How often you change these valves?

Not very often...

Fuel level in the front bowl needs to be 2 mm lower than rear bowl. that's why the ears and valves are 2 mm longer (for the later 3-screw SU's) for the front carb. Then the fuel in both nozzles will be at the same level (the main thing).

Wonder if the 4-screws also ran longer nozzles in the front? The 72 FSM doesn't mention this change - wonder if Nissan engineers were embarrassed that they got it wrong with the 4-screws. Maybe the factory race team noticed the fuel level difference when they pulled the domes and checked fuel level in the nozzles. Easy enough to fix with a couple of washers, so maybe they passed it along to the designers who incorporated the change for the 3-screws. ???

 

On a 4-screw w/equal length arms, I can’t recall if the nozzle was longer in the front. I believe there was a difference within the replacement ones that I bought. But I ended up setting the float distance from the inside of the float bowl lid.

 

I’m running 13/32in,(10.3mm) for the front; 16/32in (12.7mm) the rear.

 

 

Need to check how the color-tune results are, the sparks run pretty clean.

 

Edit* typo

Mine are 3 screws. I need to know if for this year both su carbs front and rear carbs are equal and if both float adjustments are the same.

Mechanic is fiddling with this needle valves and trying to adjust the float level to specs. He is trying to determine the cause of the engine tending to stall at idle. My problem has always been during long idle periods during stop and accelerate traffic jams.

maybe an over heating problem. do you have issues with long idles before it heats up? are you using ethanol free gas?

Oops, seem like this is hijacking the OP thread.

Edited February 7, 20187 yr by Dave WM

No ethanol on gas in Panama.

Back to the floats hitting the bottom of the lid or a less than optimum relationship between needle valve stem and float tang.  I simply eliminated the needle valve body sealing washer, thereby "raising" the valve assembly and helping with the float tang geometry and float position when valve closes.  I used a mark on the outside of the float bowls (both 23mm down) and clear tubing in place of bowl to nozzle hose to check level while engine running (engine ran on one carb during test).  Sparks plugs all have same color (so front and back three cylinders getting similar amounts of fuel).

 The float pivot points (ears) that hang down from the cap on 4 screw carbs were long on both carbs, Three screw carbs used long ears on the front carb and shorter ears on the rear carb. To my knowledge, the float setting is the same. Someone correct me if that's wrong. Remember that you can double check the float setting (fuel level) by verifying the fuel level is just below the  top of the nozzles with the mixture screws 2 1/2 turns down.

15 hours ago, Mark Maras said:

Remember that you can double check the float setting (fuel level) by verifying the fuel level is just below the  top of the nozzles with the mixture screws 2 1/2 turns down.

Do you remove the 3 screws then the dome, the piston and the the nozzle tube is visible then?  Turn the motor over with the coil wire off then look down in there with a flashlight and look for fuel just barely NOT spilling out of the nozzle's tube?  I've never done this but my floats are so close now I think I want to give this a try.

Best thing I've ever done was to put two rear carb lids on mine, both are short eared so no extra washers or spacers, valves are both short from ztherapy.com so that eliminated all the fuss with stacking washers.

19 hours ago, David F said:

I used a mark on the outside of the float bowls (both 23mm down) and clear tubing in place of bowl to nozzle hose to check level while engine running (engine ran on one carb during test).  Sparks plugs all have same color (so front and back three cylinders getting similar amounts of fuel).

That's the quickest and easiest "close enough" check I've ever done.  Worked good enough for me to see how far off mine were and desperately needed more adjusting.

This is a photo from zkars or jarvo2, maybe both?  Simple to do.

Here's how high mine were, if you can see the fuel in the hose way up high where the float chamber meets the lid's top.

Forgot to add I did this off the car with an electric fuel pump but it can be done a lot easier on the car.  I was rebuilding the motor at the time.

Edited February 8, 20187 yr by siteunseen

 Yup, just remove either the 3 or 4 screws, remove the suction chamber and piston. According to Bruce Palmer (ZTherapy) with the mixture screws 2 1/2 turns down. the fuel level should be 1/16" below the top of the nozzle. It's an easy way to verify the float levels are right.

On 8/2/2018 at 9:52 AM, Mark Maras said:

 Yup, just remove either the 3 or 4 screws, remove the suction chamber and piston. According to Bruce Palmer (ZTherapy) with the mixture screws 2 1/2 turns down. the fuel level should be 1/16" below the top of the nozzle. It's an easy way to verify the float levels are right.

My mechanic drilled extra holes to the ears of the front float lid in order to get a precise fuel level at the float chamber. He set the front carb to 3.5 turns and the rear to 2.5 turns clockwise. Anyway we will test the car tomorrow in traffic.