Idle issues and running rich

[rhino2104]

Okay, so I have a 1976, 302, 3-speed that the idle is all over the place with. When it is warming up it idles rather high and after it has warmed up then it might idle high or it might idle low to the point of dying. When it is idling low and you rev it it takes quite a while for the idle to come back down.

It is also running pretty rich. I did put a rebuild kit in the carb which didn't really help the issues. The timing is set to 6° BTDC as per the factory recommendations. It does have after market exhaust but otherwise is completely stock as far as the engine goes.

 

[DuctTape]

There are other threads on this that I'd suggest searching for to get more details, but bottom line you have to go thru a troubleshooting process as there can be many causes of your symptoms,

Unless you know something is good or you suspect something is bad, follow this order:

Start by checking for vacuum leaks or lines wrong place, fuel delivery to carb, then spark wires and plugs, then distributor/coil (check cap, points or module, coil resistance check, timing, vacuum advance etc), then start tuning the carb.

When you start tuning the carb there are a bunch of sites that walk you thru it. For checking fuel pressure most parts shops these days will let you borrow a fuel pressure gauge for free. I do suggest getting your own vacuum gauge - they are cheap and useful. Timing light I think you can also borrow for free.

Oh, and there is something else that I've seen others talk about with regards to stock engines - it was just on a recent thread - good idea to hunt that thread down and read it.

 

[rhino2104]

I was chasing vacuum leaks with a can of carb cleaner spraying it around the intake until I got them all sealed up. Fuel delivery is a known good. New pump, tank, lines, and filter. Plugs and wires are brand new as well as the distributor cap, coil, rotor, and ignition module. The only thing that I haven't changed is the vacuum advance on it. I do have a timing light and vacuum gauge that I utilized to set my timing to factory specs. Tuning the carb has had no effect on settling the sporratic idling issue or the fact that it is running rich. It helps a little with the rich issue but not enough.

I tried searching but I'm stuck in my phone at the moment due to my computer being on the fritz and the search function isn't nearly as good via tapatalk as it is through the site itself nor does the site itself work quite right on my phone.

 

[blubuckaroo]

Check to see that the throttle stop screw is actually coming in contact with the throttle. I've seen the throttle linkage bind and hold the throttle open. Other than that, I'd keep looking for a vacuum leak. Is it using oil? I had one bad vacuum leak that was a split intake manifold gasket where the leak let two cylinders suck the oil out of the lifter galley. That was a hard one to trouble shoot.

 

[broncnaz]

Sporatic idle can be due to a still present vacuum leak that was missed or just is inttermitant. You could also have issues with the choke not opening correctly or not adjusted correctly. Which may be your issue with the high idle problems.

 

[DuctTape]

I was chasing vacuum leaks with a can of carb cleaner spraying it around the intake until I got them all sealed up. Fuel delivery is a known good. New pump, tank, lines, and filter. Plugs and wires are brand new as well as the distributor cap, coil, rotor, and ignition module. The only thing that I haven't changed is the vacuum advance on it. I do have a timing light and vacuum gauge that I utilized to set my timing to factory specs. Tuning the carb has had no effect on settling the sporratic idling issue or the fact that it is running rich. It helps a little with the rich issue but not enough.

I tried searching but I'm stuck in my phone at the moment due to my computer being on the fritz and the search function isn't nearly as good via tapatalk as it is through the site itself nor does the site itself work quite right on my phone.

I chased weird issues for a few months. Checked everything, tuned and re-tuned. Turned out to be a bad ignition module. It probably went bad because I left the ignition on while chasing an electrical problem. But the symptoms were weird. Maybe try a new ignition module? I hate to throw parts at a problem but sounds like you've gone thru the usual suspects so maybe it is the module?

It sucks as you apparently can't bench test a module, and it can be faulty without failing.

 

[rhino2104]

The killer about it is that it is a new ignition module. I have pictures of the old one. Nasty would be an understatement.

 

[jckkys]

The '76 2150 carbs have a vacuum operated choke pull off that will open the choke plate soon after the engine is started. Even if the pull off is working, the fast idle only comes off by it's own weight so even a little gunk can keep it from coming off consistently. A spray of carb cleaner should free that up. The carb originally had an idle stop solenoid that sets the curb idle when activated. If yours still has the solenoid use that to set the idle speed. A bad connection on this circuit could cause your symptoms.

 

[rhino2104]

Update on this for others with similar issues.

I got all of my issues straightened out. No more rich and no more rough, crappy idle or loading up. There weren't any vacuum leaks, all the seals were good, and no intake gasket leaks. It all boiled down to a bad float and needing a good cleaning and rebuild. Nearest I can tell the nitro float just got saturated over the years and wasn't causing the needle valve to seal off right so fuel was just being poured into it like mad.

Cliff notes: bad idle and running rich. Solution, good carb cleaning/rebuild and replace the bad float.