Datsun Roadster Forum-311s.org

Purchashed a 1967.5 1600 1.5 years back
Love the car but continue to have over loading of the carbs after driving an hour or so. Sit at stop light and carbs overload..Once you get going and get up to full speed the carbs setting back down
Any suggestions

Welcome to the site! I would suggest you spend some time reviewing the carb tuning info in the wiki so you understand the system you're working with, but it sounds like they are set a bit rich at idle. There is a dial that is at the center of the carb body underneath that will lean the mixture by screwing it upwards. Try a 1/4 turn on each carb and see if that helps. Also, make sure the engine is in a good state of tune with good plugs, points, cap/rotor, condenser, plug wires and valve adjustment.

By overloading, do you mean the mixture richens at idle and the car "loads up" so that you have to rev the engien to keep it from gradually sopping?
Or do you mean gas runs out the car overflows?
Or, does it begin to miss at idle and eventually die?

How about a description of what it's doing? When you first start it (cold) does it take much choke? Does it idle well cold with no choke?
So, now you drove over to the liquor store across town and you're on yhour way home...engien at operating temp. Car is sitting at a red light. What's it doing? Will is happily sit and idle? If not, what does it do?

Dan

Been there with my early 67.
Yes. Do everything Greg said.
Then call up Z Therapy, buy some of their beautiful carbs and drive happy.

Be sure you have plastic floats. Brass floats can start to get pin holes, then start to sink, a little or alot, thus not shutting off the gas , a little or a lot....
Shake them to listen for gas, or boil them to watch for air bubbles.
Several threads on the subject.
Linda
Check float valves for sticking or inspect for wear...not able to function correctly

Not overheating too?

You do not want the fuel level any higher than carb deck. Are you familiar with the old water level check using a clear plastic hose? This will work using a aquarium hose connected to float chamber and bending into a U shape.

Reviving this thread as it is very similar to my problem with my 67 1/2 1600. Symptoms are the same as described above so I am going to Attempt to lean the rear carb as a check of the spark plugs shows both rear plugs very dark. Firstly, I AM NOT an experienced mechanic but am learning as I go, so please excuse my obvious ignorance. Wiki explains how to test and adjust fuel mixture, and I have watched several videos on the procedure. Where I am confused is that all tutorials refer to an adjustment "NUT" and my car seems to have an adjustment thumbscrew. (see pic). All of the exploded views ive seen show an adjustment nut, i have not seen any with the thumbscrew type. Can I assume that this is one of the SU versions and the function is the same?

The thumbscrew is a stop on the 68 and later cars.

spl310, So if thats the case, I have to assume these are not the original carbs for my 67 1/2 ? And does it perform the same function as far as being an adjustment for the fuel mixture as the adjustment "nut" on the earlier versions?

I don't see the thumbscrew stop, so they could be original

Im guessing that I did not pose my question correctly. On all the exploded views ive looked at, the assembly has a lock nut at the top of the assembly, and an adjustment nut at the lower end. Mine does not have an adjustment "nut "on the bottom, Instead, it has what ive reffered to as a thumbscrew at the bottom .It is round and resembles the fasteners that hold the dash toggle switches in place on the early models. Im assuming that the "thumbscrew" is the adjustment mechanism?

Ok. The lock nut at the top is what us used to center the jet on the needle. The thumbscrew looking nut on the bottom is the adjustment. There is actually a thumbscrew that is a stop on later carbs - that is what I thought you were referring to. Yes, it is the adjustment.

Thank you spl310. Not the first time your knowledge has helped me. I feel comfortable taking on simple tasks such as brakes or parts replacement, but carbs are not something ive had any experience with. (yet) Although they are relatively simple on our cars, there is potential for doing more harm than good. Beings im 800 miles from a qualified roadster tech, i'm forced to stop being a lazy a$$ and start wrenching more on my car. Its both interesting and terrifying.

Happy to help Bajaroadster! These are extremely simple carburetors. No transition ports to deal with, no tiny passages to plug, just a few moving parts. They intimidate people because they are not familiar looking, but they are really not bad to deal with. I need to adjust the carbs on my 2000, but I'm not home enough to get it done. Frustrating.