Triple Mikuni thread

[madkaw]

Innovation keeps me interested and challenged. I want my Z to be unique and to spread ideas to build on , because that's what these sites have done for me.

God- what did we do before the internet!!!!

[madkaw]

Put a little shine to things today

[Travel'n Man]

Steve -

Something to ponder on / thought you may want to know for an FYI - I know you are modified and this driving season I am working on jetting - once I get my arms around it I will start a new thread so all of us can post out settings and dyno results - it may help somebody later with Mikuni set up and jetting.

Per the Mikuni jet table a stock L24 should be jetted at:

40 PHH x 3 (if you have 44's the settings change per the chart)

• Large Venturi - 32
  
• Main Jet - 140
  
• Main Air Jet - 180
  
• Pilot Jet - 57.5
  
• Pump Nozzle - 0.40
  

[madkaw]

Mitchell,

that will be great for those who need a starting point. I started this thread hoping to enlighten folks on what was involved in installing and getting Mikuni's running. I really knew nothing about them before I started, so I'm learning as I go.

I'd love to see more dyno runs and postings. i realize that dynos can be different, but there is still useful information there-especially when your AFR's are layed out on a graph.

Speaking of learning-what can someone tell me about the venturi's and how they are used in the tuning process?

Edited June 20, 2012 by madkaw

[steve91tt]

As I understand it venturies are not so much used for tuning as they are used to determine the amount of air the carb can flow. Bigger venturies provide more top end power but can sacrifice drivability if they are too big for the engine.

[madkaw]

Well shortly after getting my vents fixed(opened up) on my Cold Air box I started noticing the fuel smell that would stink up my garage. I was getting dirty looks from the wife on a daily basis about the fuel. I started looking for leaks at first, and then I just took one wiff around my air filter and realized where the fuel smell was coming from.

I was trying to figure a way to remedy this and remember this other Z that had triples and he had an on/off switch rigged into his cab so he could turn the pump off with the ignition on. The owner was talking about the same issue of the fuel smell and what he did was shut the pump off a couple of blocks before he got home to empty the fuel bowls. You know what-it works. It's just a matter of judging when to shut the pump off so you at least make it into your garage:cool:

[steve91tt]

Very cool trick! I also get a strong gas smell if I park my car with the hood down. If I let it cool down with the hood up I get no gas fumes. I like the fuel pump idea.

[madkaw]

Sounds like a determination like that might only be seen on a dyno. I know the 32's are recommended for a stock L6, not sure how modified your engine needs to be to warrant a bigger venturi-sounds like a race type scenerio to me.

[madkaw]

There's probably many ways to wire this, it depends on what you want in the circuit. I wanted a ;

on/off switch accessable

enertia switch incase of the worst scenerio

fuel pump relay

fuse

I found the black/white stripe and green wire plug behind the heater panel. My car is a 9/71 and was wired for a pump, but didn't use one. This plug was used to tie in a loop circuit that would have a fused link before it went to the pump. I decided to cut off the plug end before it got to the loop and put in a on/off switch.

Lot's of advantages here-emergency cut-off, maintenance cut-off, fuel smell deterent. Just the other day I was troubleshooting my blinkers, which requires key-on, I just switched off my pump during the process.

Next I found the green power wire above the passenger side kick panel so I can wire in a fuel pump relay and inertia switch. Both items can be found at Summitt or Jegs-I chose a a generic fuel pump relay. I wanted to tie everything in right there at the kick panel. The inertia switch comes with three wires;

Normal open

normal close

ground

I tied the power wire coming from the relay to the normal/closed wire on the inertia, and then connected the ground wire on the enertia switch to the green wire going to the back of the car to the pump.

The enertia switches are only 25$, and it is a nice safety feature.

The relay got mounted next to my headlight relays tied into my fuse block.

[madkaw]

I have the car running pretty good, power feels decent and the wideband shows a nice 14+ at cruise. Still have a slight bobble that only happens at the hardest tip-in. I went ahead and rechecked my adjustment on my pilots(62.5's)and I was out over 2 turns.

So I reinstalled the 65's , and dialed them in-but I am still over 1.5 turns . My useless wideband really didnt give me a good indication of any change. Infact my gauge seemed to get more erratic with the new pilot size. I did get the engine running smoothly and-- at first, it seemed to be a bit torquier at the low end.

So I am giving these tid bits of info as background to what I did next. I decided to bolt on my vacuum log again to see if I noticed any difference. The most immediate thing I noticed when driving the car with the vacuum log installed was-- a stabilized AFR on my guage. I couldn't seem to get a stable reading when I first installed the 65's , but with the vacuum log the reading was very stable??

Also, the vacuum log also seemed to lean out my AFR. I don't believe I have any vacuum leaks, the car has a rock steady idle at 750rpm.

One last thing, is there a secret for starting the engine after it's hot? I don't have any issues on initial start up, but after driving it and shutting it down, it is difficult to get started. It usually takes a second try. I've tried different things like -one pump of the gas pedal, or giving no gas at all. Maybe I am trying to run it too lean at idle?

Current set-up

65 pilots-1.5+ turns

200-main air

160-main jets

40 acc. pumps-set on the highest setting

Vacuum log is 3/8" lines to ALL runners, and 3/8" to the PCV, and 11/32 to the MC booster

I'm going to the Midwest Heritage Z show, so I will have plenty of miles to play with the mixtures!!

[Travel'n Man]

What does your AFR gauge read at WOT (say 2nd gear at 6000RPM)?

[madkaw]

Mitchell,

I wish i could tell you, but this where my wideband fails me. It hasn't been in the budget to replace it, so I'm just doing the best I can going off my AFR's at cruise and looking at my plugs.