Author Topic: Quadrajet has more power when choke is on  (Read 172 times)

Offline Brboles

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Quadrajet has more power when choke is on
« on: January 03, 2019, 09:18:20 AM »
I have a 1986 c20 350 factory carb 17085003. The truck has good power going down the road but seems to have better power when the choke is on. The timing is set good. Just can

Offline Brboles

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Re: Quadrajet has more power when choke is on
« Reply #1 on: January 04, 2019, 10:20:21 AM »
My timing is set for 12 degrees btdc at idle. Is that too low and causing my issue?

Offline 429bbf

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Re: Quadrajet has more power when choke is on
« Reply #2 on: January 04, 2019, 08:09:45 PM »
i would say no . seems like its running to lean . I'm surprised that's the stock carb if my memory is correct most of them were on 454s in 1 ton chassis what type of gas are you running and did it just start doing this . they add more ethanal to the gas is some areas of the country this time of year . can you get some straight 91 and see how it runs ? hth.

Offline Brboles

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Re: Quadrajet has more power when choke is on
« Reply #3 on: January 04, 2019, 08:25:56 PM »
I sure can. I will try it for sure. I just assumed that it was the original carb. I
« Last Edit: January 04, 2019, 08:44:10 PM by Brboles »

Offline Brboles

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Re: Quadrajet has more power when choke is on
« Reply #4 on: January 04, 2019, 08:51:29 PM »
I will certainly try. I just thought this was the original carb and it could have certainly been changed through the years. I have tried to riches truck idle mixture but no change really. I have a new distributor cap and rotor with AC Delco plugs rapid fire .045 gap. I have noticed that there is a sharp bend in the fuel line going into the carb. Could that be part of my problem?

Offline Brboles

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Re: Quadrajet has more power when choke is on
« Reply #5 on: January 05, 2019, 07:46:16 PM »
What else can I try other than higher octane to richen it?

Offline Cliff Ruggles

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Re: Quadrajet has more power when choke is on
« Reply #6 on: January 06, 2019, 01:56:55 AM »
The sharp bend wouldn't matter unless the line is kinked, crushed.  Hopefully the fuel line is solid metal and not rubber hose in it.

If you don't have control with the mixture screws and running lean time to pull the carb down for a good cleaning and replace the internals.  This will get it working correctly and up to par for this new fuel.

Quite likely it's just "varnished" up from years of use and needs a little TLC.  I would recommend getting our SR rebuild kit, it will be the most complete/correct in this industry and the highest quality components.

I would also check the mechanical and vacuum advance in the distributor to make sure they are both working correctly.  Lacking timing in the engines load/speed range will also cause the same symptoms as being too lean.....Cliff

Offline Brboles

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Re: Quadrajet has more power when choke is on
« Reply #7 on: January 06, 2019, 03:22:13 PM »
I’m sorry I didn’t mean to explain it that way. The idle mixture screws do have an effect on the engine and carb but it just doesn’t seem to make a difference with my problem.
« Last Edit: January 06, 2019, 03:29:40 PM by Brboles »

Offline Cliff Ruggles

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Re: Quadrajet has more power when choke is on
« Reply #8 on: January 07, 2019, 04:30:16 AM »
I would still take it apart and install modern components and give it a good clean-up.

At that time remove the plug over the APT screw so you can access it without removing the airhorn.  Tap the casting for a 3/8" set screw (we will supply one for free with a kit if you ask for it)

Tune the APT until the engine gets the fuel that it wants/needs. 

Typically with this new fuel it will like about 5-7 percent more of it to be happy......Cliff