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Discussion Starter #1
Ok, I've posted another topic about this, but I can't seem to get it straight.

The Quadrajet is on a 1986 Chevy C10 (original carb). I rebuilt it, and since then I'm having this cold-start problem.

When I start it, it idles very rough and just kinda chug-chug as it idles. As it's idling, it's backfiring through the exhaust quite often. Not too loud, just a couple of firecrackers. Once I drive it, the problem goes away (since the motor is warming up).

To me, the backfiring tells me that it's too rich. I did, however, shorten the rod for the choke pull-off, and I think it made it worse (reduced the chock plate to airhorn gap from 1/8" to slightly under 3/32". It SEEMED to backfire more, but I wasn't sure.

Since it's been getting very cold here (below freezing during the morning), it's pretty tough to start the thing because of this problem. Almost wear the battery down trying to get it to start.

What do you guys think?

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1969 Base Camaro
Vortec 355, Perf. RPM, Demon Carb., TH-400
All sheetmetal is NOS GM
See my webpage at: http://www.geocities.com/compuboy007/
 

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Don't overlook a possible ignition problem. Could be that the choke is messed up, but an ignition mis-fire is causing you to chase your tail.

-dnult
 

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If you haven't done it already, check the pull-off diaphragms with a hand vacuum pump and make sure they don't leak down. If they leak replace them. Also if you had the choke thermostadt out make sure the flat tang on the coil is between the two fingers on the actuator inside the housing. I don't think the '86 choke thermostadts were adjustable. They had a key that fit into a groove on the housing. Make sure the key is in the groove. I'm going from memory here so be patient. There should be two pull-offs. One mounted toward the rear passenger's side and one on the front passenger's side with a rod that goes to the secondary air valve. There should be an adjustment screw above the choke thermostadt housing. This screw can be used to set the initial break on the choke. This is where the hand pump comes in handy. I use this screw to set the gap to whatever the book says and then set the gap from the rear pull-off about 1/32 to 1/16 wider. Just pushing the diaphragms in with your finger doesn't give the same results. The backfiring is more than likely the plugs getting wet and fouling. Once they've been soaked three or four times I replace them. I haven't had much luck with cleaning and regapping.

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'69 RS Camaro
355 5-speed 4.11
 

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Discussion Starter #4
Dnult-
That's a good point. Thankfully, I just got the ignition in working order not too long ago. Thanks for the tip.

1 2RUN-
Sounds like you know more about these Q-jets than I do.
About the choke deal, you said to have the coil tang in between the two fingers in the choke housing. I just remember one finger, and it had a little piece of plastic around it for whatever reason. Maybe I'm not understanding correctly.
I did get the keyway on the choke fitted correctly. I was wondering if I should file off the key so it's adjustable...
I did check the vacuum diaphram with a pump, and it didn't leak down. Also, my carb only has one diaphram, which controls both the choke and the secondary air valve.
I don't remember seeing an adjustment screw like you had mentioned, but I'll check it out when it's daylight.

Thanks for the help guys, I'll keep you posted.

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1969 Base Camaro
Vortec 355, Perf. RPM, Demon Carb., TH-400
All sheetmetal is NOS GM
See my webpage at: http://www.geocities.com/compuboy007/
 

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Silver69,
You can drill the rivets out and replace them with screws to make your choke adjustable.

You may have to grind the notch off also with a dremel tool on the choke housing if that is there.

Is the choke a stovepipe type? If it is you can take a newer model carb with an electric choke and convert which is what I did to mine. It bolts right in place. I'm using a Q Jet from a 79' Vett.



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Drew

99' GMC P/U
69' Camaro X-11 350/T350,AC,PS,PB, 12 Bolt
96' 17' CC KEY WEST w/85 Yamaha (has shark fins on the sides like the 69')
 

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I kind of have the same problem, but without the backfire. But when mine does this it's time to do an oil change on it. Looks like the oil is to thick or something and it won't stay on till I've cranked it six or more times.
 

