steve91tt

Is that because the same part of the needle is used for idle as for 70MPH cruise?

At idle I am running 10°. It then advances to 30° (all in) at 2500rpm.

I agree, it looks like it is possible to adjust the amount the amount the nozzle moves with respect to butterfly as the choke is applied. However, I am running so rich at idle the car starts great in all weather as it is. I'm thinking that the ability to control the idle with the choke lever with minimal effect on AFR is going to be handy when I kick on the AC in the summer time.

Found something interesting and unexpected this evening. It seems that engaging my choke actually makes the car move slightly lean rather than rich. If I'm sitting and idling at 900 RPM and 12.1 AFR and engage the choke the RPM's jump to 1500 but the AFR goes up to 12.5. If I use throttle and no choke to get to 1500 RPM the AFR would be near 13 so the choke is still richening up the mixture but I thought it was an interesting observation and counter intuitive to me.

Update.... I leaned it out 0.5 turns on each carb. The idle went to 12.2 and the low speed cruise went to mid 14's. However 75MPH cruise went to 16ish. This seems a little high to me and I am getting popping from the exhaust on the down shift. So I backed it down a quarter turn. Now high speed cruise is about 15.2, idle 11.5. It seems that I can't get the idle up without going lean on the highway. Is there something I can do to the needles to help?

Would changing to a higher viscosity oil in the SU's allow me to stay richer in case 5 above and therefore allow me to lean them out with the adjustment screws for idle and cruise? I am currently using ATF in the SU's which is about 7wt oil as I understand it. This seems to be a popular oil but I have also read that folks use 20wt. If they can find it.

Sorry, I should have left more information about the car. details: 3.0 liter Rebello bottom end, stock 1973 e88 top end, Ztherapy round tops, ATF fluid in dampers, SM needles, stock air box, K&N filter, mechanical and electric fuel pump, Mallory distributor, vacuum advance is disabled, MSD ignition, no emission equipment currently installed. I am currently tuning for power.

I'm a scientist by training so I can't resist the chance to gather data and over analyze things when I get the chance. To that end, I picked up a wideband O2 meter... Wide band It's not my intention to leave the wideband installed permanently but rather just hook it up for tuning or trouble shooting. I installed the sensor in a bung in one of the down tubes in my header. The bung had always been there, just nothing but a bolt in it till now. I left the bulk of the wiring zip tied under the hood and only ran the necessary wires for the gauge which I zip tied to the steering column for easy viewing. The installation went quickly and smoothly. After calibration I started the car up and and went for a test drive. I was surprised to see that the car was running very rich. So I stopped, leaned the carbs out a click or two, drove, adjusted, drove, etc. In the end, I adjusted both carbs leaner by 1 full turn. After doing so I think I'm still a little rich in spots. Here are a few observations after leaning out the carbs by 1 turn... 1. Idle: AFR 10.5-12 depending on how hot the engine is. Generally close to 11ish. 2. 40 MPH steady speed, 3rd gear. AFR = 11-12. 3. 75 MPH steady speed, 4th gear. AFR = 14ish 4. WOT 2nd gear to redline AFR 12-13 5. moderate acceleration from 40 MPH in 3rd. AFR = 15-17 1-4 look rich to me but 5 looks very lean. Anyone have experience with these sort of tests?

Interesting, I did not know the idle could be effected by that system. I thought it was just for deceleration. I wonder if my 400-500 RPM low idle would be enough to kick in the system. If so then I will put it back on.

Correct me if I'm wrong but I thought the idle control valve keeps the butterflies open as your quickly let of the throttle and has no effect at idle. No?

I don't know if the splash shield would have an effect but I thought I'd throw it out there to see if anyone had any experience with it.

That's basically the way I tuned them a couple of months ago but I guess it wouldn't hurt to go back and make sure nothing has changed. I forgot to mention that I don't have a lower splash shield (the one that goes under the front of the engine). I know that splash shields can change the way air moves in the engine bay. Could it be that the lack of a splash shield is causing my under hood temperatures to be too high?

I wonder if I'm over-misting the fuel when hot and therefore going rich. I guess I could try leaning it out a couple of clicks and see it that changes things.

No, the idle control valve and other emission gadgets are sitting comfortably in a box under my work bench.

I have noticed lately that when my car is first warmed up the idle settles in at a nice steady 900RPM. However, if after it's warmed up I sit idling for a few minutes at a traffic light or at a drive through the idle will dip to 400-500RPM. The idle will stay low until I spend some time at higher speed (+50MPH?). When I stop from higher speed it will be back at 900RPM until I sit in one spot for a while and then I am back to low idle. The car runs great. No overheating and no stumbling at all hot or cold. It's not a big deal I'm just wondering if I'm the only one with these symptoms or if all 240Z's do the same. Car details: 3.0 liter, stock E88 top end, Ztherapy round tops, 180F thermostat, 3 core aluminum radiator, mechanical fan, shroud, insulated fuel lines, extended carb heat shield, mechanical and electric fuel pump, Mallory distributor, MSD ignition

Nice looking project car. I need to take on guage lights at some point so your photos are a great help. Keep posting!

My kids fight over rides in the Z. In fact, when potty training my twin boys the only thing that worked was to bribe them with a ride in Dad's car. If they put a dookie in the potty then they would get a ride. Two weeks later and a couple of tanks of gas, they were trained.

I put about 6000 miles on mine last year. I like a pure sports car like the 240z for around town and back and forth to work. On Long trips I prefer more of a GT car like the G37.

Sounds like a float or fuel valve issue. Does it overflow from both carbs?

Tint helps as does using a sun shade when parked in direct sun. I have a similar system in my 240Z here in Houston. Once I got the system sealed up and blowing hard (Honda blower motor upgrade) it is quite comfortable in the summer. Not as good as a modern luxury car but good enough that the Infinity stays parked I daily drive my Z year round.

Is it overflow from the float bowls?

I have the fiberglass one but the gel coat quality was excellent. Very little prep needed. Some information on the installation in the following thread... http://www.classiczcars.com/forums/showthread.php?t=38413&page=2

I had the same issue and decided to purchase the PU replica from Classic Datsun rather than trying to bang my old one back into shape. http://classicdatsun.com/ It turned out great. Hard to tell it from stock. Take a look at my "garage" for a photo. It's hard to find the part on Classic Datsun's site but give them a call and they will hook you up.

I don't think it's an aroma thing. I had a z32 with no cats. Smelled like a 240z but the only thing it got mistaken for was a Saturn. :classic:

I get "nice vette" quite often. Not sure I see the resemblance.