1972 Float Adjustment ...

[psdenno]

2 hours ago, jalexquijano said:

i guess that with a set of pictures of both of your carbs at 2.5 turns i could undertand better what do you mean by "1/16th below the nozzle".

We seem to be flogging the deceased equine at this point.

Jalex  has asked for a picture about a half dozen times.  He's not a native English speaker and appears to be a visual learner. Since I've been a credentialed teacher for 50 years, I'd like to make a suggestion.

We need to visually define terms.  We need to use one of the carb pictures and place an arrow point at the spot that we refer to as a NOZZLE.  A top view would be best.  Next we need to show a ruler graduated in 1/16 inch increments and indicate where 1/16 of an inch would be indicated.   Finally, a carb diagram side view indicating where the 1/16 inch should be (difference between top of nozzle and top of fuel level).  Then we can have a "check for understanding" moment and press on.

Can someone use the pictures on this page to indicate that information?  I think it would be a big help in moving this process along.

Dennis

[Mark Maras]

I agree, unfortunately I don't have the computer skills to do that. 

[Captain Obvious]

The FSM documents the correct fuel level as 23mm down from the inside of the float lid. And to verify that level, you put a clear tube on the bowl outlet and check it. End of story.

But as easy as that sounds... It's not. One problem with that spec and check procedure is that since the spec is referenced to the INSIDE of the bowl lid, you cannot measure it directly (because the bowl lid is not transparent). You need to measure or estimate the gasket thickness and the bowl lid recess depth and then measure down that amount to a dimension on the OUTSIDE of the bowl. Bunch of detailed indirect measurements like that...  Not impossible, and you can do it accurately enough, but it's a little finicky.

Another problem is that if you are replacing parts, like putting in a new float or float valve, you have no guarantee that your new parts are the same as your old parts, so you won't have any idea where the level is going to end up.

So... The FSM describes a procedure for adjusting the float level based on mechanical float position only. That's where they talk about the 14 to 15 mm dimension "H" between the float and inside of the lid when the tang contacts the valve tip. But what they were not clear about is THAT IS A PRELIMINARY "BALLPARK" MEASUREMENT ONLY JUST TO GET YOU CLOSE. The final (and only important) measurement is the fuel level 23mm down from the inside of the bow lid.

SO YOU USE THE 14-15 MM "H" MEASUREMENT ONCE, JUST TO GET YOU CLOSE. AND THEN YOU FINE TUNE TO 23MM DOWN FROM THE INSIDE OF THE BOWL LID AFTER THAT USING THE CLEAR TUBE METHOD.

[Captain Obvious]

So what about this ten turns down thing? What's that all about? The ten turns down method is an alternate method of checking the fuel level instead of using a clear tube. Brian claims to have taken some measurements with a straight edge and believes he has determined (unconfirmed by me) that when the fuel level in the bowl is 23 mm down from the inside of the lid, then it should also be 1 cm down from the top of the nozzle when the nozzle is adjusted all the way up (zero turns down).

He also contends that this might be not only more convenient a measurement technique, but more accurate. That's what he was alluding to when he says this: "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."

What he's saying is that even if you have set the fuel level in the bowl to be 23 mm down from the inside of the lid, it doesn't guarantee that the level will be in the correct level at the nozzle. The REAL important level is where the fuel is inside the carb, not inside the bowl chamber. So if there is something wrong with the bowl mounting or the bolt holding the bowl to the carb is bent or something, you could have the level in the bowl "to spec", and still have the level wrong inside the carb body.

So to combat that, he's suggesting that it may actually be even better to directly measure the level inside the CARB instead because that's what's really important in the end.

And to do that, he believes the correct level INSIDE THE CARB is 1 cm down from the top of the fully raised nozzle. Doing the math using the pitch of the nozzle adjustment nut and all that yields the following:

A FUEL LEVEL IN THE CARB THAT IS TEN TURNS DOWN OF THE NOZZLE, SHOULD BE THE CORRECT FUEL LEVEL AND SHOULD ALSO CORRESPOND TO APPROXIMATELY 23 MM DOWN FROM INSIDE THE BOWL LID.

