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Thread: weird running issues suspect vacum advance.

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    Registered User 2sixTZombii's Avatar
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    Default weird running issues suspect vacum advance.

    I'll start off by explaining that my clutch is still mostly fubar, but after bleeding it again, and readjusting the pedal she is perfectly drivable again, so long as I take it kinda easy.
    My Z has always(since I got it running) idled what I've gathered to be kinda high about 1050 or so, it doesn't drop much more than even that with idle screws backed out all the way. But it gets so crappy below 1000 that I keep it right there. At idle its alway had an ocassional miss or pop, when running parked it will alway leave black flecks on the ground directly behind the tailpipe and when I let off the gas it smells like gas and kinda ****ty. All that aside it gets decent MPG and seems to have plenty of power, so for I wasn't too concerned. In some ways it sounds like its running rich, but it felt like it ran lean, seems to have a little power with the choke a 1/4 closed, an obvious sign if being jetted to small. When I first swapped these carbs on I replaced a needle and seat but until tonight hadn't pulled off the air cleaners since I started driving it. I've been having a weird random every couple months fuel system issue where the car starts starving for fuel unltil I disconnect and reconnect the in on the pump. Then I'm fine for two more months. Well it did it three times in one day the other day, then undoing the fuel line wouldn't help and it seemed as though the fuel was barely moving through the clear filter. I was on a back road in a rain storm in Nebraska when this happened, so I pulled out my emergency puralator pump and ghetto hooked it up under the hood, and it ran fine then at first then started running ****ty, but I was fine to drive home. Iwas pretty sure my fuel pump(the same one that was in while it sat 14 years) was my issue, so the purolator ghetto as my back road install was should have cured all my issues, but it ran really crapping and missed like hell the whole way home. Well I tried alot of things, and then just bought a vacum/fuel pressure gauge. And found that with my puralator I had 5 PSI to my carbs, which is great, and with the old pump I had a shaky 1.9 PSI. So it finally hit to pop of the air cleaners now knowing that they were getting fuel. And sure enough, the secondary on the back carb was full of gas leaking past the needle. So I changed out the needle and seat with a good back up and fired her up, she was running great butter smooth idle but now I'm idling at 750, but it sounds perfect, no missing no popping. No black flecks on the driveway or gassy smell, pulled strong, cruised smooth, ran better than ever. Decided for kicks to see what my vacum pressure was pulled the vacum advance off the dizzy and hooked it up to the gauge, nothing, pulled the line of the gauge car didn't even stutter, felt it and out of this line( the one at the base of the carb had vacum, I don't think the fitting was ever drilled out. So I hooked the line up to a good vacum source and for what is likely the first time since the 90s hooked the vacum advance to a vacum source. Ran a little different, figured well we set the timing(by ear) with no working advance, makung it needs tweaked, so I tweaked it by ear, and back to a perfect idle took it for a spin and under load its pulling hard, and feels great, but I start cruising at one speed and it starts running ****ty and feeling really stumbly unless I get on it, then its great. Pull in the driveway were idling weird as hell at 950-1100, and now theres popping and missing. Thsi is with or without the vacum advance connected now, no difference. My only theory is that because how long it sat when the dizzy advaced the vacum advance weight didn't return, making it really run weird I until get on the gas and which I believe is when its suppossed to advance anyway. Not sure how to fix this or even tell if this is indeed it, but I'm pretty confused, and I hope I can get it to run that smooth again.
    1974 early 260z, Weber DGVs killed my motor.....

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    Registered User 2sixTZombii's Avatar
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    Wow, by the time anybody gets done reading that book, I'll have figured this out on my own. Oh well
    1974 early 260z, Weber DGVs killed my motor.....

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    Shine some light on the damper pulley and its timing marks.
    1976 280Z, with some minor modifications

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    Registered User 2sixTZombii's Avatar
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    Figured out that the vacum advance is indeed supposed to have no vacum at idle, so that was a mistake, reconnected it where it goes, even tried disconnecting it all together, made no difference. I put my timing light, the notch on the pulley was at the 20 degree mark, at 700 rpm. I took it out to an empty parking lot, and advancing the timing a little at time, doing a lap in the parkng lot after each adjustment, then dud the same retarding it. And while the car ran different during each setting, the base problem stayed the same. It runs good if I'm accelerating at all, but if I hold it at one speed, it runs like crap, in any gear or speed. I tried adjusting the idle screws, also to no avail. I suspect the weber DGVs are the issye again. I hate these carbs.
    1974 early 260z, Weber DGVs killed my motor.....

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    Registered User beermanpete's Avatar
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    It sounds like you could have a lot of dirt in the fuel system. Have you cleaned the fuel tank? The poor cruise that improves on accel sounds like to much fuel (rich). Check the float height or fuel level in both carbs. Make sure there is no fuel dripping from any of the discharge parts at idle.

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    Registered User 2sixTZombii's Avatar
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    Quote Originally Posted by beermanpete View Post
    It sounds like you could have a lot of dirt in the fuel system. Have you cleaned the fuel tank? The poor cruise that improves on accel sounds like to much fuel (rich). Check the float height or fuel level in both carbs. Make sure there is no fuel dripping from any of the discharge parts at idle.
    After some work it looked like the back carb was running rich,I tried a few things than took it for a test drive, coming up my street on my way back home, right before a shift at about 4k the linkage on one carb came apart, not sure how this caused it but while limping it back home not sure yet why it running so goofy(I was a block away) a rod started knocking. I had a friend who used to be a machinist come over and give it a listen and he said rod knocking or possibly broken piston skirt..... So with winter fast aproaching I am now looking at motor swap, or rebuild. For the record, I tried resetting float levels, different jets, different floats entirely, I've both these carbs off and open abput tens in the last week, I'm sure with a little time I could figure these DGVs but I'm done with them, if I gave up sooner and bought some SUs I wouldn't be here, and I hate these DGVs they belong on my brthers subaru, not a Z
    1974 early 260z, Weber DGVs killed my motor.....

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