Author Topic: Rich at idle  (Read 117 times)

Offline highlander

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Rich at idle
« on: March 19, 2020, 07:54:55 PM »
I have a carb that I rebuilt for my son's 1986 Suburban 350. It was originally equipped with an electronic carb, but the wiring has long since disappeared. I dug through my pile of Q-Jets and came up with a non-electronic carb for a 1985 Chevy 350. Anyway it idles rich enough that the mixture screws aren't doing anything. The vacuum is steady at 13.5, (we're at 5300' elevation), and if I use a small screwdriver I can feel that the power piston is fully seated. Can't detect any vacuum leaks and I did epoxy the plugs on the bottom of the bowl. I also rebushed the primary throttle shaft. I have been rebuilding these since the mid 70's and never ran into this problem before. The truck runs great otherwise. Any suggestions on where else to look for a possible fuel leak?

Offline Cliff Ruggles

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Re: Rich at idle
« Reply #1 on: March 22, 2020, 02:59:41 AM »
What is the carburetor part number?

Did you install one of my kits in it?

Offline highlander

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Re: Rich at idle
« Reply #2 on: March 23, 2020, 12:58:04 PM »
Carb #17085003 and unfortunately my kid brought me a Standard kit and new float. The only thing I thought questionable was that there wasn't any slack in the linkage for the secondaries. With the  curb idle screw backed out they appeared closed, but the linkage was tight in the forward part of the slot on the secondaries. And like I said, inserting a screwdriver above the power piston confirmed it was down all the way. Thanks for your help.

Offline Cliff Ruggles

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Re: Rich at idle
« Reply #3 on: March 23, 2020, 11:02:56 PM »
That's where the problem starts, using over the counter generic parts.  Some later carburetors for the Chevy trucks require different gaskets or they will be pig rich at idle.

Could be incorrect gaskets, could be leaking at the N/S, and for sure the accl pump "blue" seal is a complete POS.

I get carbs in here all the time with those soft blue seals ripped, torn, or have swelled up and fell off the pump........Cliff

Offline highlander

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Re: Rich at idle
« Reply #4 on: March 25, 2020, 09:41:41 AM »
The gaskets did match up with the ones that were in it. I guess if someone had previously rebuilt it using the wrong gasket that is a possibility. It does not load up and idles smooth, just rich enough that the mixture screws are ineffective. Do your kits include the specific gaskets or do they include a couple of choices? Which of your kits would you recommend?

Offline Cliff Ruggles

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Re: Rich at idle
« Reply #5 on: March 26, 2020, 03:21:28 AM »
Every kit I put together here has the specific gaskets in it based on the carburetor part number to eliminate confusion.  I recommend the SR kit.

Our kits also come with a new plastic retainer for the power piston and a complete accl pump assembly with new springs and lifetime warranty custom made seal on the pump.

The SR and HP kits will also have the secondary cam and spring, plus a new filter/spring and closed cell float.

It's not common for the later carbs to leak but the bottom plugs should be pressure tested.  If you used JB Weld over them it will leak right past it as it is not a fuel grade epoxy.  I see this with every single one that comes in here that has JB Weld on them.   The repair looks good, but they fail a high pressure air test 100 percent of the time.

There are other reasons you don't have control with the mixture screws, but it's difficult to help if you used the wrong parts/low quality parts to assemble it.......Cliff