1970 L46 new carb today, question...

[Greg H.]

I have my rebuilt correct Q-jet carb today for my L46 replacing a loaner Q-jet that was from some other Chevy. My problem is the vacuum line looks to be going into a different location. Here is a pic showing the "correct" carb with the vacuum tube heading toward a plugged port. The fitting from the incorrect carb still in the tube. This port on the "correct" carb is plugged, and there is an open one on the passenger side. The tube is a larger size as well.

If someone has an original L46 please tell me where the vacuum goes. I'm dying to start her up!

Thanks,
Greg

[Thomas H.]

Re: 1970 L46 new carb today, question...

Greg,

I connect this port to my vacuum advance. It may not be the correct routing for the emissions set up on a 70, but it provides full time vacuum to the advance pot. It will get you up and running.

I'm sure others will provide better advice on the "correct" routing for the emissions set up on a 70.

Tom

[Greg H.]

Re: 1970 L46 new carb today, question...

Thanks, Tom. Up and running today is the goal. Tomorrow I can route it correctly.
Greg

[Thomas H.]

Re: 1970 L46 new carb today, question...

Greg,

Looks like we are in the same neck of the woods as well as the same generation! Small world..........

Tom

[Joe L.]

Re: 1970 L46 new carb today, question...

I have my rebuilt correct Q-jet carb today for my L46 replacing a loaner Q-jet that was from some other Chevy. My problem is the vacuum line looks to be going into a different location. Here is a pic showing the "correct" carb with the vacuum tube heading toward a plugged port. The fitting from the incorrect carb still in the tube. This port on the "correct" carb is plugged, and there is an open one on the passenger side. The tube is a larger size as well.

If someone has an original L46 please tell me where the vacuum goes. I'm dying to start her up!

Thanks,
Greg

Greg-----


I believe that the 1970 vacuum advance line is connected to the vacuum port which can clearly be seen on the upper passenger side of this carb. The lower vacuum port, as used for 68-69 applications, was either plugged or non-existent.

By the way, the stud-and-nut configuration you have for the forward carb retaining bolts is incorrect. 1970 used flanged head bolts.

[Greg H.]

Re: 1970 L46 new carb today, question...

Thanks, Joe. As I get further into this I'm finding a few other things incorrect with this unit. Appreciate the help. I've got more work to do.

[Bill L.]

Re: 1970 L46 new carb today, question...

The vacuum connects to the TCS switch front port on the passenger side. There should be a metal tube between two pieces of vacuum hose. The back side of the TCS switch also has at least one vacuum hose that connects to a vacuum nipple at the top back of the carb. I took mine apart or I would take pictures.

If you have a Vette Vues Fact Book, there is an excellent picture on the back inside cover showing the correct routing. If memory serves me it is also shown in the assembly manual.

Hope that helps.


Bill

[Terry M.]

Re: 1970 L46 new carb today, question...

Yes, the vacuum hose routing IS in the 1970 AIM.

[Patrick H.]

Re: 1970 L46 new carb today, question...

By the way, the stud-and-nut configuration you have for the forward carb retaining bolts is incorrect. 1970 used flanged head bolts.

FWIW, I've got similar ones from ARP on my 71. With Grade 8 washers under the nuts, I like them much better than the original bolts.

Patrick

[Dennis D.]

Re: 1970 L46 new carb today, question...

here the advance routing

[Joe L.]

Re: 1970 L46 new carb today, question...

The vacuum connects to the TCS switch front port on the passenger side. There should be a metal tube between two pieces of vacuum hose. The back side of the TCS switch also has at least one vacuum hose that connects to a vacuum nipple at the top back of the carb. I took mine apart or I would take pictures.

If you have a Vette Vues Fact Book, there is an excellent picture on the back inside cover showing the correct routing. If memory serves me it is also shown in the assembly manual.

Hope that helps.


Bill

Bill-----


Yes, I should have said vacuum advance VACUUM SOURCE line connects to the vacuum fitting on the upper front passenger side of the carb float bowl. From there, the vacuum line does connect to the TCS switch and the TCS switch to the distributor vacuum control. My assumption was that the question only involved where the VACUUM SOURCE line was to be connected to the carb and not the complete, upstream vacuum system but that may have been an incorrect assumption.

[Greg H.]

Re: 1970 L46 new carb today, question...

Dennis,
Could you please post where you sourced your vacuum tubing? Also, I received my reproduction hard line today. I am concerned about the diameter of the crimped end. It is not as large as the tube coming out of the carburetor. Hopefully it will seal. I know you put a lot of research and effort into having the tube produced. Do you have a pic of the tube you have before mounting it ( not the original but the repro). Or do you have the proper diameter measurement for the crimped end?
Thanks,
Greg

[Dennis D.]

Re: 1970 L46 new carb today, question...

Dennis,
Could you please post where you sourced your vacuum tubing? Also, I received my reproduction hard line today. I am concerned about the diameter of the crimped end. It is not as large as the tube coming out of the carburetor. Hopefully it will seal. I know you put a lot of research and effort into having the tube produced. Do you have a pic of the tube you have before mounting it ( not the original but the repro). Or do you have the proper diameter measurement for the crimped end?
Thanks,
Greg

Greg not sure I understand. What is the "hard line" and "reproduction tube you refer to?
There's a short rubber hose attached to the carb vacuum fitting. The advance tube connects to the other end of that rubber tube. Then it "U's back to another short rubber hose that connects it's other end to the TCS solenoid.(as in the photo I posted )

I have the repro'd tube on my car now and it seals fine. The rubber hose off the carb should have a small inner diameter. I'll try to post a pic of both for you. BTW Classic Tube for the piece

[Greg H.]

Re: 1970 L46 new carb today, question...

Dennis,
I bought the reproduction steel vacuum tube you worked with Classic Tube to produce. This is the one with the single crimped end, and the two bends which bring it back toward the TCS valve. The crimped end that goes into the rubber tubing then to the carburetor seems to be a smaller diameter than the tube coming out of the carb. So I'd like to know if your metal tube is also slightly smaller OD at the crimp compared to the metal carburetor tube.

Also, i was wondering where you bought your striped vacuum hose material which connects to both ends of the special bent steel tube from Classic Tube.

Thanks,
Greg

[Terry M.]

Re: 1970 L46 new carb today, question...

The metal tube should be smaller than the carburetor tube. The tube you just bought fits into the carburetor tube and the rubber hose fits over all of it. The actual vacuum seal is the rubber hose, so the metal tubes may fit together loosely. There is a drawing in the front pages (first 10 or so) of every AIM with a cut-away drawing of this type of connection, showing the position of the rubber hose and the metal tubing. The vacuum line that goes to automatic transmissions used the same kind of connection at the back of the intake manifold for years and years on all types of GM vehicles.