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04-19-2020, 09:47 PM | #1 |
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My ‘71 won’t idle with air cleaner on.
Took my ‘71 for its first drive around the block in 20 years. Broke in the engine on the stand without air cleaner. Everything is new on the engine except the rebuilt Quadra jet. Truck runs and idles perfect without the summit brand air cleaner base (14” base open element). Soon as I lower the base on top of the carb (no air cleaner or top) the the engine rpms start to lower and soon die in any gear, slower in park & N. What’s your thoughts.
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04-19-2020, 10:22 PM | #2 |
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Re: My ‘71 won’t idle with air cleaner on.
That is interesting. Is the base touching anything other than the carburetor? Perhaps you can post pictures and that would help.
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04-19-2020, 11:26 PM | #3 |
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Re: My ‘71 won’t idle with air cleaner on.
Here’s what I got. Soon as I put the air cleaner base down the rpm go down . This pic engine cold.
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04-19-2020, 11:43 PM | #4 |
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Re: My ‘71 won’t idle with air cleaner on.
Check for interference on any of the linkage.
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04-20-2020, 12:03 AM | #5 |
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Re: My ‘71 won’t idle with air cleaner on.
Can you post a photo of the carb without the air cleaner base?
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Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377 |
04-20-2020, 09:03 AM | #6 |
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Re: My ‘71 won’t idle with air cleaner on.
The base seems to have clearance. Not touching any linkage. The electric choke conversion from Mikes carbs work find.
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04-20-2020, 12:29 AM | #7 |
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Re: My ‘71 won’t idle with air cleaner on.
I betcha your converted electric choke (from a divorced choke carb) is interfering with the lid and pushing on the choke linkage enough to close the choke blade causing your problem.
Is that a home built conversion on the choke or a kit from somewhere. |
04-20-2020, 01:18 AM | #8 |
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Re: My ‘71 won’t idle with air cleaner on.
Soon as I lay down the air cleaner base on top of the carb the rpm gos down & slowly dies. Just plain open it runs awesome no hesitation just smoke the tires and idles.
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04-20-2020, 01:25 AM | #9 |
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Re: My ‘71 won’t idle with air cleaner on.
Air cleaner base looks awfully close to the coil. Maybe try rotating it and checking the coil wire.
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04-20-2020, 03:58 AM | #10 |
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Re: My ‘71 won’t idle with air cleaner on.
ditch that low profile base, it's a truck with ample hood clearance
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04-20-2020, 09:23 AM | #11 |
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Re: My ‘71 won’t idle with air cleaner on.
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04-20-2020, 11:30 AM | #12 |
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Re: My ‘71 won’t idle with air cleaner on.
Does installing the filter and the top make a difference? I know it sounds odd but I have had problems in the past with engines at the dragstrip only running a base that disappear when the rest of the air cleaner is installed or when the base is removed. My theory is it somehow affects the venting of the carburetor.
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Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377 |
04-21-2020, 06:18 PM | #13 | |
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Re: My ‘71 won’t idle with air cleaner on.
Quote:
On some holley carbs I have seen it produce a heavy mist from pull over at high RPM. tube needs to have a cut at an angle most rochesters didn't have it do not know why. |
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04-20-2020, 09:12 PM | #14 |
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Re: My ‘71 won’t idle with air cleaner on.
I am just wondering out loud here but could that deep of a base cause the fuel vent to go into a vacume and vapor lock
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04-20-2020, 10:03 PM | #15 |
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Re: My ‘71 won’t idle with air cleaner on.
Update, when I start the engine cold, fast idle works and when warm up it fall out with the gas pedal. This is where things start to act funny engine is warm up the dual electric fans kick on and blow air across the the intake and carb and the rpms go up with fans on. If I block the air from the fans the rpms go down just enough to kill the motor in gear. Truck always fires back up. Crazy
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04-20-2020, 11:08 PM | #16 |
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Re: My ‘71 won’t idle with air cleaner on.
