dcraigbrown

Fair enough. My mechanical ability stops at knowing the engine needs a good air fuel mixture but short of knowing all the nuances between the needle and nozzle. I have no doubt that a lot of guys on this forum would verify the smaller nozzles would be a good option in my (high altitude) situation.

Refering to the other posts concerning the electronic ignition and losing the ballast resistor, I did both. I bought a stock zx coil and bypassed the ballast. That brought a huge improvement. I might just be dealing with a false perception now. I am curious though why just leaning out the mixture won't do the same as installing a smaller nozzle?

Ya, I think I'll try the smaller nozzles and see which needles go with. Eventually I'd like to drop an L28 in it but $$ are tight these days. Is the swap pretty much plug and play, or some modifications required? I'd be interested to hear how your'e goes.

Bruce, What size needle, price?

Yep, pretty place to live, Colorado, but really sucks the life out of internal cumbustion engines. Well, thanks for your input- you pretty much verified what I was thinking- the engine is still tight- which is a relief. After opening the plugs to .045 its doing much better. It just seems to get a little ragged too soon at high rpm- 5000 - 5500 like not quite enough fuel, a slightly weak spark or out of balance carbs, etc. I'll keep tweaking.

Yes. All read 115 - 120. Most repair/service manuals merely mention to check that all cylinders are within ~10lbs of each other. 115-120 sounds very low but it occurred to me that I'm at 6400ft and maybe an adjustment for altitude needs to be considered. I found a couple websites with conversion formulas that bring 120 up to about 150, based on 6400ft altitude. I've never seen this point brought up on this forum and it seems to me it would be a pretty important piece of information to correctly analyze compression- but maybe thats why more attention is given to the difference between cylinders rather than the numbers?? I also bought a Harbor Freight leakdown tester which showed 0% leakage on all 6 cylinders- ya, right! Well, to make a long "post" short, I've been pretty perplexed with the compression readings that seem to be good on one hand and bad on the other.

Set and forgotten. I wish I had a calibrated butt-o meter. Its been hard to tell if this car is way below its stock performance specs or not. The engine is probably a little tired but I don't have the $$ to build it like I'd want to. So working with what I have, a few things have gotten it close- I think: 1. upgrade to zx dizzy and open plug gaps 2. replace elec fuel pump filter 3. Clean and balance SU's 4. Adjust valve lash. Not sure what else I can do absent a rebuild.

Does anyone know what the plug gap should be on a 240z with a zx dizzy upgrade? I've found a few threads mentioning you can open up the gap since the spark will be stronger- but no specifics. I opened mine from .032 to the zx spec of .044. The car seems to perform better but is it best? Should I also use the plug specified for a zx or open the gap even further? Thanks for any input. I guess this isn't a HELP ME! type of question.Maybe there should be a "help me when convenient" forum:).

Anyone have any comments concerning the HEI mod? There seems to be a lot of concern about its poor performance above 3k rpm, although I have read one or two articles stating this problem is due to over-heating when the module is mounted in a distributor/coil/module integrated application- not a concern in this mod. I've also heard that the higher quality Accel doesn't have this problem. I know one answer is why bother, just use the e12-80, but they’re becoming harder to find and it would be nice to have another option. Thanks

I'm not sure what needles I have. Any way to tell visibly on the needles.

I did figure out what the problem was here. The front carb's choke was not sdjuated correctly- slightly open all the time.

I've posted a few times here and haven't really said thanks for all the help- I really appreciate it. Hopefull soon I'll get more involved but at the moment my 73 is still in pretty embarrasing shape. Well here's my question: The spark plugs in my 1,2, and 3 cylinders are black and in 4, 5, and 6 they're almost new looking. Since replacing the plugs I've only driven the car approx 50 miles so almost new looking plugs isn't surprising but given the different conditions I assume the carbs aren't tuned correctly. Would the black plugs indicate a rich condition? I've gone through the basics on the carbs. Cleaned them, set the mixture nuts to 2 1/2 turns, and balanced them by feeling the vacuum at the intake port. I'm not too concerned about getting them perfect yet due to higher priorities but hopefully someone can point me in the right direction. I live in Colorado at around 6500ft so getting the mixture right is a challenge, not much O2 up here. I'll throw this in also but if its not kosher to throw in more than one problem per post just ignore. Compression checks show about 140 -150psi in all cylinders. After putting a teaspoon of oil in the cylinders it jumps by about 30psi. This makes me suspect the rings are worn, however a leakdown test shows virtually 0% leakage on all cylinders. The tester might be out of cal but I can barely hear a hiss out of the oil dip stick port. Does this sound strange?

