Hi everyone, 

I recently rebuilt my front round top carb because the float valve started acting funny. I double checked my float level and it does seem to be set correctly, but when I went to tune the carbs I could not get the AF mixture correct. I'm using a color tune, and even with the mixture screw all the way up the colortune shows flame orange. 

Any ideas why the carb is always running rich?

Thanks!

 The fuel pressure should be between 3-4 psi. It'll run fine between 2 1/2 and 4 1/2 psi. Leaky float valve, stuck float, hi float level, sticking piston are the obvious possibilities. A few questions; Have you balanced the carbs? Does the float operate freely in the hanging position and does it shut the fuel supply off when it's lifted. Check it by blowing into the inlet while lifting the float. Was the old float needle the same length as the new one? How well does the engine idle, accelerate and run?  What color are the plugs?

What's the rear? Is the air flow the same? 

Just read Mark's post.

Thanks for the quick replies:

I've been following the FSM and https://zcarguide.com/tuning-adjusting-datsun-240z-su-carburetors/ for tuning. At the moment, the float moves freely and the needle valve seems to be working correctly. I have the float set to ~10mm from the cover, and I double checked that the float actually floats in water. The carbs have been balanced with the engine running at about 750 RPM.

 Describe the symptom that led you to believe the float valve was acting funny?

8 minutes ago, Mark Maras said:

 Describe the symptom that led you to believe the float valve was acting funny?

I did some exhaust work a few months ago, and when I went to put the carbs back on I accidentally attached the fuel lines to the vent on the float bowls. My dumbassery compounded when I thought it was a good idea to blow compressed air in there and clear out the extra fuel. Definitely blew the float valve. as it was basically stuck closed and would occasionally rattle open. I could start the car, but it took a while to crank over, the front bank ran lean, and I would lose power on accelerating. 

Fast forward to the post rebuild, engine starts great again and the rear carb is still running bunsen blue on the colortune. I'm using this carb as the reference, and balancing the front one to match. I'm pretty new to the carb world, so I'm not sure what variables can contribute to lots of fuel at the jet. May be I assembled the mixture screw wrong? Are the two washers supposed to be closer to the bottom of the carb, or closer to the knob?

 Is it possible you blew (literally) the float out of adjustment. I'd double check it. You can compare fuel level one bowl to the other by removing the domes and pistons, pull the choke on and look down the nozzles to see if the fuel is the same level in both nozzles.

Not sure what washers you're speaking of but here's a good drawing of the parts. Good luck.

 

I've got two washers between 28 and 29 in that diagram.

Here's what my original, nasty never touched SUs have. A thin washer almost like a smoothe flat surface for that spring to go against up top but nothing on the bottom. Sorry I can't be more help.

@zKars do have any idea? Thank you. Cliff

 

Hard to see without disassembling a few, but most of the ones I see do NOT appear to have a flat washer between the spring and the big hex nut #28, unless its much smaller and thinner than I can see. Other than increasing the spring pressure or giving the spring a kind of base, I don’t see that spacer washers are needed for anything in particular. There isn’t anything in the drawing, #29 is just a spring

Mine is so thin it looks more like a "smoother outter" for adjusting the nozzle while turning. A base as you say.

Thank you Jim!