New 1971 240z, Help please! (carbs)

[aanzures07]

Hi everyone,I'm a 19 year old college student and i just got a 1971 Datsun 240z with 115k miles on the original l24 motor and 4 speed transmission. The car caught my attention right away. It has had quite a bit of work done and looks pretty nice. It used to be blue but the first owner painted it yellow. He did alright except for the loser didn't sand the blue all the way down and you can see it through a couple chips in the paint. It has pretty sweet body kit and some centerline wheels wrapped in low-profile tires. The interior is pretty nice. It is complete and has no tears or rips. The door panels are custom made but the racing buckets in there are so big they rub up against them. Overall it is a nice car and has no rust at all. It already looks nice so i'm not too worried about the exterior, but i would like some advice on the engine.

At the moment the SU carbs are set to run rich and the car has horrible fuel economy (about 18MPG!!) . Since i am a college student i would like to tune them down to get better fuel economy, but i have no idea on how to do it. Can someone help me? Thanks!

Here are a couple pics:

The car..

The engine..

The interior:

oh yeah the car also came with an extra L28 engine, 5 speed transmission, and rear axle out of a 1979 280z. I'm not sure about the when it will happen but i plan on rebuilding it and droppig it in.

[hitbychance]

very nice z man congrats

[AZhitman]

Beautiful.

Welcome aboard!

As far as tuning the SU's, there's several methods, but you'll need an air flow meter... otherwise you'll be tuning by ear.

This book is a great read and a must-have for anyone looking to do their own SU's: http://www.amazon.com/Build-Po...0698X

My favorite article: http://www.team.net/www/morgan/tech/tuning.html

[evildky]

congrats on the car, looks nice, the seat issue is common, most aftermarket seats are just too wide for these old cars, and 18 mps on SU's isn't bad, you can try leaning them out (just turn the jets in a half turn each or untill it starts to stumble) but if you want fuel econeom you got the wrong car, I've heard some high mpg claims but mostly from people not intelligent enough to actually calculate their own milage

[NSR_s30]

Yeah I don't know if you'll get fantastic MPG's out of the L24. As for tuning the carbs, it's really easy. The only down fall is you need a flowmeter. I own one and it definitely makes it easier to tune them.

[aanzures07]

Thank you all for all your help. I have looked at the article and the book and am now looking at purchasing a flowmeter. Thanks.

[240Zilla]

I had a 1971 for many years and think it's the best possible year of Z! Happy that you have the SU carbs and want to stick with them. When properly tuned they are more efficient than fuel injection. Just that you have to stay up on keeping them adjusted. The easiest thing to get out of whack is the fuel level in the float bowls.

#1 important thing is that both carbs have to be EXACTLY equal in all the possible adjustments. Least important (but still important) is the base idle be the same for them both. The flow meter will help you with this but more important is the balance above idle. The most important setting is the mixture and this also must be matched between the two.

Start by setting float bowl level and there are several ways to gauge this. My preferred method was to idle the car just fast enough so it would vibrate as little as possible. Shut it off abruptly, then unscrew the four screws that hold each carb's oil dampner in place. With the air filter removed, put a finger in the carb and lift the dampner as you also lift the housing up. Be very careful not to bend the needle (this is critical!). Lift the housing and dampner as a unit and set them down somewhere safe. I usually would set them on the grill in front of the windshield so the needle is safely extending down in one of the slats. Then focus your attention in the jet where the needle was formerly residing. Use a flashlight if necessary to check the fuel level. See the shiny surface of the fuel level and estimate how far down it is from the top. It should be below the top but not too far down. Experiment with different levels as this is your fundamental gauge of how rich/lean the SU will run. The MOST important thing is that both carbs must have the same exact level when you look down the jets. All other adjustments will base on this setting. If there is any difference, or you wish to raise or lower the level then you must pull the float out of the bowl and tweak the metal tab ever so slightly. This process is so frustrating because most tiny tweaks make no difference yet you nudge it just a little more and there is a huge difference in the level. You must be patient and be prepared for hours of trial and error before you get it right. Then repeat with the other carb until both are EXACTLY the same.

I eventually converted to electric fuel pump (at the tank) and this made it much easier, plus solved the hot weather vapor-lock problem. There is actually a pair of wires built into the harness for this purpose but never used in the production car. To power up the wires you should install a fuse at the other end of the harness which is somewhere near the front of the transmission tunnel, inside the car near the radio. Look for an unused white plastic connector that is taped up inside the car and a pair of wires with "bullet" connectors taped up near where you'd naturally want to put the pump at the tank.

With the electric fuel pump in place you can power the ignition without bumping the starter and this will fill the bowls to their level so you can check. If the jets are very close to the top or even overflowing when the pump is on then the float is definitely set too high. This could be the source of major fuel waste. Better to try a little low (but equal) and go from there. The mixture adjustment can bring it back rich but never can lean it enough to compensate for a float set too high.

My experience driving my 240Z was between 17-22mpg for the most part. One time I did get 27mpg but I was driving 110mph for almost the whole tank! Those cars are meant to be driven fast! Also it was in the southern Nevada desert and the temp was about 105F.

Also make sure the oil in your SU carb's dampners is SAE 20W. If you have any trouble finding this, go to a motorcycle shop. They use it for the dampners on the front forks of some off-road bikes. It must be single-weight 20, accept no substitute!

[minnesotazcar]

Welcome to the club really beautifull z man very nice. Im going to give you the secret to getting mpg out of your classic z car.... Put the 5 speed in... There is some good advice for tuning the cars my personal advise is always if they arnt broke dont f**k with them. If you have no hesitations stutters flames blowing out the tail pipe then drive it. Those carbs are tricky and if you dont have to mess with them i wouldnt.

[240Zilla]

I had a 1971 and when the original 4-speed decided to die I had to replace it with a 5-speed. As far as I know there was no 5-speed offered for the early Z's so I found one from a 1980 ZX. It bolted right in but there were some challenges.

The first two years of the 240Z had a different kind of shift mechanism and the shift boot is located 3-4 inches farther back then in later years. This meant I had to put a zig-zag bend in the base of the lever and notch the sheet metal. Also there was no way to use a proper boot so I had to use one of those universal types and drill screw holes.

Another problem is the clutch throwout geometry is slightly different and requires a mix and match combination of old and new style parts.

[evildky]

someone is repeating themselves and yes there was a factory 5 speed avaialbe in the s30's, the 77-78 model had it as an option, they basically added a 5th geatr to the 4 speed and they weren't very strong, and the clutch geometry that changes betweent he transmissions is all in the TO collar, just use the one intended for the trans you are using, there were 3 sizes and you can get away with the mid size collar in any of the trannies, it's the only one still available form nissan