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Round top carb dampening Rod


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#1 OSU-zanatic

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Posted 3 weeks ago

Hey everyone,
The car is a 1972 240z with an L28 running 4 screw round top carbs.
So I have been trying to get my car to run right for awhile recently found and fixed vacuum leaks including replacing the master cylinder and brake booster. I replaced the starter with one from a 1980 280zx, also replace the ignition coil with a 3ohm flamethrower and changed to a pertronic electronic ignition. I removed all egr and plugged the ports on the balance tube.
My main question has to do with the damper rod for the carbs. I have watched the "Just SUs" DVD and plan to watch it again once I get home. The piston will not drop at the same rate, I have taken them apart and plugged the air ports the pistons will drop at the same rate but once I assemble them and Fill them with ATF one drops slower than the other. The reason this is is because the cylinder on the damper rods are different size, I don't have a micrometer to measure the difference but can visually tell and feel they are different sizes. I seem to recall it being mentioned in the DVD that he has seen two different sizes but shouldn't the car have the same size dampers to let the pistons fall in unison?

#2 Neverdone

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Posted 3 weeks ago

If you're going to school at OSU, don't you have access to the shop under Rodgers hall? They have every single tool there is pretty much. Can you borrow a micrometer?



#3 OSU-zanatic

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Posted 3 weeks ago

My car is in Santa Cruz, California, I only get to see her for a couple weeks every year and not going to bring it up until I'm confident in its ability to get me around

#4 OSU-zanatic

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Posted 3 weeks ago

I know a few machine shops that will measure it for me. Should I had them machine the larger one down to the size of the smaller cylinder?

#5 Miles

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Posted 3 weeks ago


“Life is like arriving late for a movie, having to figure out what was going on without bothering everybody with a lot of questions, and then being unexpectedly called away before you find out how it ends.”    -Joseph Campbell


#6 OSU-zanatic

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Posted 2 weeks ago

Miles, 

 I have dine this and the rate if the same this is what I meant in my original post when I said I plugged the air ports and the pistons fell at the same rate. Unfortunately I was unable to work on my car when I got home, I came down with guillain barre syndrome and have been in the hospital for the last 5 days, moving to rehab today fr about 10-14 days and taking this term off school for physical therapy. So the good news about all this is that I will be able to devote a lot of time to my 240 in the next few months.

Again the pistons drop at the same rate when I do this test but once I put them on the car, fill them with fluid, and replace my dampening rods they no longer fall at the same rate, the piston with the smaller dampening rod cylinder falls much quicker than the larger on, I have swapped the rods and this stays consistent. I have an efi setup sitting on the side but missing a couple things for it like the larger fuel lines and the refi relay, I would rather get the car running with my carbs before I think of swapping.

Should I take the dampening rod cylinder and have it machined down to the same size as the smaller one?



#7 Miles

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Posted 2 weeks ago

Miles, 

 I have dine this and the rate if the same this is what I meant in my original post when I said I plugged the air ports and the pistons fell at the same rate. Unfortunately I was unable to work on my car when I got home, I came down with guillain barre syndrome and have been in the hospital for the last 5 days, moving to rehab today fr about 10-14 days and taking this term off school for physical therapy. So the good news about all this is that I will be able to devote a lot of time to my 240 in the next few months.

Again the pistons drop at the same rate when I do this test but once I put them on the car, fill them with fluid, and replace my dampening rods they no longer fall at the same rate, the piston with the smaller dampening rod cylinder falls much quicker than the larger on, I have swapped the rods and this stays consistent. I have an efi setup sitting on the side but missing a couple things for it like the larger fuel lines and the refi relay, I would rather get the car running with my carbs before I think of swapping.

Should I take the dampening rod cylinder and have it machined down to the same size as the smaller one?

 

Do you know what the dampening rod does?


“Life is like arriving late for a movie, having to figure out what was going on without bothering everybody with a lot of questions, and then being unexpectedly called away before you find out how it ends.”    -Joseph Campbell


#8 OSU-zanatic

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Posted 2 weeks ago

Looking at the design, it should control the movement speed of the piston determined by the diameter of the cylinder on the dampening rod.
Take the cylinder off the dampening rod and your piston will drop with almost no resistance as if you don't have one in. so one cylinder having a larger diameter than another will cause the position to drop slower. Correct me if I'm wrong.
Trying to get a family member to bring me my just SU DVD so I can't watch it on repeat while in rehab.
Has anyone seen this where they have one dampening rod cylinder bigger than the other?




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