Datsun Roadster Forum-311s.org

Hi ! I hope someone out there who can help me with a question I have about my 1600 SU carburetors ! Is there an explanmation as to why my 2 carburetors nozzels travel from the closed position to their stops are totally different ? The back carburetor only opens about half as much the front one is there an adjustment I'm missing ? I'm about to pull my hair out and I don't have much anyway ! If someone can tell what I need to do if anything to correct this it would be deeply appreciated !! THANKS AGAIN !! DON !

do you have the nozzles (under carb) set the same distance? What about the piston in the dome? Are they the same?

Alexi

If you are referring to the mixture screw on the bottom of the carb, there is a secondary stopper on some of the (later smog?) carbs. This stopper can be screwed up or down to restrict the movement of the mixture screw. It is under the carb closer to the engine. Maybe one of your's is tightened.

According to my manual, some carbs were not to be adjusted do to emissions requirements, so this could be the case with yours.
Ron

THANKS FOR THE HELP ! The nozzles are set the same amount of turns and the pistons are the same ! These are non smog carburetors ! The position of the ears on the spring loaded rotating shaft are not the same about 1/2 inch difference ! The shaft is what lowers the nozzle for the choke ! Does this make any difference that one travels or drops about 1/2 inch and the other about 1 inch for some reason ? I'm puzzzled and need some expert advise as to this problem !!! THANKS AGAIN FOR ANY HELP ! I'm beginning to get frustrated because this car has been one problem after another and no one around here wants to work on it so I'm stuck trying to fix it myself !!

PROUD ROADSTER OWNER wrote:I'm beginning to get frustrated because this car has been one problem after another and no one around here wants to work on it so I'm stuck trying to fix it myself !!

I suggest the "Just SU" video from ztherapy. Learn as much as you can. Hopfully you'll aslo find a fellow roadsterite in your area. If you lived near me (which you don't) I'd come by to help out. Anyone in Il. to help a fellow?

And here's a great link for more SU info:

http://www.jetlink.net/~okayfine/sutech.html

"...stuck trying to fix it myself!" Actually, I find working on the roadster to be quite therapeutic. The more I get into it, the more I discover that it's actually a fairly simple beastie.

I was raised to fix-it-myself, which is extremely difficult these days. Heck, I just paid $3000 to have the tranny rebuilt in our Chrysler Concorde.

After reading the stuff on this site and on the mail list, I'll do my own roadster tranny if it becomes necessary.

There's a lot of pride to be had saying "I did it myself!" Enjoy.

If one spring is compressed more than the other that would change the rate of the spring. SU's need to be setup identical. Either source the correct parts to make them as such or find carbs that match. Have you checked the flow of the carbs? Does one "suck" more than the other?

Alexi

Man..I hate it when the word "suck" is used to describe a su carb air flow.
Can we just say "the sound of the air entering each carb should sound the same if they are balanced ".
(I.E.) same sucking sound.

Ray B.

Don, this is what I do with problem SU's when I get them in my shop.

First, I start by pulling the tops of each carb apart and setting the pieces out on the bench (keeping the parts for each carb separate) and cleaning each piece thoroughly. Inspect to make sure that the needles are positioned at the same height on both pistons, compare the length of the damper spring.

Secondly, I disconnect the choke cables to get them out of the way and also to let the mechanisms be free on the carb. Also, disconnect the throttle linkage (the ones with plastic ball ends) this will allow you to operate each carb individually.

Third, I run the jet nozzles all the way flush with floor of the carb. You may need push up on the nozzle to help them go flush, if they just won't go flush, you may need to disconnect the nozzle from the arm that comes down at the bottom of the nozzle (don't drop the nozzle and don't lose the tiny bushing that the arm pivots on.)

At this point, I start looking at the linkages, checking for anything bent, missing, corroded, binding. There is a return spring for the choke linkage, make sure it's still intact and positioned correctly. Basically I look for anything different between the front and rear carbs.

By going thru these steps and being very meticulous and anal, the problem will usually jump out at you. This usually takes me anywhere from 1 to 3 hours, depending on how elusive the problem is. So set aside a chunk of time that you can be undisturbed so you can really delve into the project.

I hope this helps you out. Try to have fun with it!

Mark