4 Barrel Conversion - Won't Hold Idle - Nissan : Datsun ZCar forum :Nissan Z Forum: 240Z to 370Z
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post #1 of 6 (permalink) Old 09-10-2017, 04:16 AM Thread Starter
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Exclamation 4 Barrel Conversion - Won't Hold Idle

Hi all i'm the same guy that made this post earlier to try and figure out my linkage issue, but now i've got bigger problems. (I just replaced my old piece of garbage edelbrock 1406 600 cfm carb with a Holley 390 with vacuum secondaries) Every time I start the car the rpms shoot up to around 3000 and hold for a few seconds before the rpms drop and the car bogs unless I mash the pedal a few times. I've tried nearly everything at this point, I wired the choke, the vacuum advance is connected, I replaced the fuel lines going to the regulator, the regulator is pushing around 5 psi, I replaced the pcv line, I made sure I have enough gas, i'm just completely stumped. I took a video of what's going on because I know my explanation doesn't make a shred of sense. The specs of my 240 are in my signature. Thanks for any help

VIDEO: https://drive.google.com/file/d/0B0e...ew?usp=sharing

1973 Datsun 240z: L28 w/ P90 head, 600 cfm edelbrock 1406 on Arizona Z Car manifold, 6-1 headers, painted purple by PO along with a lot of other questionable modifications
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post #2 of 6 (permalink) Old 09-10-2017, 08:43 PM
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ruptured diaphragm in the accelerator pump?

73 240Z very orange
Dual Weber DGV's, header and 2.5 exhaust
Electronic dizzy with G.M. HEI module
Tokico Struts/Springs, Full Poly U bushings
Daily driver, all work done by me
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post #3 of 6 (permalink) Old 09-10-2017, 08:54 PM
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Check the choke hi idle adjustment. also verify that your vacuum advance is hooked to ported and not manifold vacuum.
If all that is well, you either have a huge vacuum leak or the carb is way off....check the float level settings, it should be right under the sight plugs at all times.
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post #4 of 6 (permalink) Old 09-11-2017, 02:49 PM Thread Starter
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Originally Posted by theghosttanker View Post
ruptured diaphragm in the accelerator pump?
I really hope not, I bought the carburetor brand new from O'Reilly's. When the accelerator pump went out on my Edelbrock carburetor it would still idle fine, but when giving minimal amounts of throttle it would bog badly. I'm not sure if the setup is different on Holley carburetors though. I had a 750 demon a while back on a 454 but I never had any problems with it so I never got the chance to tear it apart. Thank you for the suggestion!

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Originally Posted by tzagi1 View Post
Check the choke hi idle adjustment. also verify that your vacuum advance is hooked to ported and not manifold vacuum.
If all that is well, you either have a huge vacuum leak or the carb is way off....check the float level settings, it should be right under the sight plugs at all times.
I wasn't aware that there was a high idle adjustment for the choke, I'll have to look for that and i'll check the vacuum port as well, it didn't cross my mind that I might have connected the line to the wrong fitting! Regarding vacuum leaks i've heard of people spraying carb cleaner where the carb meets the manifold to check for leaks, i'm assuming that's what you mean. I'll check the sight plugs as well, i've had issues with floats in the past. I won't have a chance to work on the car until this weekend but i'll be sure to try these ASAP! Thank you so much!

1973 Datsun 240z: L28 w/ P90 head, 600 cfm edelbrock 1406 on Arizona Z Car manifold, 6-1 headers, painted purple by PO along with a lot of other questionable modifications
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post #5 of 6 (permalink) Old 09-12-2017, 12:13 AM
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The port the vac advance needs to be hooked to is on the front pass side metering plate, any other port will give you full advance all the time...not good.
PS and just for the record, I HATE holleys, the "edelbrock" has a far superior design and are much easier to tune...but heck what do I know? I still think a pair of DGVs is the best setup of all times.(not taking anything away from the SUs...)
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post #6 of 6 (permalink) Old 09-12-2017, 06:15 PM Thread Starter
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Originally Posted by tzagi1 View Post
The port the vac advance needs to be hooked to is on the front pass side metering plate, any other port will give you full advance all the time...not good.
PS and just for the record, I HATE holleys, the "edelbrock" has a far superior design and are much easier to tune...but heck what do I know? I still think a pair of DGVs is the best setup of all times.(not taking anything away from the SUs...)
Different strokes for different folks I guess haha. I'll switch the vacuum line as soon as I get a chance. Thanks for all your help

1973 Datsun 240z: L28 w/ P90 head, 600 cfm edelbrock 1406 on Arizona Z Car manifold, 6-1 headers, painted purple by PO along with a lot of other questionable modifications
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