1970 L46 new carb today, question...

[Dennis D.]

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

Greg I believe Dr Rebuild sell the hoses.

The advance tube fits loosely, but seals quite well. Have no problems. The diameter of the advance tube is the same as the diameter of the metal tube on the front of the TCS solenoid. The hose there is the same diameter as the one from the carb to advance tube.(see my photo obove in the post)

The hose does expand enough to fit that larger diameter tube on the carb. In fact, took a real effort to get the hose off the carb.

[Greg H.]

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

Here is a picture of mine with the tube installed. Thanks to all for your help getting it together. The car is running pretty good with it. I don't notice a difference in 3rd or 4th gear, but I really don't have much time behind the wheel with this new carb installed.

Anyway, one more question for Dennis or the others with this L46 setup: Do you have any interference with the air cleaner base? Mine is definitely touching the new tube and pressing it downward. It's all under a little stress when clamped down. Is it just a matter of adjusting the orientation of the tube? My tube actually looks a bit longer than Dennis'.
Thanks,
Greg

[Dennis D.]

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

Greg. Looks good but a bit long to me. Your photo is of the same view as the one I posted. Makes for good reference pionts. Your tube seems to have more length coming out of the carbs hose, which is why I assume you have a longer hose at the TCS solenoid to make that connection. What part number is your tube? Here's a photo of my from classic



This is the original measurements I used after confirming with several members who were kind enough to check for me. They all were the same, within reason. Also the original I sent classic to copy was the same



Also don't know if you have this or not, but this explains the TCS system. A simple way to test if it function properly is to start the car and with the clutch in, shift to 3rd 0r 4th gear. (continue to hold the clutch in obviously) There should be a noticable idle increase in either 3rd or 4th gear.

[John H.]

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

Also don't know if you have this or not, but this explains the TCS system. A simple way to test if it function properly is to start the car and with the clutch in, shift to 3rd 0r 4th gear. (continue to hold the clutch in obviously) There should be a noticable idle increase in either 3rd or 4th gear.

I'd just add that for this check, the engine needs to be warmed up so the solenoid responds to the switch at the transmission 3-4 lever; if it's started from cold, the cold override will activate the solenoid and the 3-4 switch will have no effect until the coolant warms up and the cold override drops out.

[Terry M.]

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

1970 is 3-rd and 4th gear. 1971 and newer is 4th gear only. That, of course, checks that the transmission is properly configured for the year car it is installed in. There is a time delay in some years with some engines. I worked through all that and the years and transmissions are in the 1970-72 Operations and PV Manual.

[Greg H.]

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

Dennis,
The part number I requested was CV01004-OE. Mine seems to match your dimensions. (There is also a slight bend in the vertical portion between the two curves, but this does not impact the current problem). So perhaps the tube coming from my carburetor is extended to far out?

Now, in one of your notes above, you say the crimped end fits into the carburetor tube. Mine butts up against the carb tube, all covered by the tubing.

Thanks also for the TCS test notes. I'll worry about that later but it is in mind as I have a background goal of achieving PV.

[Dennis D.]

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

Dennis,
The part number I requested was CV01004-OE. Mine seems to match your dimensions. (There is also a slight bend in the vertical portion between the two curves, but this does not impact the current problem). So perhaps the tube coming from my carburetor is extended to far out?

Now, in one of your notes above, you say the crimped end fits into the carburetor tube. Mine butts up against the carb tube, all covered by the tubing.

Thanks also for the TCS test notes. I'll worry about that later but it is in mind as I have a background goal of achieving PV.

Greg....
Thats the part number Tom gave me for original steel.

There are compound bends. The one you speak of is just right to get under the fuel line.

I suspect that tube on your carb may be the problem. Just doesn't look right to me.

The crimped end does not go into the metal tube on the carb. Sorry if I missled you there. In fact I don't think the crimp end is that close to the carb metal tube.

I have no interference with my air cleaner. Going to take another pic. I'll measure that carb tube length while I'm there.

[Dennis D.]

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

a few pics

[Greg H.]

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

Thanks for the follow up, Dennis. Yes, that must be the issue. The tube on my carb is about 7/8 inch so it's just long enough to cause interference with the air cleaner base. I'll have to yank it out and cut it down. Good to see more pics. I could use a complete set of those close ups!
Thanks again,
Greg

[Terry M.]

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

Dennis,
The fitting on the end that goes to the pipe on the carburetor looks unlike what I believe the originals are. I understand that end can't be seen during judging, but the functionality of the tube may be compromised if the tube does not have a small diameter end that fits into the pipe on the carburetor. I believe the tube should fit into the pipe on the carburetor just like the vacuum line to the automatic transmission fitts into the vacuum fitting on the intake manifold.

