Idle issue with 63 chevy

[Mack B]

Ill try to be as detailed as possible,I'm no mechanic, but have been around old piles of crap all my life and can handle most tasks under the hood. the weather here is in the low 70's and has been every time I've had the truck out. it's a 283 small block with unknown internals but runs fine on 87 octane usually has a mild lope when it's cold, edelbrock 600cfm carb, and summit hei ignition. It's been running fine till the last time I drove it, it was idling rough (sounded good really ) but the idle speed was low and tried to die just off idle. This was last weekend, this evening I had a chance to mess with it, I tried turning the idle speed up, but it would not increase. After turning the screw if I patted the gas the idle would stick high for a few seconds then fall back low. After that failed I richened up the idle screws a bit and that helped smooth it out a bit. I then adjusted the timing from 8 degrees advance to 6 degrees at idle (made no difference). It did get warmwhile i was playing with it around 195 degrees (i know this is no where near over heating, but the highest ive ever seen the gauge scince ive had this truck is 180 in the middle of summer) My question is did I mask a problem by fattening up the idle mixture? What would cause it to need to be adjusted out of the blue? Anything else that would cause these symptoms I should check?
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[Rich 5150 69]

Have you ever rebuilt the carb, check the gas filter, you have one I`m assuming, start with a ne w fuel filter, then get back to us....

[Mack B]

Thanks for the reply, the carb was installed new less than a year ago, I changed the filter then, not to say it hasn't gotten clogged up tho, I'll check it out
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[Rich 5150 69]

When you remove your filter, before you install the new one crank the engine over with the fuel line open into a container, two reasons check condition of fuel pump and clear out any debris that might be in there, into a container you can see in. There may be junk in the tank, clogged sock ( screen on the line in the tank )...

[Rufton]

When tuning idle A/F mix screw I turn screw CW till idle gets rough.
I mark mix screws w/ white out at leanest smooth idle.
Then I turn CCW till rough idle and note how many turns from lean idle to rich idle.
I usually idle near lean limit and I run coldest plug engine will tolerate.

I would pull some plugs and make sure they are correct color; near white to tan w/o deposits.

I would do a quick linkage binding check.

[Mack B]

Originally Posted by Rich 5150 69

When you remove your filter, before you install the new one crank the engine over with the fuel line open into a container, two reasons check condition of fuel pump and clear out any debris that might be in there, into a container you can see in. There may be junk in the tank, clogged sock ( screen on the line in the tank )...

Thanks sir ill do that and report back tomorrow

Originally Posted by Rufton

When tuning idle A/F mix screw I turn screw CW till idle gets rough.
I mark mix screws w/ white out at leanest smooth idle.
Then I turn CCW till rough idle and note how many turns from lean idle to rich idle.
I usually idle near lean limit and I run coldest plug engine will tolerate.

I would pull some plugs and make sure they are correct color; near white to tan w/o deposits.

I would do a quick linkage binding check.

That's the procedure I followed on the idle mixture as well, it just seems odd to me it would have came out of adjustment out of the blue. Linkage moves free, the problem of it temporarily idling high after adjusting the idle speed went away with adjusting the mixture. Ill pull the plugs tomorrow and get some pics, thanks for your help!
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[geezer#99]

Bump your timing back the other way. Try 12* to start. Hook your vac advance to manifold vacuum. Idle will speed up. Turn down idle as low as possible then adjust mixture screws.

[Rufton]

Some carbs can have out of the blue problems if they sit long enough for gas to go bad.
Autolite 4 BBL and Stromberg 2 BBL can sit a couple years w/o problem.

My new Edelbrock sat a couple years and it gave me a fit tuning idle. After sufficient hair pulling I rebuilt it and it's has worked perfect ever since.

Does it smell rich when misbehaving?

[Mack B]

Originally Posted by geezer#99

Bump your timing back the other way. Try 12* to start. Hook your vac advance to manifold vacuum. Idle will speed up. Turn down idle as low as possible then adjust mixture screws.

Played with the timing today, it responded best at 10 degrees ( I measured this by the ability to chirp the tires in fourth lol) the idle surged bad when I switched to full manifold vacuum, does this mean anything? I swapped it back.

Originally Posted by Rufton

Some carbs can have out of the blue problems if they sit long enough for gas to go bad.
Autolite 4 BBL and Stromberg 2 BBL can sit a couple years w/o problem.

My new Edelbrock sat a couple years and it gave me a fit tuning idle. After sufficient hair pulling I rebuilt it and it's has worked perfect ever since.

Does it smell rich when misbehaving?

This truck gets drove pretty regular other than a few month period last summer while I was injured (wear your safety glasses kids) however I did fill up the last time I drove it before this started. While tuning it last night it definitely smelt rich, I came inside smelling like I had been on a tractor all day.

First thing today I changed the fuel filter, fuel pump appears to be in good working order. Fired it up and greeted with a rough idle after it warms up, again I fatten up the mixture and it smooths out. After I got it to idle I adjusted the timing readjusted the mixture and test drove it pretty hard, it runs good and strong, no hiccups or hesitations, rattles, pings, has no problem breaking the tires loose or pulling to 6000rpm. Keep in mind I did this same routine last night,
Just to have do it again today, eventually the screws will back all the way out? Lol. I guess I'll try again in the morning and see if it happens to stay "fixed" this time. Here is a pic of a plug pic is bad but it's near white, electrode is tan

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[geezer#99]

If it surged when you went to manifold vacuum it might mean you have too much timing added with the vacuum pot. Run whatever your motor likes.
The mixture screws shouldn't back out. Do you still have the tension springs on them?
Your plug looks alright.

