Lars just fixed my carb. It idles a little better and is crisp off the line. However, the idle is still not how it should be. Putting a vacum gauge on an intake port the needles vibrates 1/2 lb from 16 in both directions. The cam is stock so the rough idle is not due to large cam. Have checked for vacum leaks, plugged all ports with no noticeable change. Just read an article on tuning with a vacum gauge
http://www.centuryperformance.com/va...alve%20Guides: and it best describes my engine vacum at idle as number 2. Ignition appears fine and no big cam so I am down to the other two possibilities. Off idle no missing runs perfect, only at ilde both out of gear and in gear it is more prominent. Any advice on how to check for sticky valves of hydraulic lifters bleeding would be appreciated. I am at wits end going round and round with this idling dilema L82 1980 auto

 

Do a compression test. It could be a valve train problem.

BigBlockk

Later.....

 

Lots to check. Start with the easy stuff --- problem could be electrical (you're certain you have no vacuum leak, correct and your carb is now rebuilt). How old are the plugs, wires, coil and distributor. Try advancing and retarding the timing to see if that changes anything. Chect the EGR valve to see if it might be frozen in the open position --- that would screw up your idle. As far as the engine internals, I think if you ran a compression test and a leak down test, then you would have a better handle on what's going on inside your engine. How many miles do you have on your engine and how hard has it been run?

Eliminate the easy stuff first, before you jump to the conclusion that it is a valve problem.

Good luck

 

Did a compression test. All electrical parts are fairly new. New mallory ignition along with plugs and wires. Plugged all ports on manifold and carb and checked for vacum lea around carb base and manifold base. no change in idle. No change in idle quality retarding or advancing timing, New EGR valve, I think comp test had around 150 with no drastic difference between cylinders. 52,000 not driven hard usually cruising around town, but will get on it on the interstate. not over 75
Tore engine down last winter, pistons looked good, had my brother look at them and he gave thumbs up, he's a mechanic. Had heads cleaned and checked out, new performer intake manifold. Basically a upper block rebuild. The only thing I can think is I may need to redo the valve adjustment. They may be to tight and not allowing the heads to operate properly giving me that rough idle. Looking for confirmation to my conclusions. Lars found a bunch of things wrong with my carb. But after rebuild he said it ran great on his engine and it does run better on mine. However, it still feels like it's missing a idle, off idle it motors.

 

Is your fuel bad/old?
This will cause bad idling and you can't tell at high speed.

 

Did you inspect cam?
Did you remove lifters?
If so, did they go back in their original bores.?
What was done to heads, shaved?
Did you use end gaskets on intake set when assembling?
What was vacuum reading before teardown?

 

Is this the commecially-rebuilt carb with mixture screws at 10 turns?

 

Perhaps I misunderstood.

 

OK you have a rough uneven idle and you seem to have checked out the easy stuff. How old is the gas in the tank and could it be old with a little water in it? Drop in a can of Gumout in the tank and run out a full tank before you start ripping the engine apart. I doubt you over-tightened the valves --- this is hard to screw up. You said you did an upper block rebuild last year ---- did you have a rough idle before you did the rebuild? Exactly what was done when you did the upper block rebuild and what was done to the valve train --- did you change lifters, cam, springs, rockers ---- did you go from 1.5 to 1.6 on the rockers. Exactly what was done here.

 

Yeah Lars it is the 10 turn carb. I have not messed with your setup any because you said it ran fine on your engine after rebuilding. Tried to look for vacum issues but everything seems to be working. Removed all port lines and plugged them and could tell no significant difference. It is idling better than before rebuild, however it still has fluctuation when idle and more significant when in gear and foot on brake. New tank of gas. Had the rough idle before rebuild, figured the cam may have been replaced based upon the local guys input. However, it was the original GM cam. Replaced with same spec cam to be safe. Put in new lifters, used same push rods and rockers, new intake performer manifold because original had cracks around carb, had heads shaved and cleaned. It will idle down fine when messing with timing. However it just seems to be missing sporatically. Adjusted valves and now get 17lb but the little fluctuation of 1/2 lb oil pressure gauge also fluctuates with the engine stumbles. Any good ways to make sure all plugs are firing everytime. Some times when I check timing with the timing light the light doesn't light when it is supposed to but it is not in time with the stumble.

 

Missed this one
Did you use end gaskets on intake set when assembling?
But you had a miss before the rebuild....
After shaving the heads, it's tight with the end gaskets and could have bottom vacuum leak.

An oscilloscope will show if cylinders are firing evenly and continually.

Have you run it and taken plug readings?

A little check of adjustment on the valves won't hurt.

So what carb are you using a commercial or a Lars?

 

Used intake set. Have not taken plug readings. What is that procedure. Readjusted valves this mornig helped some I think. Really didn't get a chance to mess with it had to leave. Had my carb rebuilt twice before Lars went throught it and fixed it properly.

 

Here is a link to plug readings. Haven't read it, but pics looked okay.
It would show a weak or problem cylinder.
http://www.4secondsflat.com/Spark_plug_reading.html
Try running with the vacuum advance hose unplugged from the dist to test. Test the diaphram too.

An oscilloscope may still be the easiest and would test the consistancy of the hei output.

 

Check the movement of the rocker arms shakey vacuum is an indication
of valve train problems . Hate to say it but i think your camshaft has a lobe or 2 ground off. Seen it many times in engines of that vintage the lowest mile 1 had 12k miles

 

Rocker arms seemed to perform fine. All lobes were moving this morning. Adjusted them this morning with engine running.

 

What is the proper spark plug gap for a 1980 L82 3 spd auto?

 

OKay... That carb has had the idle circuit modified by the commerical builder, and it's not set up exactly as it should be due to those mods, as noted on my note to you earlier. The idle circuit, even at 10 turns out, was slightly lean during my testing (ran at 15:1 instead of 14.7:1), and this can cause a slightly rough idle. There wasn't anything I could do with that carb to correct it. You can back those screws out another 2 turns max to see if it smooths it out a tad. Also, if you'd like to verify that the carb idle circuit is too lean I can send you out one of the Forum Loaner carbs to test on your setup. Let me know.

Run it at .045"

 

Lars,
That would be great. Do you have my address still?

 

Can someone elaborate on a '10-screw carb'. Mine has a 'rebuilt by Holley' decal on it and I have no idea if its setup right for my car.

 

Laes can give you the exact details. However, based upon what he told me the screws in my carb are aftermarket and instead of 4 turns they need to be 10 turns to allow proper idle. But the carb still has a rough idle to it so he suggests I go to 12.