I suspect whoever is making them needs a tool something like this.

http://www.aircraft-tool.com/shop/dbpics/large/AP145.jpg

There may not be enough margin or volume in the tube to justify the cost of these tools, and at best only one is needed -- not the whole set. Of course if the tube is smaller than 1/4-inch this tool will not work either. That said perhaps something can be worked out to make the tube so that the carburetor end will be more secure.

I'm not sure if that has anything to do with Greg's problem or if it is a different issue.

[Dennis D.]

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

Dennis,
The fitting on the end that goes to the pipe on the carburetor looks unlike what I believe the originals are. I understand that end can't be seen during judging, but the functionality of the tube may be compromised if the tube does not have a small diameter end that fits into the pipe on the carburetor. I believe the tube should fit into the pipe on the carburetor just like the vacuum line to the automatic transmission fitts into the vacuum fitting on the intake manifold.

I suspect whoever is making them needs a tool something like this.

http://www.aircraft-tool.com/shop/dbpics/large/AP145.jpg

There may not be enough margin or volume in the tube to justify the cost of these tools, and at best only one is needed -- not the whole set. Of course if the tube is smaller than 1/4-inch this tool will not work either. That said perhaps something can be worked out to make the tube so that the carburetor end will be more secure.

I'm not sure if that has anything to do with Greg's problem or if it is a different issue.

Terry...

Interesting tool. It didn't accure to me the advance tube would fit into the carb tube. Although looking at my original sample it does make sense.



For some reason the fabricator of the tube does not have the stock or ability to make that double bump.(they don't refer to them as flares). I had him duplicate the tube for it's unique compound bends and retain the computer pattern. I have had leads for the double bump stock, with a couple of more to check out. The plan is to sent the fabricator the stock and have it available. The saga continues.....

[Terry M.]

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

The idea is that the tube is mechanically located inside the pipe on the carburetor. The rubber hose only seals the vacuum, and provides little or no mechanical location, but does keep the tube from pulling out of the pipe. In judging I often see the tube miss-located mostly because the nature of the connection is not well understood. One can easily wind up with a vacuum leak if the tube and hose are not located properly.

In the front pages of each of the AIMs is a picture that shows this kind of connection and the location of the hose. The first bump keeps the tube from penetrating too far into the pipe, and the second bump provides a location for the rubber hose -- If I recall the image correctly.

It is not a terribly sophisticated connection -- nothing like modern cars -- but it has worked well for a long time.

Years ago Chevrolet used to sell the vacuum tube to the Turbo Hydromantic transmission as a straight tube (almost three feet long) with a pre-formed end like we are looking at. I suspect that tube is a larger diameter, and probably long since discontinued -- but it might be worth looking into. I don't think I have one on hand. I seem to remember using the last one I had on some beater years ago.

[David L.]

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

I made three 3965581 spark pipes (1970 Corvette AIM, UPC 6, sheet C1) by reforming 3 other much longer original GM spark pipes that I bought at swap meets using dimensions from a member of the Nasty Z28 web site who owns a 1970 Camaro SS350 (L48 option, 300 HP eng.). The 70 Camaro SS350 uses the same 3965581 spark pipe (1970 Camaro AIM, UPC L48, sheet A3).

The three photos on the right are of an original 3965581 spark tube from the Nasty Z28 web site.

Corvette Central sells a reproduction spark tube for 68-69 Corvettes with "double fittings" that can be reformed to make a 3965581 spark tube. The two fittings on the reproduction tube are a bit thicker then the original GM spark tube fittings.

Dave

[Alan S.]

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

Hi,
I read this thread and the discussion of the ' bumps' on the tube with interest. (I don't remember it from 4 years ago.)
All along I've always thought the bumps were there to allow 2 different size hoses to attached the same tube. The smaller hose pushed on the tube up to the bumps and a larger hose pushed over the bumps.
Is this another use for the bumps in addition to the 'mechanical location' Terry describes?
These pictures are the original tube and hoses from my 71 350/270. Note the larger diameter hose at the CEC solenoid end required by the size of it's nipple, and the small hose at the distributor advance end.
Just curious?!
Regards,
Alan

[Terry M.]

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

This is exactly the "mechanical connection" I attempted to describe years ago. If you look at the first few pages of your AIM it will show a cut-away view of how these "bumps" on the metal tubes are supposed to work. That picture is worth quite a few of my feeble words.

The metal tube slides into the hole on the fixed unit (the solenoid in the illustration you provide, but it could also be into the intake vacuum fitting) up to the first bump and the short rubber hose covers the fixed unit and over the second bump on the metal tube. So actually the short rubber hose is simply a final seal for the vacuum and a locator for the metal pipe to hold it into the hole in the fixed unit. Too often I see the metal pipe mis-aligned with the fixed unit and the short rubber hose providing the path for the vacuum. That is guaranteed to quickly deteriorate the short rubber hose and then create a vacuum leak and subsequent poor engine performance.