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73-87 Chevy _ GMC Trucks => Performance => Topic started by: 85MudMonster on January 17, 2009, 06:05:51 pm
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Okay, I got my holley carb put on today, I set the mixture screws all the way in then backed them out a full turn each one. Then set the idle to about what I thought was good. But the idle is all over the place and very choppy, I tried everything I could think of but nothing seems to get it to idle right. I went to the holley website and this is what they said to do:
QUESTION How do I adjust the mixture screws on my carburetor?
ANSWER To set idle mixture screws: 1.Get the engine up to temp 2.Shut the engine off 3.Install a vacuum gauge to a full manifold vacuum port 4.Turn the screws all the way in until lightly seated 5.Next, back them out 1 full turn and restart the engine making sure the choke is completely off 6.While at idle, back them out 1/8 turn at a time, alternating between the 2 or 4, until highest vacuum is achieved. Be sure you keep all 2 or 4 screws even. You can also do this adjustment without a vacuum gauge, the adjustment are the same except you will adjust to highest engine RPM at idle.
I did that and still nothing. I've given up for tonight, but if anyone knows the secret to the holley please let me know.
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My holley preferred 1.5 turns out. No vacuum leaks and what RPM are you setting the idle mixture at? I'd try to do it at the lowest rpm you can run the engine at. What kind of cam do you have?
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No vacuum leaks
I have learned long ago when bolting a holley to any intake I use one of those steel plates(there about a 1/32 thick) under the carb. And don't overtighten the nuts either.
You can check for leaks with a shot of WD-40 around the base of the carb while running, if the idle(or fast idle) rases when sprayed you found it.
Did you set the float level yet? Might affect your idle.
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Joe is very likely on the right track. What intake do you have? Sounds like you have a vacuum (air) leak, we just need to find out where. Lorne
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Also, do you have idle mixture screws on the secondaries?
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okay, I'm not a carb expert, but here we go....
there are only 2 mixture screws on the front of the carb, also, I know for a fact that all the vacuum lines are either hooked up or capped off. also, I have the factory cam, and the factory intake.
It is hard to set the mixture screws because the idle is all over the place. with where I have the idle screw set at right now it fluctuates between about 550-750 rpm, no matter how i adjust it it's the same amount of flutuation, then at some point in attempting to adjust the mixture screws it jumps to about 1400rpm, and at that speed it is pretty steady. then I've got to back the idle screw back down and we end up back where we started.
And finally, to answer this: Did you set the float level yet?
A: the floats have to be set???
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You have a square bore carb on a stock spreadbore intake?
here is the holley site.
http://www.holley.com/TechService/Library.asp
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yes, but I bought an adapter. I'm not that dumb.... ;)
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Also for further reference the exact hooley I have is a model 4160 Part #: 6619
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one other thing, how do I know what type of floats I have, the brass ones, the nitrophyl ones, or the plastic ones....
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No vacuum leaks
I have learned long ago when bolting a holley to any intake I use one of those steel plates(there about a 1/32 thick) under the carb. And don't overtighten the nuts either.
You can check for leaks with a shot of WD-40 around the base of the carb while running, if the idle(or fast idle) rases when sprayed you found it.
Did you set the float level yet? Might affect your idle.
couldn't find anything like that plate thing you were talking about, but I found a bit thicker one that I figured if used in conjunction with some silicon sealant would make a great reusable gasket. plus the silicone will make sure it's not leaking around the bottom.
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Dan, Do you have the 3/4" or so adapter with the Holley bolts that go up through from the bottom? Do you have a Q-jet pattern gasket on the bottom? Do you have a Holley pattern gasket on the top? Typical silicone sealer is not gas resistant & should not be used in this application. Lorne
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yes to all those questions. I've already assembled it with all the silicon and stuff. Is it going to hurt anything to have that there or what???
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yes, but I bought an adapter. I'm not that dumb.... ;)
I didn't think you were dumb.
Here a sealing plate like I use.
http://store.summitracing.com/partdetail.asp?autofilter=1&part=EDL%2D2732&N=700+115&autoview=sku
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okay here's an update, I need to know a place where I can buy a carburator that need no tuning other than adjusting the idle on it?
I know that there are no vac. leaks on this thing cause I bought those thick gaskets for the spreadbore and squarebore sides and then tightened down the area that was leaking more than the rest of the bolts and so if it is leaking then I'm just going to set the dang truck on fire cause it's pissing me off, and I just want to buy a carb put it on and set the idle and go.
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find an Edebrock carb, pit it on, and go. I fought a q jet for about a week, bought an Edelbrock at Autozone, did the pre adustments according to the book that came with it, and havent regreted a single moment of it. Well worth the money.
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was it the 1406 one that almost every parts store stocks?
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tightened down the area that was leaking more than the rest of the bolts and so if it is leaking then I'm just going to set the dang truck on fire cause it's pissing me off,
Sounds like the base plate is warped.
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Mud, I would like you to explain this in a little more detail if you would
tightened down the area that was leaking more than the rest of the bolts and so if it is leaking then I'm just going to set the dang truck on fire cause it's pissing me off,
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okay, what I did was take some carb & choke claener and spray around the base plates to try and find a vacuum leak, found a small one at the back left corner, so I went and got those really thick gaskets that they make and put those in there and as I installed the carb, I tightened it down in a criss-cross patternt but tightened that back left corner down more than the rest, that worked but only slightly. Proceeded to check for leaks again, and found none. It was still running like crap though, so I pulled the carb back off, and put the old one back on (minus all the emissions crap though). The truck actually seems to run better now, probably becuase there is no excess emissions stuff on there now. So, what I have determined is that the carb was bad, and probably need to be rebuilt.
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I think everyone here thought it was new. You could have so many problems with it that it would be impossible to diagnose it on a forum. If you buy a brand new Holley and put it on making sure you have no vacuum leaks it will run right out of the box. You will have minor adjustments as no carb can work on every possible vehicle with just one adjustment. I'd put the old one back on and wait till it is actually a problem before replacing it. Seriously if you have the stock intake on then you don't need a high performance carb. I get the feeling you want to make a few extra horsepower but aren't ready to go full tilt. If that is the case address your ignition system first and then next would be a dual exhaust. For the ignition get a good coil, module, curve kit, adjustable vacuum canister, wires, cap, rotor and plugs. Get it all adjusted to what is right for your vehicle by playing with the timing of the mechanical and vacuum advances as well as initial timing which is where you have your distributor set to. You are goin to need a timing light so you can actually keep track of what is going on too.
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I'm good on this. I dropped the holley, and bought a edelbrock 1406.