1 hour ago, Bruce Palmer said:

With the piston in and dome in place start running the screws down unformly while lifting the piston with a finger and allowing it to drop. If you are cattywompis and the needle is binding, back the screws off a smidge and nurse the dome sideways until it  (the needle) drops freely. Continue until screws are tight and the needle drops cleanly into the orifice...... Do not under penalty of death, adjust your floats during this operation...... Now that's funny I don't care who you are!!

Thanks for your kind advice. I might have screwed the float level either on the front or rear carb as the engine still backfires at the carbs intakes at 3.5 turns clockwise. I am not certain of the history of the needle valves and maybe they are not in the correct working order. 

Doesn't seem like needle valves would be causing the problem -- there are adjustments built into the carbs that can compensate for minor variance. Nice to have fresh parts for a thorough rebuild, but if the needle action feels smooth and even for both, cross them off the list and go back to the usual suspects.

Why is it still backfiring through the intake after 3.5 turns clockwise

Timing? Advance a little and see how she responds

Edited February 24, 20187 yr by David F

1 hour ago, David F said:

Timing? Advance a little and see how she responds

Ill try that tomorrow. 4 hours of setting front and rear carb floats to the correct fuel level. If i bend the tangs more fuel will spill from the lid air inlets.

I experienced ocassional fuel bowl overflow.  I attributed the issue to less than optimal float tang geometry.  The modern valve stem design does not glide on the tang as easily as the original design as has been said in this thread previously.  My solution was to remove the sealing washers from the base of the fuel valve body to lid/inlet port.   Once I did that, tang to valve geometry is improved and issue went away.

Well i set them at the level shown. All plugs are fouled and car misfires as i start to accelerate. I'll replace all spark plugs with a new set and test the car to see if the misfire and stumbling goes away.

On 2/16/2018 at 8:21 AM, David F said:

Not sure what you are talking about, so I think not.  needles look like any other to me.

You answered my question from earlier, thanks.

47 minutes ago, David F said:

I experienced ocassional fuel bowl overflow.  I attributed the issue to less than optimal float tang geometry.  The modern valve stem design does not glide on the tang as easily as the original design as has been said in this thread previously.  My solution was to remove the sealing washers from the base of the fuel valve body to lid/inlet port.   Once I did that, tang to valve geometry is improved and issue went away.

 

Im reall concerned on the difference on the reading of the psi of the former pump vs this new one which is the same model.  My mechanic did installed a  restrictor after the fuel filter before the carbs. Should i remove it? Its the bronze color one between the clips.

Edited February 25, 20187 yr by jalexquijano

That's a reducer not a restrictor, for a step down on hose size, it won't affect the PSI.

Edited February 25, 20187 yr by siteunseen

1 hour ago, siteunseen said:

That's a reducer not a restrictor, for a step down on hose size, it won't affect the PSI.

Are these fuel levels on the front and rear carb floats okay?

1 hour ago, jalexquijano said:

Are these fuel levels on the front and rear carb floats okay?

I know you are frustrated, but I'm not sure anyone is going to be able (or willing) to say your fuel levels are okay based on a picture of the tubing fluid level.

I personally think you should give up on the sight glass method you are using, and try something else. or at least check your levels with this method and see if you are way off base.

 

 

The problem is this diagram shows the level with the float sitting in the fuel, which would bring it further up than it would be when the lid is off.

This is why the method i used of 10 turns down of the nozzle checks this... as that would equal the 1cm down shown on the right side.  Use a flashlight to check the fluids position on top of the nozzle.

 

See these references:

http://datsunzgarage.com/engine/index.htm

Quote

HOWEVER: Even though adjusting the floatbowl levels to 23mm down is a factory setting, it doesn't guarantee that the fuel levels in the carbs are the same.

THE TRICK: 
I did some measuring with a straightedge and found that on my 4-screw SUs a 23mm fuel level in the float bowl corresponds to exactly 1 centimeter (10 millimeters) below the fuel nozzle "ledge" in the carb. But how do you see to measure fuel 1 centimeter down inside the fuel ozzle? See below. 

- Remove the dome and main piston from each carb so you can look down the tip of both fuel nozzles. 
- Screw each mixture nut exactly 10 turns down from fully up. Each full turn drops the nozzle tip 1 mm, so 10 turns puts the tip of the fuel nozzle 10 mm (1cm) down....which happens to be the 23mm float bowl level. 
- Then look down the tip of each fuel nozzle and adjust each float to set the gas level at the fuel nozzle tip. 

I ended up taking mine to 9 turns down and set the fuel at the meniscus of the tip. Then when I went to 10 turns the fuel was exactly at the tip. A bit of a juggling act but after a few minutes you will get the hang of it. When you get them to match it's a great feeling.

NOTE #1: if your mixture nut won't go down more than a few turns, it's because the factory "stopper" next to the nut is still in place. Unless originality is a concern, you can permenantly remove both stoppers from the bottom of the carb. 

NOTE#2: if the fuel level is too high and overflows the nozzle tip, you will need to drain each float bowl a bit before starting again.

The result was a lower, more solid idle and less choke needed at startup. I get no stumbling off idle and part-throttle acceleration is smoother, acceleration more powerful. Cruising on the interstate requires a lighter touch on the accelerator. Interesting. 

 

Edited February 25, 20187 yr by DaveR