10 hours ago, Mark Maras said:

 Thanks Cap'n. I was hoping you'd respond. I had that nagging thought that it sounded too darned easy and logical. Anyone else want to chime in?

 @jalexquijano Ignore my last post to you. Leave the floats alone. (Everyone can breathe a sigh of relief) If you want to lean it out a bit (1/4 -1/2 turn) to see how it runs, try it. Most of learned by trial and error. Remember, your plugs looked nice and clean at the current settings and it runs good.

 

Mark I don't think it is too far off the mark (pun). In his suggestion: The exposed annular fuel ring will be  1mm higher so it will be slightly richer due to less energy needed to lift the fuel, but the narrower taper of the needle 1mm higher will either have no effect or slightly  contribute a mild leaning as the exposed annular ring will be narrowed.

 

2.5 turns down is simply a recommended starting point  for a factory fresh stock 240z at sea level at 20C.  There are also recommendations for changes to this height for altitude and temperature.  From experience, there are additional changes in fuel height and in needle type to accommodate engine volume changes, compression changes, cam changes, etc.

 

Just adjust until plugs look good and driving under all loads (idle, city cruise, highway cruise, acceleration) is adequate.

 

In addition to changing needles, you can put weights and stronger springs in the carb bodies to make the pistons rise less for the same engine vacuum. This can help tune towards WOT from cruise.

 

Edited July 26, 20186 yr by 240260280

8 hours ago, 240260280 said:

the narrower taper of the needle 1mm higher will either have no effect or slightly contribute a mild leaning as the exposed annular ring will be narrowed.

I think riding 1mm higher on the needle will have a significant effect. Much more effect than described above.

Easy to test... Hold everything else constant and crank your nozzle up one full turn. I think the mixture change results will be stark.

And in contrast... Not so easy to test, but if you were to drop the fuel level in the bowl by 1mm (.039 inches), I think that most people couldn't even tell the difference. Either in mechanical measurement, or in performance of the vehicle.

11 hours ago, Mark Maras said:

I had that nagging thought that it sounded too darned easy and logical.

Haha!! I agree. It sure sounds logical at first blush, but I don't believe that it actually holds.

Sure would be nice if it worked that way though!   

Lets see if i can explain myself better. Shouldnt the goal of tuning both carbs is to set the float levels to 9/16 or to be able to see the fuel 1mm below the nozzle hole when both of the fuel mixture knobs on my 1972 240z Hitachi round top carbs are set at 2.5 turns clockwise? Car seems to be running find with no misfire either at the intake or exhaust but by dialing the front carb mixture knob to 3.75 and the rear to 3.50. I dont want to get obsessed with the 2.5 starting point but thought that it would be good that both carbs could be dialed equally.

Another thing i noticed is that the car does not have enough power as a fuel injection car when stepping on 1st gear launching from a stop light. Is this also normal? How do i achive more power and response?

Edited July 26, 20186 yr by jalexquijano

What is the ratio of first gear in the transmission, and the differential?

A factory stock 1976 280Z has a 3.321 first gear ratio and a 3.54 differential ratio.  This gives an 11.76 overall ratio in first gear.

A 1981 280ZX has a 3.062 first and 3.9 rear - 11.94 overall.

Those ratios will determine how much "pickup" you'll have in first gear.  Tire size is important also but the gear ratios are more important.  You will achieve more response by increasing either of those two numbers, first gear or the differential ratio.

My 240 with the R180 will smoke my 280 with the R200. No contest at all. Now that I've put a 5speed in the 240 they're about the same on top too. 

You need to make a decision,  classic car or fast car.

10 minutes ago, siteunseen said:

My 240 with the R180 will smoke my 280 with the R200. No contest at all. Now that I've put a 5speed in the 240 they're about the same on top too. 

You need to make a decision,  classic car or fast car.

Do you have the 3.9 R180?  I've never been clear on what ratios the 240's come with.  The early 240 4 speeds were 3.592 first gear.  3.592 x 3.9 = 14.00. 

I really dont know what i have. All i know its a 1972 240z with a 5 speed 280z manual tranny. How do i verify this? Should there be a plate underneath. PO does not have this information neithe california datsun. I wouldnt likt to change the 14 inch stock wheels with 15 inch wheels and tires if by doing this will produce a negative effect at the moment of launch

You can calculate the differential gearing by jacking up so both of the wheels are off the ground. Mark the side of the tire ( I use blue tape) and the side of the drive shaft. Turn the wheel full turns while counting the turns on the drive shaft. Use those two numbers to calculate the gear ratio.


72 body with 71 interior, Eibach, Illumina, R180 CLSD, 83 close ratio, 3.90 gears, Zstory, SUs, BRE Libre wheels and front spoiler.

Lets see if i can explain myself better. Shouldnt the goal of tuning both carbs is to set the float levels to 9/16 or to be able to see the fuel 1mm below the nozzle hole when both of the fuel mixture knobs on my 1972 240z Hitachi round top carbs are set at 2.5 turns clockwise?

No the goal should be to have the engine run the best you can with what you have. The number of turns could be different for different engines.


72 body with 71 interior, Eibach, Illumina, R180 CLSD, 83 close ratio, 3.90 gears, Zstory, SUs, BRE Libre wheels and front spoiler.

I run 15" Rewinds and love them. They're not too big like the the 16"s I bought originally that now hold my 280 off the ground. They work great on the 280 but looked way out of perspective on the lowered 240. Looked like doughnuts on a Graham cracker.

Zed Head, I know zero on gearing and numbers and $^!# like that. I'm sorry. 8^(

The wide 5 from a '79ZX 2+2 works great with the R180. 80mph in 5th turns under 2,500rpm. About 2,200 on flat stretch.

Jalex I'm trying not to be a jack arse but "California Datsun" is your problem I honestly believe.  

I hope you can be happy with your 240 someday. I'll try and help but I think we've "climaxed" with your set-up.

Edited July 26, 20186 yr by siteunseen

Guess i will need to live with it.