Thanks for the help. Using the information provided my tach is about 1% off, I guess thats not bad.

Thanks for the reply. I haven't had much luck finding the variables to plug into the formula, gear ratios, etc.

My tach in a 73 stock 240z wasn't working. After checking power and ground, and continuity from the b/w & g/w wires under the hood to the tach connector I finally determined I better pull it out and check the innards. This is where it gets interesting. The needle was pretty much hung wherever it happened to stop on the dial. I loosened one of the rear case screws and the needle became "unhung" and moved to the zero stop. When I tightened the screw it hung again. To make a long story short, the return spring is so delicate that having electrical posts or case screws too tight warped the movement enough to make it hang. Ultimately making sure the positive and negative posts were not torqued too tight fixed it- I was able to tighten the case screws sufficiently after that. Just thought I’d share that for anyone else with a non-working tach. I do have one question though, since the movement is so delicate I’m worried about the accuracy of the tach after I had my big paws inside it. As a reference in 3rd gear going 40mph the tach reads 2500. Does that sound correct given a stock 73’s gear ratio?

It has 206K on it, 100k on a rebuild.

Its a 4 speed. I believe I put straight 30wt in it. Would 20-50 be considered a higher viscosity than 30?, under normal driving conditions?

I should also mention this car is in the process of being made road worthy. I just did the 280zx dizzy mod and am still playing with the timing, getting carbs tuned, etc. This isn't a situation where the car was runnig great and then the problem suddenly appeared. Also, concerning compression. I'm in CO at about 6400ft and I found a chart that converts compression readings base on altitude, 150 is right around 180- so I guess I wasn't considering rings.

Unfortunately the tach isn't working. A rough estimate would be ~5k.

My 73 240z belches white smoke, only at high RPM. I've read enough threads here and else where to know that white exhaust can mean a blown head gasket but I don't see any water in the oil, no bubbles in the radiator when I applied pressure to each cylinder, and compression is between 140-150. I assume these tests are just backyard mechanic quickies and it still could be a blown head gasket. Are there some more likely culprits? Thanks for any help

I've read a lot of threads here about upgrading a 240z's ign to electronic with a 280zx dizzy. I decided to upgrade my 73 the same way and got an 81 dizzy on ebay for ~$20. I know that the later 280zx modules won't work so I looked up the part on the Autozone website (and Checker) and found that they list the same part number for 79-81, the picture on ebay didn't show the module clearly. Well as many of you have probably guessed, it's the wrong module. Before I start looking for the correct module I want to make sure that there's no way the 81-83 type will work. If it will work is the wiring the same? It looks like there's a second connector on the 81-83 module vs the 79-80. Any help would be appreciated. Thanks

One thing I forgot to mention, or didn't realize it was such a big variable is the altitude I'm at (6400ft). Using a chart that compensates for altitude my compression readings are around 140 psi at sea level. Better but not what I'd like to see

You're probably right- due for a rebuild :-( However I didn't warm up the car or lift the slides, it was WOT though. I'll give it a try tomorrow- the right way. Thanks for the advice.

I did a compression test on my 73 240z, stock engine, and all 6 cylinders read 112 - 117. This appears to be extremely low but I'm confused because all 6 are within a pretty tight tolerance. An oil test on one brought it up 10lbs and slightly less on the others. Does it sound like bad rings that happened to have worn symmetrically? Or am I making too much out of the close readings? Any ideas would be appreciated.

The second to last picture from left to right is the one I have.