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Puzzle under the hood?!


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#1 ryanonthevedder

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Posted 22 February 2012 - 07:49 PM

I have read many posts and have a lot of success with my 1973 240Z, until now. I consider myself to be a pretty good mechanic and did all of the work on my car myself (with a little help from the body guru Randy), but to the problem at hand...

The car sat for 15 years before I got to it, and I did a fairly extensive freshening up on it. I did the carbs (flat tops), re & re on the engine, high lift cam, ported head (N42). The ign is original points, but received all new parts. Then all the new metal.

The car worked great for 2.5 months then one day a problem arose. I drove the car to work in the morning, but when I went for lunch I started the car and let it idle for a minute. It started fine but then developed a little miss. I thought maybe the carbs picked something up ( I did a lot of work to get them working well/reliably) so I took it out for a burn. The problem got worse as I went and it seemed to me that the car had developed an electrical fault. It drove like someone was switching the key on and off... Once I got back to work it died and would not restart.
It has lots of spark (new coil and condenser last week)
Points OK
TDC verified on the dampener
Cam Timing Checked OK
Tank drained & new fuel (last week)
Distributor drive shaft OK
No vacuum leaks
Front carb re & re and seemed OK, both seem to be working OK
I have hot wired the coil direct from the battery to eliminate electrical/resistor problems
Compression was 145 psi after break in and is the same today

The only way the car will start and run is if I advance the timing to 30 or 40 degrees. When I get it running I cant retard it past 20 degrees or it sputters and dies.

I am at a loss... any insight would be appreciated

Cheers

Ryan

#2 beermanpete

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Posted 22 February 2012 - 09:08 PM

Rubber wires? Check for either a bare wire or a broken conductor inside the insulation on the wire that goes to the distributor from the coil. Perhaps it is only not shorting or only making a connection when the distributor is in a certain position. Replacing the wire is easy enough if it is bad.

#3 randy 77zt

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Posted 22 February 2012 - 11:42 PM

Full 12v at coil while running?

#4 rossman

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Posted 23 February 2012 - 04:52 AM

Are you sure you haven't fried your coil with the bypassed ballast resistor?

#5 ryanonthevedder

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Posted 23 February 2012 - 04:50 PM

Thanks for the tips. The coil is fine, I replaced the old one and haven't run it too much with the car hard wired. With that there was not too much change with the new coil either, although the spark was more consistent. I ran new wires from the batt. to the ballast resistor, to the coil and then on to the dist. No change, but good idea about dist. position breaking a conductor. Spark does not fail with distributor position, it just seems to quit igniting the fuel with less than 20 degrees advance. Fuel pressure was OK, 3-4 psi running, 6 with the return blocked off. There is an audible difference with each plug wire pulled while running so it is working on all 6 cyl....

any other suggestions?

I am beginning to lean towards carburation again, but when I drove it the last time it really felt electrical. If there was a fuel shut off solenoid failing I might go there, but ... I dunno. Stupid flat tops.

#6 NewZed

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Posted 23 February 2012 - 06:29 PM

I saw your thread on classiczcars. I think that Captain Obvious is right there, that you should figure out the timing issue. The engine shouldn't start at 40 degrees advance, it should just kick back and refuse to do anything.

Focus on the distributor.

Edited by NewZed, 23 February 2012 - 06:34 PM.


#7 Zark

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Posted 23 February 2012 - 06:49 PM

It is not clear if you have the ballast resistor in the circuit or not. If it is not in there then a stock 1.5 ohm coil and the points are going to get fried.

I restored a Z a few years back that had been sitting in a field for about 15 years and I thought I had the fuel tank very clean before I put it back on but I did not. After I got it back on the road I had to change the fuel filter quite often for awhile due to very fine rust plugging up the filter. Might check your filter and replace it. After 15 years there is going to be a lot gunk and rust in the tank.



#8 ryanonthevedder

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Posted 23 February 2012 - 07:10 PM

Lol, thanks Zark. Yes there was a lot of gunk in that tank. Thankfully I hot tanked it, acid washed it, and gave it the por 15 treatment. No dirt in the fuel sys.

Yeh Newzed, I am casting a pretty wide net. When I start the car you can definitely tell that it is overadvanced. It kicks a bit, but like a wounded dog it realizes I am trying to help and starts up reluctantly. If I retard it 10 degrees it won't even try to start.

Edited by ryanonthevedder, 23 February 2012 - 07:40 PM.


#9 Zark

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Posted 23 February 2012 - 08:35 PM

I still suspect the coil may be the problem. It does not take very long to damage a coil running it at 12V, a short burn as you would say could do it. I have done it. You may have an intermittent short in the winding that is temperature sensitive. Maybe the energy the the coil is put out now is so slow low that spark at the plugs is quenched as the compression in the cylinder increases and that is why it tries to run way advanced. I would pop a another coil in there and see if it is a fix. Maybe you still have the old one lying about.

#10 ryanonthevedder

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Posted 23 February 2012 - 09:19 PM

Nah, I don't think the coil is the issue. I ran the old coil up until a few days ago. I installed the new coil with the resistor in place at first and then w/ 12v. No change either way. I have a spark tester as well and the coil will fire over a 1/4 inch gap with ease.

#11 ZeeNoEvil

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Posted 25 February 2012 - 07:21 AM

[quote name='ryanonthevedder' timestamp='1330053040' post='984506']
Lol, thanks Zark. Yes there was a lot of gunk in that tank. Thankfully I hot tanked it, acid washed it, and gave it the por 15 treatment. No dirt in the fuel sys.

Pull the fuel filter and dump the contents into a clean container, check for water. This could cause the fuel cut like symptoms you described.

#12 ryanonthevedder

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Posted 25 February 2012 - 10:04 AM

Pull the fuel filter and dump the contents into a clean container, check for water. This could cause the fuel cut like symptoms you described.
[/quote]

Yep, been there already. Dumped the filter, drained the tank and did a re & re on one carb; all clean and dry. I am going to get rid of the distributor and flat tops. Time for electronic ign and SUs, 'nuff farting around.




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