Idle vac. drops slowly.... - Team Camaro Tech
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post #1 of 46 (permalink) Old Jan 26th, 10, 09:14 AM Thread Starter
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Idle vac. drops slowly....

Hey guys, got a holley 1850-3 w/ electric choke, stock internals, and got it running fairly well w/13 degrees initial timing/36 total (mech only dizzy) on my 327 and was running really well, and still runs really well, except if I let it idle for any length of time.

I noticed that it will start losing vacuum slowly, from 14" (I know it is low!) to 13,, 12, 11 etc then starts missfiring some.

I had already adjusted the floats to be right in spec, but wondered if this could be a sticking needle and seat issue or what.

If I give it a blast of throttle, it goes to the original higher idle vacuum and does it again. But, it wasn't doing this 2 days ago.
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post #2 of 46 (permalink) Old Jan 26th, 10, 03:59 PM
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Re: idle vac. drops slowly....

Is it a new carb? You could just have a vacuum leak. The lower your rpms the more your vacuum is effecting your engine. Have you tried using propane, or spray some carb cleaner around the gasket on the bottom of the carb. I would spray a little everywere their is a vacuum line or port. Also make sure your chock is opening all the way.

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post #3 of 46 (permalink) Old Jan 26th, 10, 05:02 PM
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Re: idle vac. drops slowly....

My guess,

First determine for sure that you dont have a vacc leak......



Otherwise Its loading up........are you sure the floats are adjusted properly?

Floats are not heavy?

Today,Holley has poor quality control..............

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post #4 of 46 (permalink) Old Jan 26th, 10, 05:42 PM Thread Starter
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Re: idle vac. drops slowly....

Quote:
Originally Posted by justincat View Post
Is it a new carb? You could just have a vacuum leak. The lower your rpms the more your vacuum is effecting your engine. Have you tried using propane, or spray some carb cleaner around the gasket on the bottom of the carb. I would spray a little everywere their is a vacuum line or port. Also make sure your chock is opening all the way.
It is a rebuilt carb. Yep, the choke is open fully. I only have the pcv line with a T in it for an in cabin vac. line (1/8th"), but took carb cleaner around the thing and didn't have any stumble etc, so I do not suspect vac. leak, at this point.

Quote:
Originally Posted by wagonman View Post
My guess,

First determine for sure that you dont have a vacc leak......

Otherwise Its loading up........are you sure the floats are adjusted properly?

Floats are not heavy?

Today,Holley has poor quality control..............
I drove it around today and drives great except for this idle issue. I went ahead and just checked the float levels and secondary was spot on and the primary was too high, so I adjusted it, and got the level down to spec. It really didn't help though. I mean, it was running good for a min or so and then it started back to before. It seems maybe a touch better, but not too noticable.

One other thing, is that I am 2-1/4 turns out at idle-seems like a lot to me. I have tried more and less and this seems to give me the highest idle vac. Has the stock 66 primaries, and 39 secondary plate. Secondaries are 1/4 turn off seat and everything appears to be in spec.

I can give it a throttle shot, and it goes back to good idle, 14" vac. then bounces a little down to around 13.5, then 13 etc and hovers there basically but seems to be missing... but it "resets" everytime I give it a tap on the throttle.

Oh, and now that I lowered the primary float, I seem to have a slight sputter off idle. Don't know if this means anything, but didn't change the accel stuff at all. At least it sputters when the engine starts running rough, but I can blip it right after blipping it to "reset" it and it does not sputter.
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post #5 of 46 (permalink) Old Jan 26th, 10, 07:30 PM
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Re: idle vac. drops slowly....

Quote:
One other thing, is that I am 2-1/4 turns out at idle-seems like a lot to me.
sec butterflys at a smiggen too far closed...which can also cause unstable idle.
Adjust the secs till the idle screw is about 1 to 1 1/4 turns and at idle speed
Then reset mixtures and idle screw..the idle screw should then be in the factory spec turns out.

My Spelling is not incorrect...it is creative

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post #6 of 46 (permalink) Old Jan 26th, 10, 08:12 PM Thread Starter
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Re: idle vac. drops slowly....

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Originally Posted by Steptoe View Post
sec butterflys at a smiggen too far closed...which can also cause unstable idle.
Adjust the secs till the idle screw is about 1 to 1 1/4 turns and at idle speed
Then reset mixtures and idle screw..the idle screw should then be in the factory spec turns out.
really? I just naturally thought that opening the secondaries more would allow more air, and thus need more fuel, but I guess I am not well versed on how the fuel would get pulled in possibly more from the idle circuit if the secondaries are opened more? Is that the reasoning? Because is sounds counter-intuitive, but I will give it a shot in the morning.

you mean adjust the secondaries till the idle speed screw is 1 to 1-1/4 turns out at idle speed? then reset the idle mixture screws?
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post #7 of 46 (permalink) Old Jan 27th, 10, 03:29 AM
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Re: idle vac. drops slowly....

I don't think it's getting enough fuel because the symptom of black smoke from the tailpipe has not been mentioned. I believe it's a misadjusted carb.

