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hatepotholez

Engine only runs with starter fluid

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Well there's no guarantee that those alignment nubbies will line up with your replacement suction chamber, but certainly TRY them first before you remove them. You might get lucky and have a temporary local relaxation of Murphy's Law. Doesn't hurt to try first.

When you think about the geometry, you really need to be very close. You're trying to stick a 95 thousandths diameter pin into a 100 thousandths diameter hole and (in a perfect world) have it not contact anywhere around the perimeter. They couldn't hold the necessary tolerances at the factory, so they resorted to characterizing every carb instead by fixturing them and using "cast in place" alignment pins instead.

And if you do cut the alignment pins off, remember that you're going to have to realign those suction chambers each and every time you ever take them off again in the future. (Same goes for you Cliff!)

 

 

 

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4 hours ago, siteunseen said:

I honestly don't know, I watched the DVD a couple of times then rebuilt the two carbs.  They were original to the car and it had been sitting for 10 years.  During the rebuilding I found the nozzles weren't dropping down and the float chambers were crudded up, the float valves were sticking too.  Now they're nice and shiny and work like new (I'm guessing-I was 3 years old when they were new). :)

LOL which reminds me, I have to watch the SU DVD in it's entirety.

4 hours ago, Captain Obvious said:

Well there's no guarantee that those alignment nubbies will line up with your replacement suction chamber, but certainly TRY them first before you remove them. You might get lucky and have a temporary local relaxation of Murphy's Law. Doesn't hurt to try first.

When you think about the geometry, you really need to be very close. You're trying to stick a 95 thousandths diameter pin into a 100 thousandths diameter hole and (in a perfect world) have it not contact anywhere around the perimeter. They couldn't hold the necessary tolerances at the factory, so they resorted to characterizing every carb instead by fixturing them and using "cast in place" alignment pins instead.

And if you do cut the alignment pins off, remember that you're going to have to realign those suction chambers each and every time you ever take them off again in the future. (Same goes for you Cliff!)

 

 

 

This is true. Hopefully the replacement parts work. 

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Best of luck with the replacement parts. Hope that fixes your carb issues.

While you're waiting for parts to arrive, can you take a couple close-up shots of the suction chambers and the top of the carb bodies where the nubbies stick up? I've never seen those alignment pins on anything other than the flat top carbs. Sounds like they started that process in 72 and went on like that through 74.

So your carbs don't have any provision for aligning the nozzle underneath? Sounds like (unlike the previous years) your nozzle position is fixed and the suction chamber is (was) the movable entity?

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I had my spares down today and was going to post some pics!

I'll do it in the a.m.

Mine are 3 screws with the nubbies on the front 2 screws.  The rear screw has nothing. The way the nubbies are positioned, one side is above the screw hole and the other side it's below. The suction chamber can only go on one way. If you slightly tighten the screws, get the piston dropping smoothly then tighten them down it's super simple.

The nozzles have to have their angled "leg" pointing to the float chamber and that's it. 

I won't disagree with you but the nubbies are no big deal on the 3 screws I have. They're all crumbly anyway.

I'm too comfortable to go downstairs at the moment but will in the morning for pictures. 

I can't understand why his are fine without screws but bind with screws? I'm too frugal to buy new parts but everybody's not like me and you. LOL

Goodnight Sir.

 

 

 

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11 hours ago, Captain Obvious said:

Best of luck with the replacement parts. Hope that fixes your carb issues.

While you're waiting for parts to arrive, can you take a couple close-up shots of the suction chambers and the top of the carb bodies where the nubbies stick up? I've never seen those alignment pins on anything other than the flat top carbs. Sounds like they started that process in 72 and went on like that through 74.

So your carbs don't have any provision for aligning the nozzle underneath? Sounds like (unlike the previous years) your nozzle position is fixed and the suction chamber is (was) the movable entity?

Thanks. I will take some photos on Sunday. I haven't actually seen the bottom of the carbs as they are installed. The nozzle goes up and down into a bronze tube.

10 hours ago, siteunseen said:

I had my spares down today and was going to post some pics!

I'll do it in the a.m.

Mine are 3 screws with the nubbies on the front 2 screws.  The rear screw has nothing. The way the nubbies are positioned, one side is above the screw hole and the other side it's below. The suction chamber can only go on one way. If you slightly tighten the screws, get the piston dropping smoothly then tighten them down it's super simple.

The nozzles have to have their angled "leg" pointing to the float chamber and that's it. 

I won't disagree with you but the nubbies are no big deal on the 3 screws I have. They're all crumbly anyway.

I'm too comfortable to go downstairs at the moment but will in the morning for pictures. 

I can't understand why his are fine without screws but bind with screws? I'm too frugal to buy new parts but everybody's not like me and you. LOL

Goodnight Sir.

 

 

 

I'm not sure either. Honestly I don't think it's from dropping it and was probably an issue from before I even purchased the car. This was another owners project that I took on so I am not sure if the carbs were rebuilt thoroughly. 

I agree on being frugal, I have two projects and do not like spending money if I have to, unfortunately this is something I don't think I could avoid as I really do not want to remove those alignment tabs until I have tried all avenues. 

 

 

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Without seeing the parts myself, I can't tell you where the interference is, but dropping it sure doesn't help. It doesn't have to be bent much. A thousandth in the wrong spot would probably be enough to cause the binding you're experiencing. Think about it this way... The only "seal" between the upper side and the lower side of that suction piston is the close fitting (but non-contact) dimensions of the OD of the piston in the ID of the suction chamber. Doesn't take much distortion to cause interference. Out of round chamber. Out of round piston. Bent damper tube, Bent needle. Bent mounting tab on chamber.

