Subject: Mark's Mikuni's
From: "DOC'S" <zdoc@yosemite.net>
To: "Mark" <RenoMEG@aol.com>
Date: Tue, 5 Jan 1999

Hi Mark, Doc here, I glad to hear that you found us on the web. I can check into the ZONC Z Owners of Northern California membership in your area. or e-mail directly to the Club President Carolyn Dudley at: z300zxdud@aol.com. I believe that there are some members in the Reno
area. (Webmaster...you can contact Reno ZONC Member, Patrice Offenhauser at <Pboffy@aol.com>)

First of all since your move to the Reno area you have factored in the elevation into the equation in the carbs. From normal operation if the float levels are correct, and the carbs are synchronized correctly, then you may only need to adjust the mixtures. The rule of thumb is that for every 1000 feet of elevation you loose from 3 to 6 percent of your total horsepower. The mixture becomes richer because the air volume becomes thinner. After verifying that the initial settings are correct then go to the mixture screws. Do you have a Mikuni book? With the engine fully warmed up start with a 1/4 turn in on the mix screws. If the engine starts speeding up in Rpm's you are going in the right direction, since the engine will blubber when it is going rich, and speed up and get more efficient as it is going leaner IF it is too rich to begin with. If it is running better then go leaner on the mixture screws.
You will get to a point that it will start to miss, which indicates that it is going too lean, if that it is at all possible with you jetting as it is currently. If that is the case and you are indicating lean, then go back richer on your adjustment. This should be of some help to you from your initial settings. Have you done a Spark Plug reading? If the center electrode is black it is running too rich. This reading is used as a diagnostic tool. I am not sure of the altitude change from Sacto to Reno, but it may also be necessary to rejet the Mikuni's also. You need to perform these initial tests before I can help you past this stage.
About spark plugs, your best brands to use is either NGK or ND. These spark plugs will give you the best running in an environment that includes a colder climate too. The NGK # should be BP6ES, or BPR6ES if you are running stock ignition. Secondly you indicated that the stock fuel pump also has the factory booster pump in the rear by the fuel tank. This was an additional volume delivery booster installed on many 240Z's starting in 1973 as my recollection. There is a regular 5/16 fuel line going to the primary filter (Nissan Only brand please). Then the output of this filter goes into the electric pump. There is a 17mm nut on the bottom cover of this pump and a 1/4 turn CCW this cover will come off to reveal another filter in the bottom section of the pump. More than likely this filter may be an original one. There is also a round magnet in the center of the cover that collects any metal particles that may be in the fuel too, so check it and clean it, too. This filter is also a Nissan Dealer part, unless someone in a good parts store has experience and researched the correct part before. Thank God that you have this pump already in your "Z". It is there for more volume to the carbs and YES you need it to feed those Mikuni's!

I hope that this helps you in the situation that you are encountering with your "Z" and that I have been able to shed some light on the subject for you......

If it is necessary to talk you through more you can call me in the afternoons at my shop:

Doc's Auto Clinic
209-742-6150
Mariposa Ca. 95338
ZONC Technical Coordinator

Hi ZDoc,
I found you while searching the web for information on Z clubs. I live in Reno and as of yet to find a club close to home.

I have a '73-240Z in great shape. Unfortunately I have nagging problems setting up the carbs since moving. I lived in Sacramento when I set the car up to run a Mikuni 6-pack. It was running great until I moved up to Reno and now I am having a difficult time adjusting it to the change in altitude. Do you have any suggestions?

Second, I am using the stock fuel pump. It works well until I get into the top end of the engine and then lacks the displacement to keep up. Can you suggest an upgrade?

Last, my previous Z was a 72-240Z. Since buying this '73 model, I was surprised to find an additional electric fuel pump back by the fuel tank. I did some searching through my manuals and found this to be an addition to the later model 260Z. Why do I have it? What do I do with it? I don't remember my '72 having this. Do I need it?

Sorry for all the questions but you're the doctor.

Thanks,
Mark