 235 six in my 1936 chevy pickup w/a rochester 1b carb & I'm having vacuum issues; I set the timing to spec & when I checked the vacuum the needle stays in the red & says late ign timing or leak at intake manifold, I then sprayed all connections w/soap (as well as the line coming from the carb but found no bubbles (with line disconnected & plugged) I then removed carb & checked the ceramic spacer & it looks new; there is a hole in the manifold where the carb bolts but is blocked by the spacer. I'm out of ideas, Any suggestins? All help is appreciated. Thx Richard. PS, When I reconnected the line to vacuum advance it advanced the timing.

Note added later: only do this after reading the post/suggestions/question in the message below.

Hello, bebop40,

Try slighting opening an unlit propane torch around the base of the carburetor and all intake lines/parts while the engine is idling. If the idle speed changes, you have found a leak.

How is the engine running besides the vacuum problem? If you advance the timing, can you get vacuum?

Are you reading the vacuum at the manifold or carburetor?

You may have the gauge plugged into a ported vacuum port instead of full time vacuum, is the port above or below the throttle blade?

Joe

Hello Joe, The engine runs fairly well but feels like something is holding it back, not real smooth, I have a vacuum port at the intake manifold that is plugged off; I diconnected the line that comes fron the carb (above the throttle plate) & goes to thevacuum advance. no the vacuum does not increase when raising the rpms, upon reconnecting the line at the vacuum advance pthe distributor immediately advanced at idle.

bebop49,

I think the vacuum above the throttle plate (ported vacuum?) is not useful for obtaining vacuum at normal idle speed.

Can I run full vacuum straight off the intake manifold to the vacuum advance?

You can do it, but you probably should not do that?

vacuum doesn't blow bubbles, it sucks, need to use the propane as Tim suggests - instead of reconnecting it, try just plugging it off, which may be what you're doing connecting it with that hole blocked by the spacer, will prolly act the same as "reconnecting" it

Bill

Hello again everyone, I tested the manifold & carb w/the propane torch & no increase😖 in rpms; however connecting the vacuum gauge to the line that goes to the v advance & manually raising the rpms by the throttle, the needle moved up to about 22 degrees & on deacceleration dropped back to the red zone. 😖. any more ideas?

Does your carburetor insulator look like this (it is usually bakelite, not ceramic)? Ceramic would be better than metal (I have seen metal "insulators").

Does your insulator have slots as shown in the image above?
Is one of the slots under an opening in the base of the carburetor?

Yes the insulator looks like that. It is bakelite, not ceramic (my mistake) There is a gasket that sits on the manifold under the insulator & also a gasket between the insulator & the carb.

Are the slots in the gaskets and spacer aligned with the port on the bottom of the carburetor?

Connect the vacuum gauge to the port in the side of the intake manifold directly below the carburetor mounting flange. If there isn't a vacuum nipple there, install one. You're wasting your time (and ours) trying to use distributor vacuum for tuning.
Jerry

"Does your insulator have slots as shown in the image above?
Is one of the slots under an opening in the base of the carburetor?"

ditto ditto

Adding to the confusion.

ALWAYS connect the vacuum gauge to the port below the carburetor on the intake manifold. Using the ports on the carburetor give incorrect readings.

I have not had good results using propane to check for intake leaks. I use carb cleaner or brake cleaner.

Use of a vacuum gauge for diagnostics. http://performance-diy.blogspot.com/2012/04/vacuum-gaugereading-and-interpretation.html

Using a vacuum gauge for timing & tuning. I quit using a timing light on these engines years ago. http://automotivemileposts.com/garage/v2n8.html

Fred, I'm interested in hearing about how you are checking the operating range of the centrifugal and vacuum advance with a vacuum gauge? My delay flash timing light does a good job of that.
Jerry