engine is not running right after warm, movies and pictures included

[crazyoctopus]

an hour ago I took off the carbs and looked for anything that seemed out of place, and noticed that the backside of the butterflies, the back side of the piston, and the entrance of the intake manifold were damp with fuel. Note: the engine was sitting for 5 hours at this point. So I wiped it all down, pulled the floats and checked their levels still 24mm. checked all of the bolts and nuts to make sure that they were all tight, they were.

took a bit of coercing but she finally started to sputter, and while they were chugging away i pulled out the #4 spark plug, nothing happened. I pulled #2 and there was a drop, then it died.

It seems that with all of the tests that I have done, the issue is indeed with the carburetors; and more specifically the vacuum of the carbs.

solution send the carbs in to get a complete rebuild, get a new set of SU carbs, or buy some triple weber dcoe 40s.

[dustin_haru]

wow! i would trash the su's and go for triple mikunies! keep a japanese car jap, it would also give your car a better throttle response and more hp.:classic:

[akorna]

Crazy,

Your compression looks fairly even, but on the low side, but car should still run. You've mentioned in recent posts that you were setting the floats, but you described adjusting the mixture, by turning the mixture screws. Did you ever actually remove the float bowl lids and set the floats? Virtually all of the plugs show fuel fouling due to flooding or an overly rich mixture. You mentioned that you no longer have choke cables - so how are you starting/running the car without a choke? If you're just lowering the nozzles then the mixture will be way too rich. Small vacuum leaks around the throttle shafts will tend to cause a lean mixture, not a rich one. With the car dying suddenly, you have something interupting fuel flow or spark. I really don't think your carbs are bad, since there are short periods that the car will run OK from your description.

[Nigel1943]

an hour ago I took off the carbs and looked for anything that seemed out of place, and noticed that the backside of the butterflies, the back side of the piston, and the entrance of the intake manifold were damp with fuel. Note: the engine was sitting for 5 hours at this point. So I wiped it all down, pulled the floats and checked their levels still 24mm. checked all of the bolts and nuts to make sure that they were all tight, they were.

took a bit of coercing but she finally started to sputter, and while they were chugging away i pulled out the #4 spark plug, nothing happened. I pulled #2 and there was a drop, then it died.

It seems that with all of the tests that I have done, the issue is indeed with the carburetors; and more specifically the vacuum of the carbs.

solution send the carbs in to get a complete rebuild, get a new set of SU carbs, or buy some triple weber dcoe 40s.

Have you checked the needles in the carb dashpots? Are they both the same (markings on the needle shoulder) and not loose or not flush with the face of the dashpot?

[crazyoctopus]

akrona - yes whenever i removed the float bowl lids and checked float with a digicaliper. i start my car with 3-4 pumps at the pedal and turn the key; when she was running nicely she would fire right up. i guess this is a plus for living in southern california. and while i did remove the cables i did not remove the lever on the carb, so if i ever did want to check the carb i would have to reach in and pull that lever. the short periods of running okay don't really seem to happen all that often, and when they do it is in a really short burst, at least as of recently.

nigel - i haven't checked the numbers on the needles, but they are flush, secure, and straight.

[zark]

Crazy,

I noticed that you did not mention the coil when you described the ignition parts you replaced. You may have a coil that is going bad and therefore a weak spark. The fact that it starts right up (without a choke!) and then runs poorly makes me suspect the coil is going on you. With the key in start position the ballast resistor is bypassed and the coil gets 12V, in run position it gets 6V. So you can get a decent spark on start and a very weak spark on run if the coil is going bad. Temporarily rig a jumper wire across the ballast resitor to take it out of the circuit and see if it runs better. Do not leave it like this as it will enventually burn the points if the coil is good.

Also check all the push on connectors in the ignition system for tightness, at the coil, distributor, and ballast resistor.

My oldest boy has a 72 240z and a couple of weeks ago he called me from a parking lot at his college saying it would start fine but would not run well enough to drive it out of the lot. I suggested taking the ballast resistor out and sure enough it ran much better and he drove it home.

I agree with an early post, don't blame the carbs yet. The vaccum leak you describe does not sound to me big enough to be the problem. My bet is poor ignition.

[GreenZZZ]

wow! i would trash the su's and go for triple mikunies! keep a japanese car jap, it would also give your car a better throttle response and more hp.:classic:

My opinion is Mikunies are not the way to go. Trip mikunies on a stock motor do absolutely nothing when compared to a refurbished (ZTherapy) SU setup. Both deliver a mix of fuel and air proportional to the vacuum. You need the mikunies when you add more vacuum from the motor (pistons/valves/cam) than the SUs support. Mikunies are the last upgrade you do, not the first. That's the way I see it.

[Jetaway]

I'm no expert, but...

Plugs 4, 5, and 6 look Ok, or at least consistent.

Plugs 1, 2, and 3 have something and something not good going on. #3 almost looks carbon fouled (too rich) while #1 looks as if it is on the way to toasting (too lean).

Maybe its a trick of the light, but #2 in your first set of pictures and #3 in the second set look gapped.

Chris

[crazyoctopus]

zark - the coil was one of the first things i replaced about 3 months ago. And as far as looking at voltage everywhere, everything is prime and was most recently checked about 4 days ago.

jetaway - trick of the photograph, other than being discolored they are not gapped.

I will be picking up another set of plugs tomorrow and seeing if that makes a difference as far as the car running, but i did pick up a set of triple weber dcoe 40s with a mikuni, soon to be canon, intake manifold. getting these carbs isnt really a priority at this stage in the game, but it would be nice to hear my engine run one last time before the triples, 6-2-1 headers, and exhaust go on the car.

[mlc240z]

Zach,

Back in post #25 you said you pulled the wire on #4 and nothing happened, pulled #2 and it died.

If that's the case, you might only be running on 5 cylinders at that point. Pulling #4 should have also killed the engine or at least changed the idle quality.

Have you checked the #4 wire and/or plug for fault?

Quick way if you have a timing light is to clamp the light on each plug wire and look for a consistent spark while engine is sputtering.

Might not be the whole problem, but could be contributing to poor idle.

Edited March 14, 2010 by mlc240z

[crazyoctopus]

i think i am only running on 3 cylinders when i hear it running like crap. i'll try some more random stuff to see how many cylinders are actually firing when it is running horribly.

[crazyoctopus]

I'll connect the timing light to all of the wires when I try to get it running tomorrow, see if all of them are actually getting spark