Holley 4160 rough idle - Team Camaro Tech
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post #1 of 7 (permalink) Old Sep 18th, 09, 09:09 PM Thread Starter
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Bryan
 
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Angry Holley 4160 rough idle

I just finished upgrading my Holley 4160 vacuum secondary carb with the secondary metering plate where you can change out the jets (I took out the fixed metering plate). The car has a hard time starting like it's not getting any fuel. The weird thing is it seems to be intermittent. Early this morning it was fairly hard to start but then I got it running and adjusted the idle mixture screws and it seemed to be running great. When I went to start it again tonite it was real hard to start and wouldn't get above 2500 rpms with it floored. I'm getting 7 psi fuel pressure (on a gauge at the engine) from a Holley fuel regulator. The choke seems to be working (it's closed and opened fine early this morning). I only dropped two jet sizes (I'm at about 5200 feet).

Any ideas what this could be? Did I get some crud in the engine changing out the secondary plate? If so, how do I clean it out? Thanks.

1968 Camaro, 383 with Dart Pro 1 aluminum heads and roller cam, Holley Sniper EFI with Dual Sync distributor, Muncie M21 4-speed transmission, 3.73 12-bolt Eaton posi differential.


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post #2 of 7 (permalink) Old Sep 19th, 09, 08:49 AM Thread Starter
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Bryan
 
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Re: Holley 4160 rough idle

Okay, so I took apart the float bowls, and checked the needles and seats. I didn't see any crud in there.

I did see this plastic piece in the bottom of the primary float bowl:

What the heck is it?

I tried starting it and it wouldn't start. Also, there was a blub, blub of gas dripping out of the transition slot, a drop about every second. Is this normal?

Lastly, there was a small leak, it looked like it was underneath the diaphragm housing (somewhere around the diaphragm plunger rod).

Any ideas? Thanks.

1968 Camaro, 383 with Dart Pro 1 aluminum heads and roller cam, Holley Sniper EFI with Dual Sync distributor, Muncie M21 4-speed transmission, 3.73 12-bolt Eaton posi differential.


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post #3 of 7 (permalink) Old Sep 19th, 09, 12:00 PM
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Ron
 
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Re: Holley 4160 rough idle

That piece hangs on the 2 nibs on the primary metering block!....Install a new primary metering block gasket, a new primary float bowl gasket and a new accelerator pump diaphragm and you'll be good to go!
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post #4 of 7 (permalink) Old Sep 19th, 09, 05:10 PM Thread Starter
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Bryan
 
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Re: Holley 4160 rough idle

Cool, thanks. What does that plastic piece do?

I failed to mention that the diaphragm with the leak is the vacuum secondary diaphragm, not the accelerator pump diaphragm. Sorry. It doesn't seem like this would keep the car from starting.

1968 Camaro, 383 with Dart Pro 1 aluminum heads and roller cam, Holley Sniper EFI with Dual Sync distributor, Muncie M21 4-speed transmission, 3.73 12-bolt Eaton posi differential.


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post #5 of 7 (permalink) Old Sep 19th, 09, 05:26 PM Thread Starter
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Re: Holley 4160 rough idle

I think I might've found something. On the old metering plate, there was a thing that Holley calls a "secondary sealing plate" that's "(only required when main body has secondary power valve cavity)", part 108-122. My main body has the secondary power valve cavity and the secondary plate had that sealing plate on it, but the conversion kit instructions didn't say anything about putting the sealing plate back on. The new gasket has the big hole for the cavity, the old one didn't. I'll try putting the sealing plate back on and see what happens. I don't know why the conversion kit would have a gasket with a hole for a power valve if you're not going to use it.

1968 Camaro, 383 with Dart Pro 1 aluminum heads and roller cam, Holley Sniper EFI with Dual Sync distributor, Muncie M21 4-speed transmission, 3.73 12-bolt Eaton posi differential.


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post #6 of 7 (permalink) Old Sep 26th, 09, 08:15 AM Thread Starter
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Re: Holley 4160 rough idle

I found out that that part is called a vent baffle. It helps prevent fuel from getting up into the vent tube.

Okay, I'm totally stumped. I took the needles out and cleaned them (without taking off the float bowls) and it started up. I adjusted the float levels, and idle mixture. It ran fairly good for about a day. Then it started up rough, ran for a few minutes and then died. Fuel was leaking out underneath the vacuum secondary diaphragm area. I haven't been able to start it since.

I then took float bowls and metering blocks off, cleaned everything off with carb cleaner. I hosed off the main section (including air bleeds). I did notice a nick in the front needle gasket (so I replaced the gasket). I put the secondary sealing plate on when I was putting it back together. It still won't start, and fuel is leaking out in the same place, and fuel is blub-blubbing out still (from the transition slot on the secondaries).

I called Holley in between tear-downs and they said that fuel leaking where it's at is either too much fuel pressure, incorrect float levels, or gunk in the needles/seats. My fuel pressure is 7psi (they recommend 6-7), and my float levels are correct.

Any suggestions? Thanks.

1968 Camaro, 383 with Dart Pro 1 aluminum heads and roller cam, Holley Sniper EFI with Dual Sync distributor, Muncie M21 4-speed transmission, 3.73 12-bolt Eaton posi differential.


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post #7 of 7 (permalink) Old Sep 29th, 09, 11:05 AM Thread Starter
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Re: Holley 4160 rough idle

I finally fixed it after about a week and a half, in case this happens to any of you. It turned out to be two problems. QFT (Quick Fuel Technology, they are the guys that make the metering block conversion I put on) clued me in on the carburetor leaking problem. They thought that the main body was warped. I think it was actually leaking out of the throttle shaft (which attaches to the vacuum secondary diaphragm rod is). The carb is not that old (only about two years) so I hadn't thought about it being warped. I filed down the face of the main body until the float bowl didn't make any noise rocking when I tapped on the corners without the gasket on. That got rid of the fuel leak (after the floats were adjusted again).

The carb leaking/running rich caused my plugs to get fouled. I replaced the plugs and it starts good and is running pretty good so far today. Hopefully the leak doesn't come back, but so far so good. I did half to dial back my timing a bit because it was detonating when I floored it, I think due to going one size hotter on my plugs. Oh, and I also had to replace a needle valve o-ring that got torn when I was pulling the needles in and out.

1968 Camaro, 383 with Dart Pro 1 aluminum heads and roller cam, Holley Sniper EFI with Dual Sync distributor, Muncie M21 4-speed transmission, 3.73 12-bolt Eaton posi differential.


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