Here's what I would do:
1. Remove carb and unscrew the secondary throttle setscrew, pass side of base plate, from the plate and insert it from the top so it can be adjusted without taking off the carb. Then set it 1/4 turn in to just barely keep open the secondary plates.
2. Look underneath the primary plates and view one slot per throttle on the forward arc of the barrel. Lower the throttle curb idle screw closing the plates to make a square of the slot shown under the throttle plates.
3. Turn in each mixture screw on the metering block 1.5 turns out from lightly seated.
4. Check carb-to-manifold gasket impressions to make sure there are no leaks. Common problem if installing a square bore carb onto an spreadbore manifold - need an adapter plate.
5. Install carb, ensure carb closes from WOT. Install vacuum gauge and cap off the 1/8 inch cabin vacuum line - could be a leak within the heater-A/C system.

The reason I gave the above instructions is because I believe there is too much air bypassing the primary idle circuit - for a stock engine/stock camshaft.

Install carb, cold engine, closed choke, fast idle should be set by choke, start engine and obtain operating temperature, fast idle and all. You may need to assist by opening throttle plates alittle.

Once temp is reached, blip throttle to release fast idle cam, adjust mixture screws for best idle/highest vacuum. Stock engine should idle at 600 rpm with 15-16 inches for a 327 CID. Initial timing may need adjusting as well, no vac on cannister.

Uncap A/C supply nipple and idle should go up. Test drive without A/C supply hose connected, nipple capped.

Good luck. Let us know what happens.

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post #8 of 46 (permalink) Old Jan 27th, 10, 05:51 AM
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Re: idle vac. drops slowly....

Quote:
Originally Posted by brownnote View Post
Hey guys, got a holley 1850-3 w/ electric choke, stock internals, and got it running fairly well w/13 degrees initial timing/36 total (mech only dizzy) on my 327 and was running really well, and still runs really well, except if I let it idle for any length of time.

I noticed that it will start losing vacuum slowly, from 14" (I know it is low!) to 13,, 12, 11 etc then starts missfiring some.

I had already adjusted the floats to be right in spec, but wondered if this could be a sticking needle and seat issue or what.

If I give it a blast of throttle, it goes to the original higher idle vacuum and does it again. But, it wasn't doing this 2 days ago.
Is this car an autl trans by any chance? I ask because I had my car do the same thing before. If I had the car in gear at a light, it would idle great for about the 1st 15-20 seconds, then the idle would start to drop and it would begin to surge. If I didn't take it out of gear and allow it to idle in neutral, she would eventually stall. I had a bad cam. I had 2 wiped cam lobes. You can check this by removing the valve covers and measuring the rocker arm travel of each rocker.

Something else to check. I am guessing by the vacuum at idle(14") that you have an aftermarket cam installed? What may be happening is, with that little vacuum at idle, you may be running on the main circuit instead of the idle circuit of the carb. I am not too familiar with Holley's, but Edelbrocks and Q-Jets have a rod that controls how much fuel enters the intake given how much vacuum the rod is subjected to. If you don't have sufficient vacuum to hold the rod down in the lean stage, the rod will rise to its rich stage or power stage and tus you will be running on the main circuit and fuel will begin to discharge from the main nozzles causing a rich condition. Sometimes this also occurs from running too large a cam and having to turn the idle speed up so much that the butterflies are too far open causing fuel to be pulled from the main nozzles due to excessive incoming air speed. I believe Holley uses a power valve to control fuel delivery. The valve is stamped with a number, say 65. This means that when the vacuum drops to 6.5", the valve will open and more fuel will be introduced to the system. If your engine cant produce enough vacuum to hold the power valve closed, then it opens at idle introducing too much fuel to the system causing a rich condition. I would start by looking at the power valve and seeing what valve is installed in the carb. After that I would up the initial timing to around 18*. Then see how much vacuum the engine makes. Usually you want a power valve with half of what vacuum the engine makes. Some say to run a valve 2" below what vacuum the engine makes. If the engine makes 14" of vacuum, run a 12 power valve. Holley says, if the car is an auto, take the vacuum reading with the car thoroughly warmed up and idling in gear. If manual, just warmed up. In either case, you want to use a power valve 1/2 of what the intake vacuum reads. If the vacuum is 14", you want a valve that is half that, but, Holley says if the number you get by dividing by 1/2 lands you on an even number, you want to use the next lowest valve. If you have 14" of vacuum, half would be 7", but you want to use a 6.5 valve. Here is a link to Holleys tech info on power valves:
http://www.holley.com/data/TechServi...wer_valves.pdf

Good luck and keep us posted.

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post #9 of 46 (permalink) Old Jan 27th, 10, 06:02 AM Thread Starter
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Re: idle vac. drops slowly....

well, I haven't noticed any black smoke at least!

couple things... I do not have the fast idle cam/lever on this carb. for whatever reason it is gone (from the guy I bought it off of... fairly cheap), and then the other thing is that my 1/8th line goes to a vacuum gauge in the cabin and I have a vintage air system so no other vacuum lines other than the pcv line at all on this car. There is no brake booster, and there is no vacuum advance. It is a mechanical only unilite w/13 initial, tab bent so it hits 36 max up top.

