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'72 Drives for 30 seconds, then stalls and hard to start


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I just bought a '72 240z and have been working to try to start it and get it running well. I have had some success and some failure and wanted to get a little help.

 

I started out with a car that wouldn't start at all. I replaced the plugs and wires as well. I drained the old fuel and replaced the fuel filter. I added 93 octane to the tank and pulled the fuel pump and manually primed the system, then reinstalled the fuel pump.

 

At this point I tried to start the car with starter fluid, and it turned over, stumbled and died. Doing this a few times, it came closer and closer to a stable idle. After about 5 times of doing this, it idled for a long time in in the driveway. I was then able to drive it around the block. It did stumble a bit, but I figured it was getting better and better so this was normal.

 

Today, however, I am experiencing different symptoms. When cold, it takes a while to get it started. It will turn on and run at 100-300 rpm for a second and die. After a little while I can get it going and it will idle fine at 600-800 rpm. When I rev it cold, it sometimes puffs fuel out of the rear carburetor inlet and stumbles. When warm this symptom goes away.

 

When warm, the car revs smoothly in the driveway, and is so encouraging I want to drive it. This is where it takes a turn for the worst. Initially I can move it well at low revs, it wont stumble and delivers power to the wheels. However, the first time the revs hit 2500-3000 rpm while delivering power to the wheels, it runs for a second and then the revs and power die down. To keep it from stalling I push the clutch in and the engine either stumbles to a really low idle or stalls.

 

After this happens, it is basically impossible to start the car until a few hours later.

 

Any ideas??? I am new to carburetors and also new to my Z.

 

On the bright side I am getting my exercise pushing the car back to my driveway, and the car isn't good enough to get me out of the neighborhood (so its not too far to push back :)).

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I would think is the Carbs that are out of tune. I wouldn't count out a timing issue at this point though.

 

Have you pulled a plug and checked it out? pull a plug(or two one from the front 3 cylinders and 1 from the back 3 cylinders) and post a picture.

 

This should let us know if it is lean or rich. Or if there are other issues present.

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The picture's of the plugs aren't working for me....

 

It sounds like a carb issue to me as well, I had similar problems with my '73 which had the floats all screwed up and some linkage installed wrong.

 

Have you checked the ignition timing?

It should be 10 degree's which can be seen on the timing tab that might need to be wiped clean as it get's dirty pretty quick making it hard to read.

 

Also, have you checked out ztherapy.com?

Best place ever if you are using the factory SU carbs.

 

If you do a quick search on how to setup the SU carbs on here you should find some good information to get the carbs setup well enough to drive it around if that is what's wrong with the car.

 

All that you will really need to buy is an airflow synchronizer to be able to match the front and rear carb's airflow.

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Right is from rear bank, left is from front bank. Thanks for the input. I will check the timing, and try to find some resources for carb setup and cleaning. Just wanted to post these pics in case you guys could tell anything else from the plugs that would help out!

 

I appreciate the response and patients!

 

IMG_2381.jpg

 

IMG_2377.jpg

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I am still getting familiar with my car and all of its pieces and parts. One I have never seen before is an air pump. I see what it does in the FSM, but wanted a layman's explanation.

 

I found out that there is no belt currently attached to the air pump, so it is not working at all right now. The second question is, do I need it and is it causing my performance problems.

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More information. After digging around and looking at the carb and air injection system on the car and in the FSM I noticed some problems.

 

1) The connection between the air gallery pipe and the 1st cylinder (forward most) is rusted and completely disconnected. Definitely an exhaust leak here.

2) The vacuum connection for the anti-backfire valve is completely broken (metal nub missing from valve)

3) I am not sure if the spring for the aft carburator should be where it is or attached the way it is.

 

It would be easier to remove the air injection system than repair it. What are the benefits and drawbacks to doing this. Also if I do end up removing the air injection system, can I live without the anti-backfire valve? If not, how do I repair it when it is not hooked up to the air injection system?

 

I did find a similar discussion a different thread, but wanted to revive the discussion a little bit.

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Following the guidance of the great members at hybridz.org, and using the FSM I have been able to start to tune my first set of carburetors. I know I still have lots to learn, and the tuning is not even close to perfect, but it is an improvement over the previous setting (see above).

 

I noticed that the nozzle on the rear carb(on the bottom of carb) was sticky and didn't move as freely as the nozzle on the front carb did. I used WD40 on both the front and rear nozzle assemblies and was able to improve their ability to move after a few minutes. I then followed the FSM method for tuning the carburetors with the exception of using the balance tool (since I don't have one). I will probably build one tomorrow since it is just a differential pressure manometer. Anyway, I balanced the flow as best I could by backing off the idle screw 1/4 turn at a time on each carb until I reached the idle required (600-700 rpm), then adjusting one screw to get a smoother idle.

 

I was then able to rev the engine and see how well it worked. I did get some good response, but the throttle hesitated if the throttle was increased rapidly. After a second of stuttering, it did rev in response to the change in throttle position. I also noticed that there was a sucking sound only coming from the rear carb when reved (or predominantly from the rear carb).

 

I got a video of the stuttering, and a backfire from the rear carb. I don't know if this is due to the still sluggish nozzle, from airflow imbalance, or from something I have yet to learn about. Suggestions welcome!!

 

Check out the video in my blog for the stutter and backfire (blog link in signature)

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First, thank you all for your help. I would probably be whining about wasting 1600 on this car if you guys weren't around.

 

Well I did have some success last night tuning the carb. I am now able to start the car with only a little effort, maybe 2 turns of the ignition. This afternoon I was able to run the car around the neighborhood without it stalling out on me (you have no idea how exciting this is to me!!!). The idle when I left was 600, but around 1800 when I returned. Not sure why, but I will re-tune.

 

Last night I also noticed that the carb that backfires reacts faster to throttle. In other words, it seems like the dashpot may need more oil to slow down the throttle opening when reved. If I use something to slow the piston down from the front, that backfire and stutter goes away.

 

I still plan on doing the following. Let me know if I am missing anything.

1) Check dashpot oil

2) Check float level

3) Build a tool to balance the carbs, and then balance the carbs

4) Check compression on all 6 cylinders (may be why I feel less air flow through front carbs)

5) Pull all the plugs again and see if they are all the same or differnt. (Then post pics for you guys!)

6) Check timing and adjust to 17 BTDC (air pump and junk removed because it was not repairable, not because I want to pollute)

7) Adjust mixture and idle again.

 

Did I miss anything? Let me know if there is one or two I should do first rather than last based on the info I have given.

 

Also, bad news. I may have heard a tick, which could be a main bearing, or it could be nothing, or it could be a slight knock due to timing.

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judging from the pictures of your sparkplugs, it looks like the fronts weren't even igniting at all. I hardly see any sign that fuel was being burnt. and they're all shiny and wet. The rears seem ok though.

 

Nicely done! The front carb was clogged, and no flow was getting to the float chamber. Now that its fixed, and I've re-adjusted the carbs, the idle is nice and smooth. I don't think Im done tuning yet, but I'm getting there. The learning curve is pretty steep here!!!

 

I also checked the dashpot oil and it was low on both carbs. So I filled that up, and it is helping the fast throttle response. I can't wait to do a test drive on all 6 cylinders!

 

I did check the ignition timing, and found it to be 15 BTDC. I know the FSM says 5 for the emissions version, and 17 for the non-emissions version. The question is, have I removed enough to be okay at 15? Currently I removed the backfire valve and the air injection. Is there anything else?

 

You guys are awesome! Thanks for the feedback (and for listening to my ramblings).

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