Finally, after you have used the ten turns down method the check the fuel level, you should put the nozzle level back to it's ballpark setting of 2 1/2 turns down. His not mentioning that is clearly a simple oversight. Check the level ten turns down, and then put the nozzles back where they belong when you're done.

[jonathanrussell]

With respect, I don't see how setting the float fuel level at anywhere near the top of the nozzle top at 2.5 turns would ever work. Fuel would overflow in my opinion. The 10 turn method is what I use. I don't remember where I found the 10 turn method that I use successfully but here is an excerpt that set me on the right path to getting my floats set prior to fine tuning my carbs. After you set the floats so that the fuel level is at the top of the nozzle at 10 turns, then you put the domes and pistons and needles back together, return the mixture setting to 2.5 turns down, and continue on with all of the fine tuning steps we all know and love. So, here is a copy / paste of the excerpt. I hope this helps.

 

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.

TIP: We 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 nozzle? 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.

We ended up taking 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.

[Mark Maras]

All I can gather from this is the fuel level isn't critical, which I know is BS. In group A, we have the 23 mm fuel level with the nozzles at 2 1/2 mm, leaving the fuel level FAR below the nozzle top. In group B, we have the 1/16" below the nozzle top at 2 1/2 turns. Both groups say they have had success using these settings. I have no explanation for group A's float setting. @jalexquijano, Keep raising your floats to 1/16" below the top of the nozzle at 2 1/2 turns down.

[Zed Head]

I haven't paid a ton of attention to this thread so maybe it's been referenced already.  Might not even be the right carbs.  But there are 11 pages of carb stuff in the 1973 TSB, with lots of float setting guidance, and even modifications.  Copied a couple of sample pictures, below.

Haven't really touched a carb since I rebuilt an 800 Theromoquad on a 340 in a Dodge Dart Sport.

http://www.classiczcars.com/files/category/5-service-documents/

 

[cbuczesk]

I need to prep my race car this weekend and it's time for a carb rebuild. I have clear tubes that I was using for the 23mm down measurement. At 23mm down in the bowl my car runs very well so it must be close. I'll see where 23mm down puts the fuel in the carbs. The difference between 2.5 and 10 turns is significant and I should be able to tell which setting to use when checking for correct fuel level in the carbs.

I'll take good pictures and try to figure this out.

Chuck

 

[Stanley]

Here's that tech bulletin again. Check page 3, it shows fuel level measured from bottom of the lid to be 4 mm lower for the front carb. Where it says 11.5 to 12.5 let's say 12. For 15.5 to 16.5 let's say 16. 16-12= 4. and let's figure 23 mm down at the nozzles for both carbs. The difference is due to tilt of the engine and the distance from the center of float bowls to the nozzles. Now let's forget about measuring from the underside of the lid to to of the float since its too iffy, and relate the 4mm difference to fuel level instead to check it with sightglass method. Now some easy math. All in mm, OK?   23mm average for both bowls since if Nissan is correct the 4 mm difference will put the levels for both carbs 23mm down at the nozzles. Say A = distance lid to fuel level at front carb.  B = distance lid to fuel at rear carb.

A+B = 23 x 2      A+B = 46        A-B = 4         A = B+4               B+4 +B = 46        2B = 46-4           2B  =  42     B = 42/2         B = 21       A = 46-B   A = 25

So 25 mm down front,  21 mm down rear.

TechnicalSupportBulletin-TS73-10.PDF

If you use the "fuel level in the nozzle" method you don't need this, since the levels should be the same for both carbs.

Edited March 16, 2018 by Stanley

[psdenno]

At this point, my eyes are beginning to bleed and Jalex is no closer to having a smooth running Z.  Measurements and calculations just aren't working for him.  I think Chuck's upcoming pictures may help more than anything.

Dennis

 

 

 

Edited March 16, 2018 by psdenno

[Mark Maras]

Actually Jalex reported some progress. In post #283, in his last performance description. He said that the car was running better than before, albeit at 3 1/2 turns. That tells me the float (fuel) level needs to go up another mm and recheck the nozzles at 2 1/2 turns.

[240260280]

2.5 turns is for stock cam and stock needles.   If the cam and/or needles are not stock, the number of turns may diverge from 2.5.