Quick Fuel Carb Problem - Chevy Nova Forum
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Old 14th-May-2010, 08:41 PM   #1
Marcellus
 
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Quick Fuel Carb Problem

I have an 830 Super Street Quick Fuel carb on my 427 SBC. Electric choke.

When I start it up it wants to load up and you have to hold it up in RPM for about 15 seconds and rev it to get it to clear out. After a minute or so it start to clean up and idle fine. The bowls are not leaking fuel when it sets form what I can tell in the sight glass.

The car is a 5-speed and when slowing down and putting in the clutch the car idles down to where it ALMOST dies before picking up idle again.

I have replaced the power valve and worked on the idle adjustment screws to no avail.

The car has a solid rolller cam at about .600 lift but seems to idle fine at 900 RPM (112LS helps) I have idle set at 1,000rpm right now to help the issue.

Any ideas?
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Old 14th-May-2010, 08:51 PM   #2
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Quote:
Originally Posted by Marcellus View Post
I have an 830 Super Street Quick Fuel carb on my 427 SBC. Electric choke.

When I start it up it wants to load up and you have to hold it up in RPM for about 15 seconds and rev it to get it to clear out. After a minute or so it start to clean up and idle fine. The bowls are not leaking fuel when it sets form what I can tell in the sight glass.

The car is a 5-speed and when slowing down and putting in the clutch the car idles down to where it ALMOST dies before picking up idle again.

I have replaced the power valve and worked on the idle adjustment screws to no avail.

The car has a solid rolller cam at about .600 lift but seems to idle fine at 900 RPM (112LS helps) I have idle set at 1,000rpm right now to help the issue.

Any ideas?
Do you mean when you start it up it's cold and the choke is working ?
If so the choke "pull off" needs to be adjusted to increase the opening of the choke door for the first 30 to 60 seconds or so.

If you mean you start up when the engine is hot then it sounds like a hot boil over problem.

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Old 14th-May-2010, 08:56 PM   #3
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Quote:
Originally Posted by RED67 View Post
Do you mean when you start it up it's cold and the choke is working ?
If so the choke "pull off" needs to be adjusted to increase the opening of the choke door for the first 30 to 60 seconds or so.

If you mean you start up when the engine is hot then it sounds like a hot boil over problem.

Yea I have worked on the choke a bit but I am not sure that's the whole issue. It puffs black smoke and smells like it is running way rich, even if I start it cold and it is 75 degrees outside. Maybe I just need partial choke even then.

It doesn't do it when it's hot.

The choke doesn't explain the stumble coming down in RPM back to idle either. It opens all the way fairly quick.
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Old 14th-May-2010, 09:23 PM   #4
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Originally Posted by Marcellus View Post
Yea I have worked on the choke a bit but I am not sure that's the whole issue. It puffs black smoke and smells like it is running way rich, even if I start it cold and it is 75 degrees outside. Maybe I just need partial choke even then.

It doesn't do it when it's hot.

The choke doesn't explain the stumble coming down in RPM back to idle either. It opens all the way fairly quick.
OK.First things first.Electric chokes come on even when hot.
The choke pull off affects only the first 30 seconds or so and is the biggest problem with electric chokes when not adjusted properly.
The pull off is adjusted with a screw at the base of the pull off piston.Screwing it in limits piston travel,,,backing it out increases pull off piston travel and opens the choke door,,more
Some time this little screw is covered/sealed with white teflon,,,dig it out to adjust.
Best/fastest way to adjust is when the engine is cold and off,floor the throttle once and release it back to set the choke on fast idle.Have someone crank the engine with you looking at the carb choke door.Don't "work" the throttle while doing this.If the engine starts and runs rich turn the pull off screw in slowly,opening the door, untill the engine clears up.Do this within 30 to 60 seconds,,,,before the engine warms up.
After 60 seconds the electric heater will cause the bi-metal coil to begin to open the door.
Your idling down hot is another issue Tell us more about that.

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Old 14th-May-2010, 09:34 PM   #5
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Originally Posted by RED67 View Post
OK.First things first.Electric chokes come on even when hot.
The choke pull off affects only the first 30 seconds or so and is the biggest problem with electric chokes when not adjusted properly.
The pull off is adjusted with a screw at the base of the pull off piston.Screwing it in limits piston travel,,,backing it out increases pull off piston travel and opens the choke door,,more
Some time this little screw is covered/sealed with white teflon,,,dig it out to adjust.
Best/fastest way to adjust is when the engine is cold and off,floor the throttle once and release it back to set the choke on fast idle.Have someone crank the engine with you looking at the carb choke door.Don't "work" the throttle while doing this.If the engine starts and runs rich turn the pull off screw in slowly,opening the door, untill the engine clears up.Do this within 30 to 60 seconds,,,,before the engine warms up.
After 60 seconds the electric heater will cause the bi-metal coil to begin to open the door.
Your idling down hot is another issue Tell us more about that.

Thanks for the choke info I will try it.

The idling down issue is like this.

Driving say 45mph in 4th gear about 2,000rpm. Coming to a stop sign, push in the clutch apply brakes, engine idles down to say 500rpm stumbles alomst dies, corrects itself then starts idling at 1,000. The faster the RPM you do this the worse.
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Old 14th-May-2010, 09:50 PM   #6
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Originally Posted by Marcellus View Post
Thanks for the choke info I will try it.

