Running Lean
Thread Starter
Advanced
Joined: Apr 2014
Posts: 66
Likes: 4
From: Alvin, Texas
Running Lean
When I changed out my plugs I mentioned to a friend that some of my plugs had a white film on them and were a bit fouled. He said sounded like the car was running a bit lean. How can you tell if the car is running lean? What would need to be done to correct this and how can you tell if all is good after making the correction? Thought I would throw this out to the group as I am still learning. Thanks in advance for any recomendations.
Melting Slicks
Joined: Dec 2009
Posts: 3,229
Likes: 656
From: Thunder Bay
3 ways come to mind. Reading the plugs is the traditional way of analyzing mixture. White is lean, black is rich, tan is what you are looking for. There's a lot more to it, but that's the Reader's Digest version.
There is also a device some mechanics use which samples the tailpipe gasses. I've never used one so I don't know a lot about it.
Nowadays the state of the art is to install an Air/Fuel mixture guage. This uses an oxygen sensor installed in the exhaust pipe to sample the exhaust gasses in real time so you can see your mixture as you drive. I put one in my '79 and it works great.
There is also a device some mechanics use which samples the tailpipe gasses. I've never used one so I don't know a lot about it.
Nowadays the state of the art is to install an Air/Fuel mixture guage. This uses an oxygen sensor installed in the exhaust pipe to sample the exhaust gasses in real time so you can see your mixture as you drive. I put one in my '79 and it works great.
Safety Car
Joined: Aug 2000
Posts: 3,711
Likes: 43
From: San Antonio TX
First, you need to Google "spark plug deposit pictures" and compare your plugs to get some idea if what you're seeing is normal or not. It sounds more like you have ash deposit, which comes from burning oil.
As to an engine running lean or rich; Those conditions cause performance issues. If an engine runs fine -and by "fine" I mean it starts easily, has a stable idle, exhibits no driveability issues and uses fuel efficiently- then it is not rich or lean. That's just the condition the engine likes regardless of what a meter might show.
An air/fuel ratio (AFR) meter might show your engine idles at 13.5:1 AFR. You lean it out to try to get to, or close to the magical 14.7:1 and the idle goes unstable, it's hard to start and keep running cold. The exhaust might stink as well from a lean misfire. So you now have an engine that runs poorly but looks good on the meter.
I understand, based upon your question, you don't have a AFR meter or the experience to make absolute determinations about your fuel system. This is just some advice to not start chasing your tail on a problem you may not have. Again, compare your plugs to the pictures and work slowly toward a diagnosis.
As to an engine running lean or rich; Those conditions cause performance issues. If an engine runs fine -and by "fine" I mean it starts easily, has a stable idle, exhibits no driveability issues and uses fuel efficiently- then it is not rich or lean. That's just the condition the engine likes regardless of what a meter might show.
An air/fuel ratio (AFR) meter might show your engine idles at 13.5:1 AFR. You lean it out to try to get to, or close to the magical 14.7:1 and the idle goes unstable, it's hard to start and keep running cold. The exhaust might stink as well from a lean misfire. So you now have an engine that runs poorly but looks good on the meter.
I understand, based upon your question, you don't have a AFR meter or the experience to make absolute determinations about your fuel system. This is just some advice to not start chasing your tail on a problem you may not have. Again, compare your plugs to the pictures and work slowly toward a diagnosis.
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,171
From: Hermosa
Here is a pretty good write up on plug reading.
http://4secondsflat.com/Spark_plug_reading.html
And here go to post #10. Lots of pics of plugs
http://www.jockeyjournal.com/forum/s...8674&showall=1
http://4secondsflat.com/Spark_plug_reading.html
And here go to post #10. Lots of pics of plugs
http://www.jockeyjournal.com/forum/s...8674&showall=1
Thread Starter
Advanced
Joined: Apr 2014
Posts: 66
Likes: 4
From: Alvin, Texas
First, you need to Google "spark plug deposit pictures" and compare your plugs to get some idea if what you're seeing is normal or not. It sounds more like you have ash deposit, which comes from burning oil.
As to an engine running lean or rich; Those conditions cause performance issues. If an engine runs fine -and by "fine" I mean it starts easily, has a stable idle, exhibits no driveability issues and uses fuel efficiently- then it is not rich or lean. That's just the condition the engine likes regardless of what a meter might show.
An air/fuel ratio (AFR) meter might show your engine idles at 13.5:1 AFR. You lean it out to try to get to, or close to the magical 14.7:1 and the idle goes unstable, it's hard to start and keep running cold. The exhaust might stink as well from a lean misfire. So you now have an engine that runs poorly but looks good on the meter.
I understand, based upon your question, you don't have a AFR meter or the experience to make absolute determinations about your fuel system. This is just some advice to not start chasing your tail on a problem you may not have. Again, compare your plugs to the pictures and work slowly toward a diagnosis.
As to an engine running lean or rich; Those conditions cause performance issues. If an engine runs fine -and by "fine" I mean it starts easily, has a stable idle, exhibits no driveability issues and uses fuel efficiently- then it is not rich or lean. That's just the condition the engine likes regardless of what a meter might show.
An air/fuel ratio (AFR) meter might show your engine idles at 13.5:1 AFR. You lean it out to try to get to, or close to the magical 14.7:1 and the idle goes unstable, it's hard to start and keep running cold. The exhaust might stink as well from a lean misfire. So you now have an engine that runs poorly but looks good on the meter.
I understand, based upon your question, you don't have a AFR meter or the experience to make absolute determinations about your fuel system. This is just some advice to not start chasing your tail on a problem you may not have. Again, compare your plugs to the pictures and work slowly toward a diagnosis.
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,171
From: Hermosa
Right now the car is a bit hard to start after sitting. I know she is pretty old but I believe some of it has to do with the fuel pump.
Seems to run pretty well but still a bit of hesitation off the start, at least until it gets up to 35 or 40mph.
The accelerator pump squirts fuel into the carb when you push the pedal down so that the engine has enough fuel for the initial pedal movement. It also helps in starting the engine when you pump the gas pedal.
Thread Starter
Advanced
Joined: Apr 2014
Posts: 66
Likes: 4
From: Alvin, Texas
Just a quick update out to all. Had the car looked at Saturday and after several tests and a lot of checking, it looks like a valve job is needed. Checked the carburator and it looks to be fine. No adjustments made a difference. When pulling the wires from the dist cap, no drop off when pulling #4 and #8. Number 4 valve is not sealing. Number 8 is acting the same way so we are thinging that one is not sealing as well. Since that one was difficult to get to we didn't do all the tests on it as we did on #4. Compression is good in all cylinders but when blowing air into the #4 cylinder can see fumes coming up from the carb, nothing coming from the exhaust. Number 4 plug slightly burned and has a bit of fuel on it. Plugs next to it looks brand new and no vacuum leaks. Looks like about $750 for the fix. Hope to have her running good soon. Appreciate all the help from you all, will keep everyone updated.
