Throttle return and Choke valve issue - Chevelle Tech
Troubleshooting Diagnosing problems done here.

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post #1 of 5 (permalink) Old Apr 21st, 19, 9:19 AM Thread Starter
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Paul
 
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Throttle return and Choke valve issue

Need a little help I am new to carbs and I am for sure having an issue with throttle return and I might have an issue with my choke valve. First the throttle return.

Yesterday when I was driving I got a little heavy on the gas I think I heard a pop and when I let up off the gas the throttle wouldn't return to zero unless I got my foot under the pedal unless I pulled up on it with my foot. Thought maybe the throttle return spring broke but when I got home and got the air cleaner off it was there and looked fine (If a little sketchy, see pic. I am not sure but I don't think it should just be on a bolt like that.) but still have the issue with the throttle not completely closing. I put a heavier spring on it and it working correctly right now but something is still bothering me about it. Is there another spring some where in the throttle line/linkage I am missing.

Second while looking at the Throttle issue I noticed that it is not possible for the choke valve to completely close. it seems like the little arm on the electric choke is hitting structure on the carb and not letting it close completely any one else have this issue? its a Holly 80457 7.

and from the look of the oil on my intake it looks like a compression check might need to be in my future.

Thanks
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post #2 of 5 (permalink) Old Apr 27th, 19, 3:15 AM
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Re: Throttle return and Choke valve issue

1. You should have dual throttle return springs, as supplied by GM on all of these vehicles when new.
1b. I dislike having the throttle cable or throttle linkage pulling in the same direction as the return springs. The cable and the spring(s) both pull the throttle shaft to the rear--increasing the wear on the throttle shaft and throttle bushing area of the baseplate. "I" would find a way to attach the return springs as closely as possible to where the throttle cable connects. Then the throttle cable and the return spring act in opposition, reducing pressure on the throttle shaft.
1c. I'd be checking the entire throttle cable and gas pedal assembly. A frayed throttle cable can cause the throttle to stick,
1d. Last time I had a Holley that wouldn't idle consistently, I found that the throttle plate screws had come loose. The throttle blades were shifting. I was very lucky one didn't slide entirely out and get swallowed.


2. I have no idea why the choke arm would hit "structure" on the carb. Sure it isn't hitting the fast idle cam? The throttle has to open enough to get the fast idle screw to clear the fast idle cam, before the choke can close fully.

3. Why aren't you using vacuum advance? You're throwing away fuel economy and part-throttle response.
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post #3 of 5 (permalink) Old Apr 27th, 19, 7:26 AM
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Hank
 
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Re: Throttle return and Choke valve issue

The choke plate is probably not closing all the way because the choke may not be set right or the fast idle screw may be hitting on the step of the red fast idle cam. With the car off push the throttle shaft back as if you were giving it gas and see if you can rotate the choke plate closed all the way and see if it stays there. When the car starts the choke plate should open about 1/8" to let air in. Now to the gas pedal cable it looks like the covering is missing from where it comes out where it mounts to the carb up to the other black covering that comes off the end of the cable that is connected to the throttle shaft. It actually looks like the broken part is inside the front black section. The cable could be fraying. I would get a new gas pedal cable just make sure you get the right length one. The spring looks like when the carb is closed there is no tension on the spring it should be showing gaps between the coils even at that point. Try shortening the spring a little bit. Another thing the rubber fuel line running up to the carb looks like it may be too big in dia. It should be 5/16 or 3/8" ID hose.

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post #4 of 5 (permalink) Old Apr 30th, 19, 12:58 PM
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Roland
 
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Re: Throttle return and Choke valve issue

It looks to me like you could get a throttle spring return bracket that usually attaches under the ignition coil and sandwich it between a combination of bolts and washers where the rinky dink bolt end set up currently is. IIRC, there were thermostat housings that had holes for return springs, but yours looks too far away for that. As for the oil control issue, I'd verify what PCV you're running first. Altitude and non-stock cams can wreak havoc in that department.

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post #5 of 5 (permalink) Old May 25th, 19, 8:28 AM Thread Starter
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Paul
 
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Re: Throttle return and Choke valve issue

Thanks for all of the reply's! This car is still very new to me and I am still learning about carbs and distributors. I come from the land of fuel injection and coil packs. I don't know why the previous owner did what they did. I am working to correct things as I find them and learn.

I did do a tune up a couple weeks ago and took the carb off to check and see if there was any oil in the intake and to clean up the carb a bit. I did notice that once I had the carb on the bench the throttle closed like normal. this is making me think that it could be due to an issue with the diaphragm for the vacuum secondary.

I forgot to check it once I first had it back on the car but after the first startup the problem returned. still running with the heavier spring. and will start looking for a new throttle bracket.

Thanks
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