The reason the binding goes away with the screws not installed is that the chamber and piston can squirm around just enough in whatever direction it wants to in order to move without binding. Doesn't have to be a lot of interference, and doesn't have to be a lot of squirm.

You'll figure it out, and hopefully it's as easy as swapping out the piston and chamber. Maybe you'll have to remove the nubbies, maybe you'll get lucky.

As for the alignment pins.... You really only need two alignment pins to establish repeatable positioning. That's why a third pin on the rear screw is unnecessary. On the flat tops, the nubbies are actually cone shaped and that shape does a better job of establishing position than a straight sided cylinder. Are the 72's cone shaped or straight sided?

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'72 are cone shaped.  Agree with everything that Capn' Obvious stated.  On several sets that I've rebuilt I've had to knock off the nubs as well as tighten/loosen the dome screws at different intervals to get it to line up correctly to prevent interference. 

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9 minutes ago, Jarvo2 said:

'72 are cone shaped.  Agree with everything that Capn' Obvious stated.  On several sets that I've rebuilt I've had to knock off the nubs as well as tighten/loosen the dome screws at different intervals to get it to line up correctly to prevent interference. 

That's what I'm trying to say without making anybody mad or sounding like a know-it-all.  If he cut the cones off and maybe tapped the suction chamber with a rubber hammer until everything was smooth then tightened the screws?

We'll see soon enough, can't have too many Z parts. :) 

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Well I hope I'm not sounding like a know it all either as I'm certainly no carb expert. Heck, I've never even taken the 72 versions apart. Haha!
 
Jarvo, Thanks for the info on the 72 alignment cones. I've held the 72 versions and looked them over casually but they weren't mine, so as much as I wanted to, I couldn't disassemble them.
 
And I'm loony, but if I was mixing and matching parts and had binding pistons, I would heat and dig out the existing nubs, make myself an alignment tool, fixture and lock the chamber into it's new correct position, and epoxy inject myself a new set of nubbies. A little release agent on the chambers before fixturing.... Clearly overkill, and a good example of why why my projects take ten thousand times longer than normal! :D

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I love these SU carbs and have rebuilt many sets over the past couple years.  Happy to help out fellow enthusiasts!  Its fun turning beat up and worn out examples and refurbishing them.  Here are some before & after pics...

IMG_1192.thumb.JPG.b2f10b40448a684ca48e2 IMG_1239.thumb.JPG.6fdc0a6a998031ac62efa

 

 

 

 

 

 

 

 

Before4.thumb.jpg.f8a3e8e20c2e70beea821d IMG_1519.thumb.JPG.61a76c61582aeee02792c

IMG_1509.thumb.JPG.1b8cb1d65eb0f274161ed IMG_1227.thumb.JPG.bfea0d8b2a85a1b4d3d43

 

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2 hours ago, Jarvo2 said:

I love these SU carbs and have rebuilt many sets over the past couple years.  Happy to help out fellow enthusiasts!  Its fun turning beat up and worn out examples and refurbishing them.  Here are some before & after pics...

IMG_1192.thumb.JPG.b2f10b40448a684ca48e2 IMG_1239.thumb.JPG.6fdc0a6a998031ac62efa

 

 

 

 

 

 

 

 

Before4.thumb.jpg.f8a3e8e20c2e70beea821d IMG_1519.thumb.JPG.61a76c61582aeee02792c

IMG_1509.thumb.JPG.1b8cb1d65eb0f274161ed IMG_1227.thumb.JPG.bfea0d8b2a85a1b4d3d43

 

Those look beautiful.

Alot of experience on this board, which I am very grateful for. This is my first vintage vehicle i'm working on lol. Been dealing on modern vehicles my whole life. Carbs are a total new experience for me! At work all I hear i is, "I remember when I used to work on those!".

Edited by hatepotholez

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So good news and bad news. Good news is, I replaced both needles on the original pots and now both are working properly. Bad news is my rear carb keeps leaking. My plugs are extremely fouled so I'll be changing those out. Should I separate the float bowl from the carb body and then retry the float setup?

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14 minutes ago, hatepotholez said:

my rear carb keeps leaking

Leaking where? How?

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You can take those float valves apart. Remove that small clip ring at the top and pull the pin out. There's a little cone shaped at the end. Mine are grey in color. There's also a spring in there you can stretch out for a stronger closing pressure.

Clean the pin and it's seat inside the body of the valve with a can of carb cleaner. Stretch the spring and it should be like new. Or buy new ones.

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IMO, Don't remove the float bowl from the carb. body unless it's leaking at that connection. I've never seen one leak there.

 Whether your needle and seat is new or not, it's not closing all the way. I had a new one do the same thing once. I took it apart, couldn't see anything wrong, cleaned it, reassembled it and it worked fine. Never did discover the source of the problem.

To prevent the bowl gasket from "Pringling", sandwich it between sheets of wax paper and put it between two flat surfaces. I use two books.

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Just now, Mark Maras said:

IMO, Don't remove the float bowl from the carb. body unless it's leaking at that connection. I've never seen one leak there.

 Whether your needle and seat is new or not, it's not closing all the way. I had a new one do the same thing once. I took it apart, couldn't see anything wrong, cleaned it, reassembled it and it worked fine. Never did discover the source of the problem.

To prevent the bowl gasket from "Pringling", sandwich it between sheets of wax paper and put it between two flat surfaces. I use two books.

That's a good idea, I was having an issue with that gasket. It got soaked with fuel and very difficult to line up. 

Thanks!

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