My idle sucks

[Mark1968]

It's not that she won't idle, but it is either too high or two low.

1979 k20 very stock 350 and lots of vacuum lines. No vacuum leaks that I can see. Reset the idle mixture screws at about 3 turns out each. Idle speed screw is just barely touching. This gives me the best quality idle, but it's about 1k rpm and when I shift from park to reverse or drive I get the big clunk.

When I turn the screws in about half a turn each, I get 6-700rpm, not as smooth an idle but no driveline clunk. It also does not want to start in the morning set this low.

I'm looking for a balance between the two. Also how much of this emissions crap can I throw away? All of it is hooked up.

 

[Mark1968]

Stock Q-jet BTW. I'm also not sure what the timing is set at because I can't get an eyeball on the timing tab. I think it should be on the right side but i dunno.

 

[rdn2blazer]

It's not that she won't idle, but it is either too high or two low.

1979 k20 very stock 350 and lots of vacuum lines. No vacuum leaks that I can see. Reset the idle mixture screws at about 3 turns out each. Idle speed screw is just barely touching. This gives me the best quality idle, but it's about 1k rpm and when I shift from park to reverse or drive I get the big clunk.

When I turn the screws in about half a turn each, I get 6-700rpm, not as smooth an idle but no driveline clunk. It also does not want to start in the morning set this low.

I'm looking for a balance between the two. Also how much of this emissions crap can I throw away? All of it is hooked up.

Unfortunately, the late 70's and into the 80's WAS the worst years for "smog" vehicles. Being able to get rid of smog stuff totally depends on the smog laws in your state. I don't know Ohio so you'll need to look into that unless your building a dirt toy only. As far as vacume leaks, you can't "see" them, you need a vacume tester and will have to check every line. Replace any and all cracked or dried out lines.

As far as carb setting, if there are other issues like vacume leaks, tuning the carb won't yield the results you're after until those are adressed and fixed first. It's like tightening a nut without having a wrench on the head of the bolt. It ain't gonna get tight no matter what. Are you sure there arn't timing issues? Rough or low idle can be more then just vacume leaks and carb settings.

 

[rdn2blazer]

Get a manual and make a check list of how things should be setting and tuning wise and go down the line. Carb may need rebuilding. How grimmed up is the motor? Pressure wash the motor and engine bay good and dry with air hose then start your list and fix and learn as you go.

 

[Mark1968]

No smog in this part of ohio, even so this thing is 25+ years old.

The way I've been checking for vacuum leaks is spraying lines with carb cleaner or wd40 and listening for a change in speed. Most of the lines are new.

While taking this picture I found the timing tab. much easier to see during the daytime I think.

 

[Mark1968]

So as it was, I had maybe 20 degrees initial timing. I pulled the dist. out and moved it one tooth then spun it till i got down to 8.

Specs on the sticker call for 8 but it seems to run better at 10 degrees. idle is a little faster and I get about an inch more on a vacuum gauge.

So which is it? I'm tempted to leave it at 10.

 

[Blue85]

If adjusting the idle screws does something, that's a good sign. You want it set for maximum vacuum, which is another way of saying you want the mixture setting that gives the highest idle speed. So you go in iterations, adjusting the mixture screws to increase idle and adjusting the idle speed screw to bring it back down to spec (650rpm?). When you're done, this will be the maximum vacuum the engine can make at idle. It's almost always a lot richer than the factory setting. Fuel distribution is anything but ideal with a carb and wet manifold, so the engine appreciates extra fuel. Emissions are worse, though.

 

[Mark1968]

Got it. I'll give it a shot tomorrow after work.

 

[diesel4me]

You might want to see where the vacuum advance hose is connected too,some engines in the early 70's used manifold vacuum to the advance unit instead of ported vacuum,that can affect the idle speed and quality..