n100

Alright I'm not getting any vacuum from any ports on my carb other than the one that goes to the choke. I took it apart and it seems as though every passageway that should go to vacuum is blocked off, not by the gasket but by the carb itself



The hole in red in the first picture is a dead end



This hole in red should exit out by the choke but is a dead end. The hole in blue goes through, but when mated to the otger half is mated to the dead ended hole in the 1st picture<br/>

7T1vette

Don't have any idea whether the components in that carb came together or were 'married' during some rebuild of different pieces later in its life. If you know the history of the carb and believe it to be 'original', you likely checked vacuum on "ported" vacuum points with engine at idle. Ported sources have NO vacuum at idle, but quickly approach same vacuum level as 'manifold' vacuum once the throttle begins opening.

If you are certain that some of the vacuum source passages are blocked or not there, you either have parts that were mis-machined at the factory or non-compatible pieces that were put together during some rebuilding effort.

The only 'manifold' vacuum ports on the Quadrajet (that I am certain of) are the one at the choke area and the ones at the rear and front on the base. The rear is for supply to the power brake vacuum booster and the front port is for incoming 'purge' from the vapor collection canister. The other ports are 'timed' or 'ported' manifold locations for emissions system items.

jnb5101

Some of these channels are very tortuous. Use a very fine piano wire (010) to probe. Hobby stores should have it. In a darken room, shine a small LED type flashlight in one end of the channel to observe any light being emitted elsewhere. Or use a plastic syringe (hobby stores or your dentist will have "impression material syringes") to inject water into a port as a test of patentcy.

lars

The carb shown is commercially rebuilt carb, and it has a throttle plate that is not the same year as the float bowl. It's what we call a "mix-n-match" carb. The components are not compatible with each other. If you tell me what year carb you're trying to create, I can post photos of what the parts are supposed to look like.

Keep in mind, also, that not all float bowls were drilled for the vacuum hole at the choke - many big block carbs did not have this vacuum passage, and the hole is not drilled from the factory.

Lars

lvmyvt76

what year car does the carb need to fit??? I have an extra carb that i would sell very reasonable, it is a commercial rebuilt fron Oreilly auto here in springfield. send a PM to me. Wish I could deliver it to you in Washington!!

lars

I've checked my data base, and your carb throttle plate is not a Chevy throttle plate - it's a complete mismatch to your float bowl and cannot be used with your bowl. It also does not have the power piston APT tang in it, so you cannot achieve proper cruise metering ratio with that throttle plate since your power piston and primary rods will ride much too deep in the jets. Also note that it does not have the PCV nipple in the front edge of the throttle plate - all Chevy Q-Jets have the PCV inlet nipple drilled in the boss that you can see just to the left of the centerline of the throttle plate. Unless you have a "donor" carb to start swapping parts off of, you need to scrap that carb and find something that has not been commercially rebuilt. E-mail me for my "Commercially Rebuilt Carb Problems" paper to get an idea what these commercial builders do to carbs.

Lars
V8FastCars@msn.com

lars

I just tore down one of my original '69 carbs and shot some photos: It would appear that your bowl is a 1969 Chevy. Here is an original 1969 7029207 (69 Vette 350) float bowl – it matches yours (no other year looks exactly like this from the bottom of the bowl):


Here is the correct 1969 Chevy throttle plate that goes with that float bowl. Note the APT adjustment tang located in the slot in the center of the carb between the primary throttle bores and the PCV nipple in the front of the plate:


It also looks like you may not have the correct gasket installed between the throttle plate and the float bowl - there are 2 different gaskets with different vacuum hole locations - use of the incorrect gasket will block the vacuum passages. (Note also the correct appearance of the original hardware - the Torx screws are a sure-fire sign of the dreaded "commercial carb").

Lars

7T1vette

n100...

I'm going to say this as simply and plainly as I can, but you will not be able to detect how emphatically I am saying it:

You need to send Lars an e-mail request [V8FastCars@msn.com] and ask if he would take the carb you have and configure it as needed for your car. He will need info about what engine you have and how it may have been modified, etc. But, your e-mail exchanges with him can detail that info.

His fees are extremely reasonable and you will be getting the BEST Q-Jet carb for the money that you could ever imagine. If he is willing, send what you have to him and let him do his "magic".

'nuf said...

lars

Commercially rebuilt carbs often have a list of problems and issues so long that they are not financially viable to rebuild. If a baseplate without the APT adjustment lever has been installed, chances are really good that the power piston has had its APT pin cut off, destroying the power piston. The carb probably has incorrect jets, primary rods, and secondary rods, and an incorrect power piston spring. By the time you replace all these parts, and the baseplate, you have more into the carb than what you would pay for an unmolested, used, rebuildable carb. However, if the float bowl has the correct numbers for the car, it may be desirable to save the bowl and configure it with all the right parts to make the carb work correctly. This assumes that the commercial builder did not do any "creative drilling" to the float bowl and its calibrated orifices... If the bowl is good, I can certainly configure a "correct" carb around it.

Lars