WARNING LONG IRL CAR POST
The tune on my Nissan / Datsun 240z is coming together!
The car has carburetors with a secondary and primary inlet.
Carburetors mix the air and fuel needed to make the engine run, in roughly precise amounts based on how much air is rushing into them. You control how much you let in with the gas pedal.
As you depress the gas-pedal the primary opens more and more and at half throttle the primary is fully open. Its giving all the air and fuel it can. As you pass half throttle the secondary starts to open.
So you have the basics there.
I swapped my 2.4 Liter motor for a larger, newer 2.8 Liter motor which has different fuel and air requirements requiring me to re-tune the carburetors. Also I have a less restrictive exhaust which causes the engine to flow easier making it even hungrier (and more powerful).
You tune a carberator by selecting the different size fuel and air jets and seeing how it feels. I also have a sensor I added to the exhaust pipe that determines how much oxygen is in the exhaust, its connected to a gauge that tells me the ratio of air/fuel the car is burning, If the number is around 14.7 Air/Fuel Im at max efficiency if its lower like at 10 air/fuel then I am ārunning richā this is a safe condition but not an ideal one, it means some fuel isnāt burning and is prolly coating everything and making a minor mess and making my exhaust smell bad. This can also sauce up the spark plugs causing them to not work at random. Running over that 14.7 A/F ratio by too much say 20 A/F Im in danger of damaging the engine.
My primaries are now tuned and I have full power to half throttle but Ive struggled with the secondaries. Ive purchased the largest jets I can find from an online store (Pegasus racing) and the car is still falling on its face at a full throttle while going up hill. A/F ratio shoots up to 22+ and the engine stumbles. So Im about to start tuning the car using huge jets Im finding on ebay from China and Czechoslovakia.
This car has been a real challenge just due to the age and rarity of some of the parts. My distributor (it distributes spark to the spark plugs) is no longer made and I had to repair it with 3D printed parts I bought off a forum.
For the longest time I was stymied by the fact that my spark timing was wrong because my vacuum advance had a hole in it. As a motor spins faster the spark has to happen earlier and earlier in the cycle so the gas has time to ignite and burn. The is achieved in part by weights in the distributor flying out and cranking the switching components forward and partly by a hose attached to the inlet track of the engine using the rising negative intake pressure to pull on a diaphragm to pull the switching components even farther forward. The device is called a vacuum advance and it uses a rubber diaphragm to operate. Over 40 years mine had worn out and developed a hole. I eventually found an old engine wizard with a magic chart that showed me what cars had vacuum advances that are cross compatible with mine. Part purchased and installed, hose re-reun and I achieved proper spark timing. Now all my tuning actually makes sense!
My spanish made carburetors were never sold for the engine Im using but are used by the British on various club racing circuits so Ive had to cobble together information about them mainly from people racing formula fords and MGs. The 240z owners kind of hate these carbs for some reason so they have no advice but the carb setups they DO favor cost a minimum of $1500 and a lot of work reworking my throttle linkage (my whole engine was $200). So I rebuilt what I have using kits and parts designed for English race cars. Weirdly the best stuff (that isnt stupid expensive) for cleaning out old carbs is undiluted pinesol. Honestly undiluted pinesol is so powerful it should have warnings all over it. It will darken aluminum and remove electroplated coatings.
Any hoo, I can drive the car now and Im very excited about it!
All my reading theory guides, parsing weird forum cultures and bullshitting with screwdrivers at 2am is resulting in a thing I can drive and enjoy which is a very powerful drug.
Now if only I had a working oil gauge or windshield wipers!