The idling down issue is like this.

Driving say 45mph in 4th gear about 2,000rpm. Coming to a stop sign, push in the clutch apply brakes, engine idles down to say 500rpm stumbles alomst dies, corrects itself then starts idling at 1,000. The faster the RPM you do this the worse.
What if your driving 50 MPH and just push in the clutch and let it idle,,,,what happens then?

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Old 14th-May-2010, 09:52 PM   #7
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What if your driving 50 MPH and just push in the clutch and let it idle,,,,what happens then?

The same. I was just giving an example.
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Old 14th-May-2010, 10:18 PM   #8
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You need to adjust the idle mixture screws.
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Old 14th-May-2010, 10:24 PM   #9
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Originally Posted by Marcellus View Post
The same. I was just giving an example.
It could be a number of things but sounds like it's pulling too much gas from the transfer slots.Raising the idle may have made it worse.
Just thinking out loud,,the over rich condition,,,both hot and cold could be because the butterfly blades are up into the transfer slots with the chokes fast idle cam and as you let off from cruise speed.After the engine burns this gas it idles fine on the fuel supplied from the curb idle hole under the plate.
I'm sure you've seen all the articles about drilling 3/32" holes in the plates to "drop",,adjust the plates more closed at idle to not expose so much of the transfer slot.I don't like the holes but the article explains the theory.I like to put epoxy in the hole to raise the slot,,,it's easy,you measure down to the bottom of the slot with a machinest rule before/after.A little goes a long way.If your slots are more than "just peeking" under the plate their exposed too much.This will cause an off idle stumble on "gentle" accel also.Does it do that?

You're sure the floats are set properly ?? Fuel pressues not too high ? Do you run a vacuum advance?

We've assumed a rich condition a vacuum leak could cause these same symptoms too when driving not the choke problem.

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Old 14th-May-2010, 10:33 PM   #10
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Quote:
Originally Posted by RED67 View Post
It could be a number of things but sounds like it's pulling too much gas from the transfer slots.Raising the idle may have made it worse.
Just thinking out loud,,the over rich condition,,,both hot and cold could be because the butterfly blades are up into the transfer slots with the chokes fast idle cam and as you let off from cruise speed.After the engine burns this gas it idles fine on the fuel supplied from the curb idle hole under the plate.
I'm sure you've seen all the articles about drilling 3/32" holes in the plates to "drop",,adjust the plates more closed at idle to not expose so much of the transfer slot.I don't like the holes but the article explains the theory.I like to put epoxy in the hole to raise the slot,,,it's easy,you measure down to the bottom of the slot with a machinest rule before/after.A little goes a long way.If your slots are more than "just peeking" under the plate their exposed too much.This will cause an off idle stumble on "gentle" accel also.Does it do that?

You're sure the floats are set properly ?? Fuel pressues not too high ? Do you run a vacuum advance?

We've assumed a rich condition a vacuum leak could cause these same symptoms too when driving not the choke problem.

When talking about the transfer slots are you talking about the primary or secondary slots?

The primary slots show about 1/8" right now. The secondaries show none of the transfer slot.
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Old 14th-May-2010, 10:44 PM   #11
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When talking about the transfer slots are you talking about the primary or secondary slots?

The primary slots show about 1/8" right now. The secondaries show none of the transfer slot.
About 1/8" ?? It'll run like $h*! at .040 !

The secondaries won't be showing.The primary slots shouldn't show more than .010"

Does the car have an "off idle" stumble ??
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Old 14th-May-2010, 10:45 PM   #12
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You should have about .040" of the slot uncovered when looking from under the carb. I do not like the idea of drilling the holes either.
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Old 14th-May-2010, 11:08 PM   #13
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its a stick car

its a stick car ,, soo ,,, it doesn't require as much throttle plate opening to achieve idle speed ,, so i doubt its having an issue with the transfer slots

when the throttle is slammed shut , and put in neutral , its rotating mass is less than an automatice so it loses engine speed quick ,

holley made these available for factory equipped stick cars to combat this problem , it eases the throttle blades shut to give the carb time to recover to idle fuel requirements

http://www.summitracing.com/parts/HLY-11-4/

u might try a PCV valve too ,, if you don't want to install that on your carb ,,

Last edited by levisnteeshirt; 14th-May-2010 at 11:13 PM.
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Old 14th-May-2010, 11:52 PM   #14
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u might

thought about this a lil more ,, u might try a lil bit less initial timing , and open the throttle more to get it to idle the speed u want , then reset the centrifigal advance for the total u want
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Old 15th-May-2010, 12:00 AM   #15
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Quote:
Originally Posted by tbills66 View Post
You should have about .040" of the slot uncovered when looking from under the carb. I do not like the idea of drilling the holes either.
A 427 needs alot of air to idle requiring alot of throttle blade opening just to do it and getting into the transfer slot, the holes do help with this situation. This idea seems to cause alot of controversy and I never really likes that idea either, but if my new Pro Systems 950 has the drilled then it's OK with me

Not saying that's the fix here but I was surprised when I saw them drilled...
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