Plug fouling on 79 308
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Plug fouling
DJ, I just finished replacing the plugs with NGK BPR5EVX plugs. These are a hotter plug and hopefully won't carbon out as quickly. They really have brought the performance back and it seems a little better. You are correct in that I should drive it more than I do. I choose not to drive it that much so I guess I'll just have to buy plugs more often. BRGDS, Magoo
DJ, I just finished replacing the plugs with NGK BPR5EVX plugs. These are a hotter plug and hopefully won't carbon out as quickly. They really have brought the performance back and it seems a little better. You are correct in that I should drive it more than I do. I choose not to drive it that much so I guess I'll just have to buy plugs more often. BRGDS, Magoo
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How has it been running since you've cleaned the jets? Is it still fouling after that?
Carbon build-up shows the condition in the combustion chambers at idle, just before you shut the car down. To find out if its fouling during higher RPM's, you must do a "plug-cut" and check it then (drive car on a clear, wide road. Drive at around ~4500 RPM and at the same time, turn off the ignition and put car into neutral. BE CAREFUL WHEN PULLING OVER TO THE SIDE OF THE ROAD, SINCE YOUR ENGINE IS OFF, YOU ARE NO LONGER GETTING VACUUM BOOST TO THE BRAKES, THE CAR WILL BE HARD TO STOP - THATS WHY YOU ARE DOING THIS ON A CLEAR WIDE ROAD WITH LITTLE TRAFFIC, JUST IN CASE SOMETHING DOESN'T GO RIGHT WHEN TRYING TO STOP...).
:wink:
Carbon build-up shows the condition in the combustion chambers at idle, just before you shut the car down. To find out if its fouling during higher RPM's, you must do a "plug-cut" and check it then (drive car on a clear, wide road. Drive at around ~4500 RPM and at the same time, turn off the ignition and put car into neutral. BE CAREFUL WHEN PULLING OVER TO THE SIDE OF THE ROAD, SINCE YOUR ENGINE IS OFF, YOU ARE NO LONGER GETTING VACUUM BOOST TO THE BRAKES, THE CAR WILL BE HARD TO STOP - THATS WHY YOU ARE DOING THIS ON A CLEAR WIDE ROAD WITH LITTLE TRAFFIC, JUST IN CASE SOMETHING DOESN'T GO RIGHT WHEN TRYING TO STOP...).
:wink:
plug fouling
I guess I am missing something here. After I turn the ignition off and come to a stop, then what? Another caution to those who may try this, Don't turn the ignition off to the" lock up" steering position. You may travel in circles for a while.
I guess I am missing something here. After I turn the ignition off and come to a stop, then what? Another caution to those who may try this, Don't turn the ignition off to the" lock up" steering position. You may travel in circles for a while.
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Ooops, sorry Magoo, I assumed you knew to remove the spark plugs from the engine, once you had completed the exercise (shut off, pull car over, remove plugs).
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575 Posts
(For some reason I couldn't post in this topic, or others in the last couple of days. But it looks like I can reply to your question Magoo).
The conditions in the combustion chamber change constantly during operation, this is due to the quantity of air/fuel mixtures, advance of the spark and load the engine is carrying. Our Webers (and FI as well) are delivering different amounts of fuel mixture because of throttle imputs, so if you were to "cut" the entire process at once (by shutting the engine off at speed), whatever mixture was combusting at that moment will deposit on the plugs. If you made any changes in the main circuit (air correctors, emulsion tubes, main jets), you'd be able to read the plugs and determine the condition (you'd also get a general idea by the way the car was running at those speeds, but thats by the seat-of-your-pants).
Now, if your plugs have 1XXXX's of mi on them, and you've been running the car too lean, or have other defects and the plugs are physically damaged (heat breaking off the insulator, build-ups, oil-fouling from old seals/rings), then you can't read them. New plugs would be recomended and then do a "plug-cut".
The conditions in the combustion chamber change constantly during operation, this is due to the quantity of air/fuel mixtures, advance of the spark and load the engine is carrying. Our Webers (and FI as well) are delivering different amounts of fuel mixture because of throttle imputs, so if you were to "cut" the entire process at once (by shutting the engine off at speed), whatever mixture was combusting at that moment will deposit on the plugs. If you made any changes in the main circuit (air correctors, emulsion tubes, main jets), you'd be able to read the plugs and determine the condition (you'd also get a general idea by the way the car was running at those speeds, but thats by the seat-of-your-pants).
Now, if your plugs have 1XXXX's of mi on them, and you've been running the car too lean, or have other defects and the plugs are physically damaged (heat breaking off the insulator, build-ups, oil-fouling from old seals/rings), then you can't read them. New plugs would be recomended and then do a "plug-cut".
Now that makes sense
Thanks Peter, I just installed new plugs and it seems to be running much better now. One thing I have learned is letting the car idle and taking a long time to trim out the carbs can foul up the plugs quickly. At least in my car. I may try what you said to check them out. Thanks for the "Tip." Magoo
Thanks Peter, I just installed new plugs and it seems to be running much better now. One thing I have learned is letting the car idle and taking a long time to trim out the carbs can foul up the plugs quickly. At least in my car. I may try what you said to check them out. Thanks for the "Tip." Magoo
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OK, OK, I'm no automobile mechanic, but maybe I can offer some help. I'm a private pilot (single-engine land, instrument pilot ratings). During ground operations, we start and run up the engine with mixture FULL RICH. A good pilot knows to lean out the mixture during taxiing and holding position short of the runway waiting for permission for take-off. The spark plugs tend to foul (and there are 2 spark plugs per cylinder) when the mixture is too rich. Leaning out the mixture burns off the carbon deposits and you can see this with a rise in RPM for a set throttle position. We go back to full rich for take-off. In this way, we are assured of an efficient engine during a critical stage of flight. We lean the mixture again at altitude to compensate for decreased air density.
A long story, I admit, but maybe the chronic fouling is due to too rich a mixture? Idling too long is certainly a factor. A carburettor adjustment could help. Or maybe the choke cable needs to be checked.
A long story, I admit, but maybe the chronic fouling is due to too rich a mixture? Idling too long is certainly a factor. A carburettor adjustment could help. Or maybe the choke cable needs to be checked.
Great example. The concept is really no different with turbine engines. When I was flying Blackhawks, we would always get better "gas mileage" at altitude (i.e. instruments, cross-country or maintenance test flights) than down in the weeds where the air was more dense; it didn't help with the fact that we were constantly yanking on the collective for changes in terrain, powerlines, "enemy air defense artillery," etc.
Even commuter airlines will climb as high as possible even for a short trip; good gas mileage=cost effectiveness=you get the can of pop instead of just the cup....
Forza,
Dane
Even commuter airlines will climb as high as possible even for a short trip; good gas mileage=cost effectiveness=you get the can of pop instead of just the cup....
Forza,
Dane
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