[Mack B]

I thought about that and once I get this squared away ill try the manifold vacuum and tune the advance to see if it performs better, drivability is good as is but economy isn't great. I was half joking about the screws backing out, meaning if I have to adjust every time I start it eventually ill be out of room to adjust. <--I know that isn't an option. I appreciate your help and advice, if this persists tomorrow ill update again. Thanks to all!
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[Rich 5150 69]

You might want to check for a vaccum leak, a can of carb cleaner shoot at the base of the carb, maybe just check carb bolts for tightness, and or manifold leak, hose leak to dizzy or booster if you have power brakes.

[Rufton]

Your plug looks great.
Keep in mind plug color can change.
Plug can be black after rich idle but turn white again after lean cruise.
I'd pull one plug after next time it idles bad to make sure idle isn't rich.

If you over advance timing you can destroy engine in a heart beat. 6000 rpms is starting to get scary because you are stress testing engines quality and design. My engine is designed for 6500rpm but I'm not brave enough to test.
Check all in timing at about 2500-3000rpm to make sure it does not go above design; many street engines like all in timing of 32 to 38.

[Rufton]

Bad PCV can cause out of the blue crappy idle.
While checking PCV I like to check the hoses as well.

I don't remember if you verified choke is full open.

[Mack B]

That plug was after a long idle, after getting it running smooth. I should have noted I first thought vacuum leak and sprayed it with wd40 while running. And verified choke was open..
Total advance is 42 in @ 3000, it doesn't ping or rattle so I figured I'm ok there, but can see limiting the vacuum advance wouldn't be a horrible idea. I admit I beat on the old girl harder than I should, all projects in the past have been on the ragged edge of streetability and this is my first effort at a solid driver, and well....some habits are hard to break
Back to today it crunk up fine and after warming up, had a good idle and was drivable, so it either just randomly needed adjusting two days in a row, or it fixed itself, or its gonna show up again at some point, I know what I expect to happen
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[Rufton]

42 advance is pretty aggressive.
I'd like to beat on mine but don't wanna risk any more projects.
If I had Leno's mechanics it'd be a different story.

Any chance you got a tank of bad gas?

[Mack B]

It's very possible, I did fill up the last time out. Keeping fingers crossed at this point. I appreciate your help/advice
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[nxtruck]

One other thing to think about, which may or may not be causing you trouble, is the fact that the Edelbrock carbs can't tolerate as much fuel pressure as, say, a Holley can. I found this out the hard way on my son's '65, as it had a rich idle issue that I couldn't tune out of it. After doing some research on Edelbrock carbs, I learned that they are calibrated to run with no more than about 5-5 1/2 lbs. of pressure. The stock mechanical pump was putting out between 7-8 lbs. at idle, so I threw a Holley blue regulator on it, backed the pressure down to 5 lbs., and then it was responsive to idle screw adjustments. Like I said, this may not be an issue for you, but it's something to keep in mind.
Good luck with yours!

[Rufton]

Originally Posted by nxtruck

One other thing to think about, which may or may not be causing you trouble, is the fact that the Edelbrock carbs can't tolerate as much fuel pressure as, say, a Holley can. I found this out the hard way on my son's '65, as it had a rich idle issue that I couldn't tune out of it. After doing some research on Edelbrock carbs, I learned that they are calibrated to run with no more than about 5-5 1/2 lbs. of pressure. The stock mechanical pump was putting out between 7-8 lbs. at idle, so I threw a Holley blue regulator on it, backed the pressure down to 5 lbs., and then it was responsive to idle screw adjustments. Like I said, this may not be an issue for you, but it's something to keep in mind.
Good luck with yours!

Another thing to do If pump pressure is overpowering shut off valve. Set float to lower elevation so it will exert more force on shut off valve. This will increase valves effective shut off pressure.

While setting float it is good to inspect condition of shutoff valve.

[Mack B]

Nxtruck that is the best avatar on this site! Your truck looks awesome with the wheels up! I drove this thing around a bit today and its running good now....I don't know? Ill just be keeping a screw driver in the truck for a while
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[nxtruck]

Thanks for the compliment! Glad to hear yours is running good now. Maybe a load of bad gas?

[Gianyveedub]

My 235 had a bad problem with this for a while. It turned out that the HEI I had needed a rebuild. How old is your HEI?

[Rufton]

Originally Posted by Gianyveedub

My 235 had a bad problem with this for a while. It turned out that the HEI I had needed a rebuild. How old is your HEI?

I converted one engine to petronix electronic ignition and its fine but minor wiring mod was required. I'm a little uneasy if it fails on trip; you could carry removed points to convert back in emergency.

I'm still running points in 2 other engines. Pretty sure points weren't changed for over 20 years in the truck. The points tend to be reliable for decades in low mileage applications. Cool thing is you can keep $5.00 spare points/condenser in the glove box.

I'd go electronic for >5000 rpm performance application.

[Mack B]

Originally Posted by Gianyveedub

My 235 had a bad problem with this for a while. It turned out that the HEI I had needed a rebuild. How old is your HEI?

It's a summit branded one I put on a year ago at the same time I changed the carb. I had allsortsa drivability problems when I bought the truck.
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