240z carb sync ignition timing disaster NEED HELP :(
Posted 25 December 2010 - 03:12 AM
Specs: 1971 240z, rebuilt straight six, one wire alternator
Tools at my disposal: Every hand tool imaginable, a timing light, a carb sync tool
First, I bought my z with four working cylinders so I, along with the mechanic that worked there, rebuilt the straight six. After we were finished, the engine ran very rough, so I drove it over to my favorite mechanic who tuned carbs with only a screwdriver in about two minuets flat. I drove the z pretty often for a couple years after that before heading off to college. After totaling my other car, I decided to drive my z to college. I drove it an hour and a half there and back several times until it broke down on me. I then towed it back home.
It took me a couple months to figure out the problem. In these couple months, me and my father had turned and returned every screw on the carbs so much that by the time I figured out that the problem was that the stupid bolt underneath the distributor had turned a half an inch, it was way too late. Now, I could only get my z to run for a very few rough seconds before it died. I then abandoned the z again after failed attempts to retune the carbs and headed back to college.
Now, onto my senior year, I decided to tow the z back to college and try to fix it in-between studies. I missed it I bought a Datsun repair manual and did my research. Through fine Datsun form sights such as this one, I was starting to make progress. I first bought a carb sync tool. I synced my carbs and played with balance screws and adjusted nuts through the directions of my manual. I also experimented with the distributor. First, I took it apart in order to better understand the part and ended up cracking the coil inside it. After a brand new distributor from auto zone I was back in business. I looked up how to get the timing from the manual and the internet. I found top dead center and set up the timing as best as i could.
I made great progress and actually got it sounding half decent for the first time in years. After attempts of fine tuning I actually ended up making it very much worse. Then, realizing adjusting the carbs wouldn't make any difference unless the car was timed correctly, I bought a timing light. This is where I am currently stuck. As I look at the timing light, I am about four or five inches away from the mark! How is this possible?! As I turn the distributor closer to the mark, the car dies. Clearly something I did was wrong. If I can't get the car close any timing marks, how can I even begin to tune this motor? I am at a complete loss and need help!
I don't know very much about motors, as I am just a body man. I learned some when I helped to rebuild the motor and from the internet and manuals but that's it. I have always been a do it yourselfer and refuse to bring it into a shop. Thank you all very much for your help. It is very much appreciated!
Posted 25 December 2010 - 08:48 AM
Posted 25 December 2010 - 09:16 AM
1. Set the timing mark to Top Dead Centre.
2. Remove the ditributor.
3. Take a photo of the distributor drive and upload here (look in additional options to do this when posting)
If the position of that drive is not 11:25 (you'll get what i mean if you read the part on setting the dizzy drive) then you'll never get your timing right and the oil pump will have to be removed to reset it.
Posted 25 December 2010 - 09:27 AM
Posted 29 December 2010 - 09:41 PM
i think the harmonic balancer either:-
-does not suit your timing cover, ie the mark that is TDC, is not aligned with 0 degrees
when it is actually @ TDC. Basically the balancer is off another car which has its timing mark furthar out of phase from the wodruff-key slot than required.
has the timing mark incorrectly marked or notched.
check actual TDC of cylinder #1, by removing sparkplu #1, get to roughly TDC, check where the timing mark sits on the degree scale on the timing cover.
to get this closer you will have to index the crank essentially, lookup indexing crank & cam procedure.
essentially screwing in a bolt into spark plug hole with an adjustable stop. rotate crank til it hits/stops, mark 0* on pulley the reverse roatation back nearly 360* untill it stops again & mark @ 0*, TDC is in between the 2 marks.
repeat with less protrusion of the stop untill the mars are about 5-8mm apart as its then easier to measure & mark.
try this first, and get back to us, before you go to other troubles of oilpump shaft etc etc, as if its running already then it might just be this.
let us know the results.
also pm me to let me know you have posted the findings here, as i may not check.
Posted 31 December 2010 - 07:42 AM
Posted 31 December 2010 - 05:57 PM
Posted 31 December 2010 - 09:47 PM
Posted 04 January 2011 - 09:31 PM
Compression test (Blown head gskt) , Spark plug leads (Faulty), Crct spark plugs (essential), Distrbtr cap (cracks/ corrosion), Coil (dfctve), Carbie's (Float units). Suitable main needles, Fuel pump & filter. Just for starters.
Also do not alter oil pump at this stage, to check if the Distribtr is out 180* simply change the distrbtr leads so that the #1 Pstn on the distrbtr cap is occupied with the #6 lead & reset your other leads accordingly. 6 2 4 1 5 3 then test it by starting.Simplest way I know of how to check this out.
Good luck. Regards:Alan.
Posted 06 January 2011 - 02:14 PM
I cant believe I forgot to mention that I had put in an electronic distributor instead of the stock. Maybe this makes a difference? I think I'm going to start over from the beginning. I was kind of teaching myself how to set the ignition timing as I went... even though I did it and redid it several times, I might have gotten something wrong. It has been a while since I did it and now I have some more things to conciser..
I have another question. In my z car manual it writes about how to begin to tune the carbs by setting them back to their original settings. However these directions are not very clear. Does anyone know of any other publications that have directions more easily followed?
P.S. Other bits of information that might be of value: I put a performance cam shaft in, and one of the biggest problems is that I had the car running pretty well, with almost zero backfiring, but I couldn't get the idle down below 1000 without it running really poorly.
Posted 06 January 2011 - 03:58 PM
I bolted a Elctrnc unit up to my existing 260 Points Dizzy set up & had similar dramas. Upon fitting the 280Z Spacer it all disappeared. "The Forum" does work.
Posted 06 January 2011 - 07:16 PM
I'm on the hunt for good carb tuning instructions! Can anyone suggest something for a first-timer??
Posted 06 January 2011 - 10:02 PM
Posted 25 February 2011 - 10:45 PM
BUT, as a qualified mechanic, I would suggest you try to find a mate of a mate who knows what he is doing to show you. L series engines are relatively easy to work with to sort out the problems you're having, but it can be a complete mystery to try to sort it out from written instructions and manuals without knowledge of what those instructions mean... You will be amazed how much quicker you will get to the bottom of it, and understand the problems if you can have someone show you how to do the things that are being suggested on the forum.
Posted 26 February 2011 - 07:47 AM
Posted 03 March 2011 - 03:08 PM
Its getting warmer and I'm back in the garage! I just wanted to say thanks again for the posts! I hit up a junk yard and found a 280z spacer and adjustment plate that I lost and now I'm trying to get it to sputter after a long cold winter! I replaced the distributor with an electronic one; replaced the spark plug wires, and the dist. cap. I'm sure I'll have some more questions soon! Wish me luck and thanks again!
Posted 20 March 2011 - 08:27 AM
In regards to tuning the SU's it's pretty strasight forward, i suggest watching some youtube vids, i found this one helpful He's using HIF carbs which are very similar the Hitachi/SU so the principles are the same.
Posted 21 March 2011 - 05:31 PM
Posted 25 March 2011 - 08:51 PM
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