New 240Z build

[Travel'n Man]

The Pilot system is designed to supply the proper amount of mixture for the engine at idling and low-to-medium speeds

The Main system supplies the fuel when high output power is required as in medium-to-high speeds, acceleration, up slopes.........

Sounds like you need to discuss with Todd the proper set up for your Pilot system

[steve91tt]

I've been playing with the pilot screws. At 2.5 turns out (starting point) the car backfires and idles rough. By about 1.5 turns out everything smooths out nicely. Nothing I have been able to do with the pilot screws have had any impact on the hesitation. Do you think I may need new pilot jets?

[steve91tt]

I confirmed with Todd at Wolfe Creek that 1.5 turns out on the pilot screws is the correct setting for these carbs (not 2.5 as stated above). Todd believes that the accelerator pump system has some air in it and needs to be primed. I'll work on that tonight. He also shipped me a new part to hopefully cure my idle screw / throttle linkage issue. Great customer service!

[steve91tt]

I got the wideband working tonight. I let the car warm up and found the following AFR's:

Idle =12

cruise = 12.5

WOT = 13.5

Transition from cruise to WOT = 20ish

I think part of the high AFR at transition is due to the fact that the car misses so badly. This causes plenty of unused O2 in the exhaust which causes a very lean reading.

I moved to the upper hole on the linkage on the accelerator pump arm and transition is 80% fixed. Still a little lean (15ish) but most of the stumble is gone.

There is still some adjustment left in the pump rod so I'm going to try that next.

Looks like good numbers to me. What do you think?

Edited June 24, 2011 by steve91tt

[BZIG]

nice

[240zdave]

I would be very interested to know what kind of MPG you get with the Mikuni's. I've heard figures as low as 9 MPG, but I'm stilling lusting after a set of these.

[steve91tt]

Lots of tweaking and test driving this week.

It turns out that a miss turned set of carbs can use a lot of gas. That combined with a busted fuel gauge can lead to an embarrassing call to your wife. Car refueled...sending unit fixed.

updates...

1. I installed a helper spring which goes from the valve cover to the throttle linkage. Idle is back to a nice stable 1000RPM. I could probably go lower but I don't have the choke circuit hooked up at the moment so the higher idle helps with cold start.

2. I maxed out the accelerator pump adjustment so Wolfe Creek sent me a set of bigger accelerator pump jets. This helped the transition from low to high throttle.

3. Wolfe Creek also sent me a set of bigger pilot jets. I installed these and backed the pilot screw back to 1.25 turns out. This help the transition as well.

4. The WOT AFR's were getting up into the 14's sometimes so I moved the mains up to a size. This smoothed out the top end.

Now I have an idle AFR of 12ish. Cruise in the 12's and WOT in the mid 12's to 13ish.

The transition has gone from a severe miss to a light stutter. Much better. I'm working with Wolf Creek to see if there something else to do to get rid of the stutter.

My current setup...

44mm carbs

34mm venturis

145 fuel jets

210 air

57.5 pilots

1.8 needle/seat

45 pump jets

[madkaw]

I have my SU's running at 14.8 at cruise and around 12.2 wot. I would think that you could dial them to a leaner mixture at cruise, but wot looks good. My idle is about 13. Your stumbling sure sounded like accelerator pump issue, so it sounds like you got a handle on i!

[steve91tt]

I've spent a little more time tweeking the tuning on the carbs. I now have my idle 13-14. I took the following video of the AFR readings for the first three gears to readline.

Sorry about the quality My 9 year old copilot wasn't very steady but I think you can still see the readings. Yes, my clutch peddle is squeeky and my 2nd gear syncro is shot.:laugh:

Overall I'm impressed with how well the car runs. I'm going to try to put a few track sessions in on Thursday afternoon to shake her out at high speed.

[steve91tt]

Went to the track with the 240Z this afternoon. It ran like a top. No issues at all. According to my data logger it's about 10 MPH slower on the back straight than my other car (Rebello 3.0l with SU's) but it's actually a second or so faster around the track.

Overall a great day at the track and great little car to drive.

[Travel'n Man]

Great clip - she sounds great!

[LeonV]

Nice job Steve, you sure turned that tired Z into a solid track car quickly! Looks like you've got the Mikunis dialed in pretty well.

Did you end up using the RX7 fuel pump and a regulator? I'm still using the mechanical pump and stock fuel rail as well, but I'll be putting on a fuel pressure gauge to make sure it's in spec.