Can't bring idle below 1000
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I refreshed a 1996 vortec engine and installed it in my '71. Today was the first time I took it for a good drive, when it's warmed up the idle was around 1000 and wouldn't go any lower with the adjustment screw backed out. Quadrajet 4MV
The carb had a good cleaning and rebuild kit and I put in brass bushings on the primary shaft only, the secondary seemed fine. I was reading on here for ideas and this is what I've tried so far... Blocked off the pcv line and brake booster line , no change Checked the mechanical advance action, it returns to normal on its own. I didn't check the timing.. it was set at 10 or 11 btdc the other day The other vacuum ports on the carb are plugged, I don't have the vacuum advance hooked up at the moment. I'm going to convert to manual choke , but for now I have the choke linkage held in the hot position. Anything else before I pull the carb ? Thanks This is what she looks like today. |
Re: Can't bring idle below 1000
I would start with verifying the timing, then go to the idle mixture screws. The idle speed screw is after that.
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Thanks I forgot to mention that I set the idle mixture the other day, I ended up with both around 3.5 turns for max vacuum. First time I've done it that way Yes I definitely need to recheck timing |
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Re: Can't bring idle below 1000
Also check that fast idle cam and adjustment screw is working and adjusted. That's an additional idle adjustment thingy.
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Forgot to mention that, too :) |
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I need to double check that, I believe it's kicking down all the way. I actually adjusted the fast idle up a touch today because it's just a handful of degrees above freezing |
Re: Can't bring idle below 1000
Since you had the primary throttle apart maybe you didn’t get the plates both back in perfectly. One could be hanging up on the bore.
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Re: Can't bring idle below 1000
Vacuum leak ?
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Re: Can't bring idle below 1000
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I didn't run it today, the next few days are supposed to be warmer. I took a pic of the primary, this is as closed as it goes, the transfer slots form squares ( or maybe slightly less than squares). The fast idle mechanism is fully out of the way. Should they close more than that? |
Re: Can't bring idle below 1000
Put a flashlight on the top side so you can see fitment of the plates in the bore.
Should see light evenly all the way around. Check shaft movement side to side while checking with the light. |
Re: Can't bring idle below 1000
Bottom of the carb looks great, air/fuel mixture screws look normal, and the square slots are normal.
You mentioned refreshed the engine... Is cam timing correct? Maybe off a tooth? Did you double check the distributor timing yet? Did you match the carb rebuild gaskets with the old ones during rebuild? Bob |
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Should the plates be able to close to completely cover the slots? |
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I took a picture of just about everything else.. :) I rebuilt the carb a couple of years ago, I hope I matched the gaskets.. It's running really good otherwise, cold starts, hot starts , all good so far I'll run it again tomorrow and check the timing, and make sure the mounting bolts are tight enough, I'd like to try that before I take it apart to check out the alignment of the plates |
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I’m not sure on the slot coverage. Your plates look well placed. What’s with the long screws on the secondary plates? |
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I think those screws are just what I had when I put it back together, I probably botched the stock ones.. |
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Better make sure they’re staked in place.
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Re: Can't bring idle below 1000
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I checked the timing today, its still right around 10, dwell is at 30-31.
The carb mounting bolts are snug with a 1/4 ratchet. It'll idle now at 750-800, I'm happier with that. I can definitely kill the engine by turning in the mixture screws, it seems to like 3-1/2 to 4 turns and vacuum is almost 19 inches (2300 feet elevation) This is with the idle speed screw backed out, that's as low as it goes. I've watched a couple videos saying to set the transfer slots to "squares", that's pretty much what they look like. It would be nice to get the idle down a little more. |
Re: Can't bring idle below 1000
Is your distributor vac pot hooked to manifold or ported?
Hooking it to ported would slow idle down. |
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Something for tomorrow.. thanks |
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It was disconnected, so I think that's as low as the idle will go |
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