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The actuator lever inside the choke housing should have a slot (looks like a fork) in it that the thermostadt coil tang slides into so it can pull the choke shut as well as pull it open. That's what I was refering to as fingers. If it has an adjustment screw it wiil be part of the front pull-off's actuating lever that the secondary air valve rod attaches to. Some carbs had two pull-offs, some only have one. One more thing I forgot to mention about Q-jets. They are notorious for leaking under the fuel bowl where the primary fuel bosses are drilled and capped. It is highly recommended that you seal these bosses with epoxy when you have the carb apart. If they are leaking it will drain the fuel bowl into the intake overnight and flood the engine the next time you start it.

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'69 RS Camaro
355 5-speed 4.11

[This message has been edited by 1 2RUN (edited 10-29-2002).]
 

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Discussion Starter #8
Ok, here's the deal.

I did have a little problem with the choke, but I fixed that now. Didn't fix the main problem, however.

But I was able to determine the choke was opening too slowly. When it was doing its rough idle-'n-backfire problem, I simply opened the choke plate with my finger and it ran smoothly.

Now the question is, how do I fix that? I guess I could grind the keyway off (I already drilled out the rivets and replaced them with screws). Do I have to mess with the choke pull-off diaphram?

It seems as if it only needs the choke plate to be closed while it's being started. Once it starts, it needs it to be 1/2-2/3 of the way open in order to run right.

Suggestions?

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1969 Base Camaro
Vortec 355, Perf. RPM, Demon Carb., TH-400
All sheetmetal is NOS GM
See my webpage at: http://www.geocities.com/compuboy007/
 

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OK, the choke pull off is used to keep the engine running once it starts.

Using the choke coil housing since you've drilled the rivets out you should be able to move the coil housing to adjust the choke. You may have to grind the notch as I posted earlier.
I would set the choke to close fully under the least amount of pressure from the coil spring. Make sure the butterfly moves freely and move the choke coil spring, you should see the butterfly move back and forth.
The older style stove pipe choke is slower to respond and creates longer warm up times, especially in cold weather. This causes more raw gas to go in the oil pan. That's why it is nice to convert to the electric choke, it is much more reliable.

If you post the carb # I may be able to look up what the choke pull off setting is. The number is on the side of the main body and may start like 170XXXXX.

You are correct in your thinking of how the choke works.

Hope this helps.

[This message has been edited by drew69 (edited 10-30-2002).]
 

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I believe what happens is the spring sets the choke for starting then, once the engine starts, the choke pull-off pulls the choke plate open against the resistance of the spring.

So, the spring needs to be wound up for starting, as in the plate "snapping" shut.The linkage for the choke pull-off needs to be bent to adjust the opening when vacuum is applied.

Read the instruction sheet from an overhaul kit for setting the opening by the choke unloader.

The vacuum pulls against the spring. As the bimetal spring heats up, the choke opens.

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Everett "OBJECTS IN THE MIRROR DISAPPEAR UPON RAPID ACCELERATION"
 

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Discussion Starter #11
Well, it was 6 degrees out this morning here in Ellensburg, I started the truck, and ran absolutely terrible. It even died at a stop sign.

So, I bent the heck out of the choke pull-off rod. This way, when vacuum was applied to the diaphram, it opens the choke just about all the way (it takes about 1.5 seconds to get there, it doesn't 'snap' open).

Starts and runs great when cold now. I don't know if this was the right way to go about things, but it worked.

Now I'm curious why I had to do this in the first place...it was fine before I rebuilt the carb...remember when your wife says "why fool with it if it runs fine??", yeah, I don't wanna hear that from any of you guys! Ha!

Thanks guys.

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1969 Base Camaro
Vortec 355, Perf. RPM, Demon Carb., TH-400
All sheetmetal is NOS GM
See my webpage at: http://www.geocities.com/compuboy007/
 
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