Yes it sounds like a problem with the air flow around the top of the carb. The base may be creating an area of low pressure above the some of the bleed orifices on the top of the carburetor. That in turn is preventing the proper mixture of fuel to the idle and possibly the main jet circuit too. Does it run okay with the filter and lid installed?
I've had engines literally die (Like the ignition was turned off) at 5000 RPM fully loaded, pulling hard just due to a bad open base plate design. 30 seconds later the same engine will start right up and run fine until another pull to 5000 RPM. Swapped a different base plate or velocity stack or no base on the carb and the problem disappeared GM engineers are a pretty sharp group. Take a look at a factory high performance air cleaner, they didn't end up being shaped like they are by accident. If it runs fine with the filter and top installed I wouldn't give it a second thought.
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Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377 |
04-20-2020, 11:41 PM | #17 |
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Re: My ‘71 won’t idle with air cleaner on.
It will not idle with the air cleaner on once it’s warm up an the fans are on. If I take the air cleaner off the air from the fans make the rpms go up just enough to prevent the engine from dieing in gear and runs great. When I block the air From the fans to the carb with anything the rpms go down.
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04-21-2020, 03:54 AM | #18 | |
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Re: My ‘71 won’t idle with air cleaner on.
Quote:
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04-21-2020, 07:34 AM | #19 |
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Re: My ‘71 won’t idle with air cleaner on.
look closely at the butterfly arm, on the inside, chances are that the base is making slight contact with that, basically to close, or the base is just slightly to small for the Quadrajet. You have an after market base, & dimensions aren't always what they should be. That base might work on an Eldebroke, but not on the Quad. I have had this very issue before, it was due to the base plate. One cheap way to check it is go to Auto Zone, & buy a spacer kit, install that, then the base on top of that ( with a gasket) see if that spaces the base plate up, there are 3 spacers in the kit, smallest one might work. As far as the running once fans come on, you are forcing air into it, its not set up to be a turbo carb, LOL. Probabaly once you fix the base plate issue, install the air filter and lid, the other will cure itself. Address 1 issue at a time,,,
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04-21-2020, 09:07 AM | #20 |
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Re: My ‘71 won’t idle with air cleaner on.
Yes, i adjusted the idle mixture screws and idle screw. If I block the air from the fans with cardboard away from the carb ( no air cleaner on)the rpm go down and kill the engine in gear and in park. I’m going to disconnect the brake booster vacuum next and plug it. No video clips allowed on this site?
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04-20-2020, 11:31 PM | #21 |
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Re: My ‘71 won’t idle with air cleaner on.
I am thinking about vacuum leaks. Do you have a thick spacer type of gasket under the carburetor, or the thin one that matches the intake properly? Is the intake smooth where it mates with the quadrajet, or is it the type of intake with the smile shaped channel cut on top (hot slot manifold)?
With the air cleaner base off, and idling well, spray carburetor cleaner around the base of the carburetor and see if the idle changes, that will detect a vacuum leak. And also, does all this funky behavior go away when you disconnect the brake booster hose and plug the hole in the intake or back of the carburetor, disconnect the distributor vacuum hose and plug the port on the carburetor it was plugged into? What is that gizmo on the driver side valve cover? It doesn't really look like a PCV valve to me, but then I am not all-knowledgeable. I would tend to disconnect all optional vacuum operated accessories, including PCV, and plug all ports on the carburetor, and see if the carburetor will tune well (you'll probably need to re-adjust the idle mixture screws) and work well and have non of that funky symptoms you describe. If you are able to achieve that, add the vacuum operated accessories back on one at at time. This is all assuming you don't find a vacuum leak due to wrong gasket or something like that. Do you have any pictures of the carburetor from various angles when it was off the engine, so we can see what all ports you have on it and perhaps can figure out which hose is supposed to go to which accessory? Last edited by dmjlambert; 04-20-2020 at 11:37 PM. Reason: correct the link |
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