I can take the carb off and check the primaries on the transfer slot, but I would imagine I am going to have to bump initial timing up to get the thing to hold an idle if I end up needing to back the primaries out due to the transfer slot being too exposed (will check that). The secondaries are 1/4 turn past set screw bottoming out right now, but I can triple check that.

I have 14" vacuum, most I have had before is 15" and the car idles at around 860 rpms when warmed up. It is currently starting a little hard when hot so I don't know if that helps. I have almost no room under the hood for a large spacer, in fact right now I have a heat dissipator with two metal plates and 3 carb gaskets... might try to add the last plate and gasket and see if the air cleaner doesn't hit the hood. Oh, and square bore manifold w/ my square bore carb.

I noticed that for medium vac. cars holley mentions sometimes going to bottom of secondary transfer slot on secondaries when there is more air/fuel needed to hold idle. I might try that one too, in addition to bumping initial timing up. Remember, this has the 76cc heads, so low compression, but the stumbling idle w/ bouncing vacuum wasn't an issue before that I know of.

When I hook a timing light to #1, I get random missfires... say every 10-20 secs. or so. I have new wires, and new cap and rotor, that appears to already have some carbon tracking happening too.
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post #10 of 46 (permalink) Old Jan 27th, 10, 06:30 AM
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Re: idle vac. drops slowly....

If you are getting a misfire when you hook the timing light up, you may have a cam issue.

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post #11 of 46 (permalink) Old Jan 27th, 10, 07:18 AM Thread Starter
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Re: idle vac. drops slowly....

Quote:
Originally Posted by 67CamaroRS/SS View Post
If you are getting a misfire when you hook the timing light up, you may have a cam issue.
always possible, but had it running before without the sustained idle miss, so it seems more air-fuel/spark related. That and it doesn't miss at first... it just happens as it idles.
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post #12 of 46 (permalink) Old Jan 27th, 10, 11:38 AM
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Re: idle vac. drops slowly....

If you get a rivet, hammer and shape the end into a screw driver blade, then put a 90Deg angle in the shaft , you can get to the sec idle adjustmet screw without removing the carb.

Quote:
you mean adjust the secondaries till the idle speed screw is 1 to 1-1/4 turns out at idle speed? then reset the idle mixture screws?
yes

My Spelling is not incorrect...it is creative

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post #13 of 46 (permalink) Old Jan 27th, 10, 01:01 PM Thread Starter
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Re: idle vac. drops slowly....

man, took the carb off, noticed something in the secondary idle hole (larger one, about 1/16"? so I took the baseplate off and it was a piece of metal, so that wasn't helping. I got a trick kit and replaced the needle and seats, and new gasket there, made sure everything on the plate and idle transition area was free from gunk etc. set the secondaries a hair more open, had the primary transfer slot squared on the opening, installed and waAAAAs running like a champ. Oh, 1-3/4 turn out on idle screws. then drove it all around, for 10 mins, was holding that 14" of vacuum steady, so I parked it in the driveway and started hooking up the timing light and pulled the vacuum so I could hook up my gauge and started to stumble a touch. then I got it going, revved it and it was still running rough... idled like that for a min and then died and at this point it is all I can do to get it started again!

I tried upping the primaries a touch, set them back, then went fat and lean o nthe idle mix screws and no difference. I can't get it to idle at ALL right now. nice!

Oh, was thinking it might be getting too hot, but the carb was only warm to the touch... not super hot at the base either. this has me stumped!

I will go out and try a little more secondary, because I know it wasn't to the bottom of the 2ndary idle slot yet, which holley mentions doing sometimes. I will give that a shot.
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post #14 of 46 (permalink) Old Jan 27th, 10, 02:59 PM
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Re: idle vac. drops slowly....

Do not have the sec bottomed out on the bores..this can cause jamming, bindinding and damage over long periods....dont go any more closed than a hairs breath off the bottom.

My Spelling is not incorrect...it is creative

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post #15 of 46 (permalink) Old Jan 27th, 10, 03:53 PM Thread Starter
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Re: idle vac. drops slowly....

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Originally Posted by Steptoe View Post
Do not have the sec bottomed out on the bores..this can cause jamming, bindinding and damage over long periods....dont go any more closed than a hairs breath off the bottom.
Oh, I mean I was trying to open the secondaries a little more. all I need is a #1 slotted bit and 1/4" box wrench to make adjustments.

Buuuut, I couldn't get the car started and stay started, and the battery started getting weak so I took it to autozone and they said it is bad.....that probably isn't helping things! Could that cause this miss/hard start etc?

They have a base duralast w/ 600 cca's for 80 bucks, was looking to go most cost effective/best bang for buck and wanted to know if you had any recommendations?

Also, I am running a 1100560 55a delco 1-wire alt, and they didn't have the specs to test it (or so they told me) and couldn't find the right replacement, or one better etc... have any suggestions? oh, self-exciting too.
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