Datsun Roadster Forum-311s.org

Hello Gang,

Can anyone tell me how to replace the vacuum tube that comes out of the rear carb on my 1600? The tube snapped off at the base.

I have another set of SU's for parts but I can't seem to get that pesky little tube out.

Thanks,
Ron

Ron:
I had the same thing happen to me and I ended up drilling it out using a drill press and small increments of drill sizes until the old one was removed.
The old one seemed to be press fitted in.
I went down to the local u-pick wrecker and obtained an inexpensive old carb base with a similiar tube size and broke the alum around the tube to get it out.
I drill press opened the vacuum tube hole to tightly fit the new tube and lightly tappped the insertion side of the tube diameter to make to ever so slightly oval.
I applied a some liquid thread loctite a distance from the insertion end and press fitted the tube back into the hole.
Then I put a small amount of loctite around the base of the tube.
Worked for me.

Hope this helps
Ray B.

Ray,

Wow sounds like a mess. When you finally removed it what is under the fitting? How is the vacuum controlled?

It seemed pressed in? Do you think if I took some vice grips too it it might wriggle out eventually?

Thanks,
Ron

Ron:
Mine was broken off flush to the casting, so I had to go that route.
You might be able to work the tube out with grips, but be careful not to break if off flush like mine was, and use a little lube on it to help it on the way out.
There is a smaller hole at the end of the tube hole which goes straight up thru the casting into the venturi, exiting right against the closed butterfly face( upstream side) .

I believe as the butterfly is opened a low pressure area is created in the venture throat as the air flow passes thru it and the vacuum hole is in the area of low pressure.
The vacuum line goes to vacuum advance of your distributor where its separated from the higher atmospheric pressure by using a rubber diaphram. Your advance plate lever is attached to the diaphram.

High pressure always trys to replace a low pressure area , so when the vacuum is created in the venturi the high pressure pushes against the diaphram to try and get to the low pressure vacuum side of things, thus moving the distributor plate in the process.

If the diaphram wears out or gets a leak in it the higher pressure will have a direct path to the low pressure area and the vacuum advance timing will not work as intended and you are left with only the centrifical advance for adjusting your timing while driving.

Now I'm confused ...What was the question?

Happy motoring.

Ray B.

Ray,
Well in the process of trying to get it out it broke off flush. So I drilled it out.
The replacement came out in one piece, so I had to use some sealer to get it in the new spot.
Checked the vacuum canister and it seems to be functional, (although extremely rusty) no leaks.
As I was checking the tab to the points plate, I noticed the rotor had play in it. Off to Autozone where they had one cap/rotor set left in stock.
Put it all together and when it fired it seemed to idle much higher rpm and smoother. I think that's good, lowered the idle and it slowed.

Does fixing the Roadster remind anyone of never-ending connect the dots? Just when you think you've got one thing fixed, another pops up just ahead.

Well it runs and my motoring is very happy.
Ron