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1972 Float Adjustment ...

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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

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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.

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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 by Dave WM

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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).

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 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.

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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.

IMG_1006.jpg

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.

DSC01381.JPG

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.

DSC01390.JPG

Edited by siteunseen
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 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.

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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.

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 He may have changed the pivot points but that doesn't guarantee the float level is correct. Why does he have the front carb mixture screw one full turn richer than the rear carb if the float level is correct in both. Well anyway, when he's done playing with the carbs, and hopefully it's running to your satisfaction, I still strongly suggest that you grab a screw driver, pull the chambers and pistons and verify that the float levels are correct. Remember, your goal is 2 1/2 turns down on both carbs with the fuel level (determined by the float level adjustment) just below the tops of the nozzles.

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1 hour ago, Mark Maras said:

 He may have changed the pivot points but that doesn't guarantee the float level is correct. Why does he have the front carb mixture screw one full turn richer than the rear carb if the float level is correct in both. Well anyway, when he's done playing with the carbs, and hopefully it's running to your satisfaction, I still strongly suggest that you grab a screw driver, pull the chambers and pistons and verify that the float levels are correct. Remember, your goal is 2 1/2 turns down on both carbs with the fuel level (determined by the float level adjustment) just below the tops of the nozzles.

So it should not be more than 2.5 turns clockwise each?

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.

Well my mechanic drilled a hole on the ears of the front carburetor float lid in order to get the same level on both carbs. We will test the car tomorrow in traffic to see of it still dies at idle. My problem has always been at idle.IMG-20180209-WA0027.jpg

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If the float levels are correct, 2 1/2 turns down will be close. Getting the float (fuel) levels properly set is the primary mixture adjustment. The mixture screws are the fine tune adjusters.

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Mark, I mentioned to Jalex  a few years ago what Steve says in the Just SUs DVD.  They're shipped dry, no resistance in the float chamber to slow the float against banging around during shipping.  You have his respect, I don't,  maybe he'll listen and verify the floats setting.  Good luck.

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Well i tested the car today with the front carb adjusted to 4 turns clocks and the rear carb to 2.5 turns. Mechanic considers that the fact that the depht of the hole where the needle valve seats in comparison to the depth of the hole of the other needle valve fastened in the rear carb is why he had to drill the additional hole on the lid to insert the pin and adjust the front carb to 4 turns. Anyway i was thinking that since i have another carb set i could also replace the rear lid of the other carb to see if i could then dial both carbs to 2.5 turns and then the car should have no stalling issues at idle. The only way he could have the same fuel level on both carbs is through this adjustment.

Edited by jalexquijano

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 I understand the reasoning for moving the pivot holes. I believe Cliff shimmed a needle and seat to move it down. Keep in mind that they did work with unequal lengths from the factory and they had a reason for doing it, the reason escapes me right now. I believe it was G forces. BUT, as I stated before, the mixture adjustment screws are FINE TUNE ADJUSTMENTS ONLY. The primary mixture adjustment is the float (fuel) level adjustment. Until the float level is very close to the proper setting, the fine tune adjustments (mixture screw) are not going to compensate for float levels that are too high or low. Pull the damned tops off the carbs and tell me where the fuel level is in relation to the tops of the nozzles at 2 1/2 turns down. Until we get that settled, all else is uninformed guess work.

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I crank the car again and i did notice some sputtering and hesitation while driving between 3000 to 4000 rpm. Ill check my fuel pump pressure tomorrow hoping the mechanic did not left the pump running without cranking the engine for long time.

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12 hours ago, Mark Maras said:

 BTW, I see no reason to check the fuel pressure based on the symptoms you've described.

Look the fuel pressure before i delivered the car to the mechanic was 4 to 4.3 psi. Nice pressure indeed. Just measured the pressure today and it is scarcely 3 to 3.2 psi. Could the metal filter become clogged when leaving the pump running for several minutes without the cranking the engine? If so does cleaning the metal fuel filter clear the path to 4.3 psi as when it was new? It really complicated to remove the filter with the pump fastened to the chassis.

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