Carbon fouling plugs
- Thread starter butch27
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If that is the next hotter plug, that will be good. Carbon and soot can build up because of the short runs in addition to engine not coming up to proper temp. 180* plus, choke not coming off or set too rich, improper idle jet mixture, jetting too rich, float level too high, burning oil, etc. Most of these are simple to check and fix, short of the burning oil. I do not know what a detuned carb is. The last 2 Edelbrock carbs I dealt with were rich out of the box. Edelbrock sells a tune kit for about $40. Good luck,
Screaming Metal
Active Member
As RR said! Be sure to tune your idle mixture to where you just start missing (going lean), you'll have a slight miss, then richen it up just to barely clean it up (Motor smooths out).
Alot of motors when you adjust the mixture, you can compensate a little on your timing. You shouldn't have to go past 2 steps in the heat ranges....
The best running motors have some heat in them, heat is horsepower. Thats why Alum. heads aren't the best all the time. They act as heat sinks. Tune a drag motor for best et's, then go into some round robin rounds, where your putting heat into those heads, you have to completely retune things.
If you know how, find a old country road, and 'read' your plugs, if at all possible....
Alot of motors when you adjust the mixture, you can compensate a little on your timing. You shouldn't have to go past 2 steps in the heat ranges....
The best running motors have some heat in them, heat is horsepower. Thats why Alum. heads aren't the best all the time. They act as heat sinks. Tune a drag motor for best et's, then go into some round robin rounds, where your putting heat into those heads, you have to completely retune things.
If you know how, find a old country road, and 'read' your plugs, if at all possible....
21Scott
New Member
From your description, I would say your to rich. You can go one jet size down, and set the mixture screws. run your engine to full operating temp, then lower the idle so that any turn of the mix screws will be noticed. turn in until engine almost stalls, and turn out 1/8 turn each until it smooths out. go one 1/4 turn out more each. Remember in is rich, out is lean. I would stick to your manufacture plug #. If you are unable to lean it, you can drill 1/8" holes in the primary's. Scott
2old2fast
Active Member
Oh crap , here we go again .. DO NOT drill holes.... anywhere... in or out is not rich or lean ... unless it's one of the reverse flow holley's [ and there isn't many of those around] when you open the screw you're letting in more of the pre-determined air/fuel mix , the reverse is true when you close the screws , in order to richen/lean the mixture [ at idle is what we're talking about ] you either have to change the idle air bleeds or the idle jets . neither is generally advisable unless you are very experienced & have access to special tools..... this doesn't always apply to radical race stuff ,but that's another story..
dave
dave
Wild Mango
Member
Only reason you might drill the primary butterflies is if you running a decent cam and there is no manifold vacuum to speak of. That 302 is a stocker so should have plenty suckuum. Never seen butterflies drilled in an Edelbrock carb anyway. I would check the bowl levels, if they are around the top of spec I would take them down to bottom of spec. Put in a Tstat at the top of the heat range, set the idle on the lean side of OK, as Screamin' says. Maybe the little feller is loading up, and would benefit from a good blast on occasion to clear the coke out - good excuse, anyway.
I'm interested in what you mean by "detuned" as well.
I'm interested in what you mean by "detuned" as well.
Screaming Metal
Active Member
As the Mango said....you should have plenty of Vaccum unless you didn't give us all the info needed. Nowadays with all these new carbs, theres very little reason to drill those holes unless your running over .800 lift., thats not street territory there. Up. down, in or out, just thin out the idle mix. after putting a 180-190 in. I'm with Mango, its a damn hotrod, it don't even have fenders, hang your foot off into it every once in a while.
As 2O2F said....keep the ole power tools away from the carbs. The only people that should be allowed to drill holes in the front primarys are the ones THAT have changes the butterflys out before.....
As 2O2F said....keep the ole power tools away from the carbs. The only people that should be allowed to drill holes in the front primarys are the ones THAT have changes the butterflys out before.....
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Screaming Metal
Active Member
Let me also add, just putting around town, idling, not going out on the highway....your probably just running off your idle and transition circuits. Dribbling fuel can be a symptom of haveing a accelerator pump too tight. Or possibly a loose squirter nozzle. Hook up a vaccum gauge and see what you got.
Make sure you change that thermo to a 180-190, then put in the 1 step hotter plugs. Make sure everything is tight on your carb, that you level is on the bottom side of the sight hole. Take her for a spin, rev her up some.
If your plugs are really fluffy black, its running WAY rich. If its just a tad satin black its just a tad too much. If its a shiney black, its oil....unless you have fuel just pouring in....
Also, check and make sure your spark is plenty hot enough, good, clean plugs, full voltage to your ign. system, etc.
Did this just start happening all of a sudden or has it been a issue for a while?
Make sure you change that thermo to a 180-190, then put in the 1 step hotter plugs. Make sure everything is tight on your carb, that you level is on the bottom side of the sight hole. Take her for a spin, rev her up some.
If your plugs are really fluffy black, its running WAY rich. If its just a tad satin black its just a tad too much. If its a shiney black, its oil....unless you have fuel just pouring in....
Also, check and make sure your spark is plenty hot enough, good, clean plugs, full voltage to your ign. system, etc.
Did this just start happening all of a sudden or has it been a issue for a while?
Bump your timing up to 10* BTDC. If you are running 91 or 93, go up to 12* If you experience any valve rattle, hard starting or high engine temps, just start backing it down 1* at a time. If you are running one of the late model roller engines out of a Mustang you might be able to put in more timing. What dist are you running, vac adv, total timing, all in by what rpm. There is a lot of pep, power and drivability in optimum timing. Let me know which 302 you have and I might be able to throw some pointers out, if you want to try them.
I would go ahead and bump the timing up to 10*, make sure your vacuum advance is working. I usually just pull the dist cap, suck on the end of the line and watch to make sure the points plate moves and holds vacuum. Being a '69 dist, it could have a decent advance, but can definitely be improved if you have an adjustable timing light.
Not bashing your setup, but the 69, 70 heads are about the only stock heads that worth changing for a bolt on swap. Before everyone gets their shorts in a wad, that statement excludes the GT40 variations and 289 hp.
If your engine runs good, we will just concentrate on the issue and try to pep it up along the way.
Next, research the Pertronix electronic conversion with a new coil. You will get a hotter spark, better timing, less maintenance and probably less than $150. Summit Racing has a tech line, if you want to verify your decision on which model and coil to go with. This is a bolt on change, very simple. You will need to recheck your timing.
Keep us informed, good luck.
Not bashing your setup, but the 69, 70 heads are about the only stock heads that worth changing for a bolt on swap. Before everyone gets their shorts in a wad, that statement excludes the GT40 variations and 289 hp.
If your engine runs good, we will just concentrate on the issue and try to pep it up along the way.
Next, research the Pertronix electronic conversion with a new coil. You will get a hotter spark, better timing, less maintenance and probably less than $150. Summit Racing has a tech line, if you want to verify your decision on which model and coil to go with. This is a bolt on change, very simple. You will need to recheck your timing.
Keep us informed, good luck.
Mike
Well-Known Member
OK, I think it is time to address what is an ongoing problem, moreso in this particular forum than in some of the others. It is a touchy issue and my biggest concern is that raising the issue is going to cause hard feelings. Believe it or not, I am not trying to wind anyone up, so try not to get too fussed over anything I might say, from this point forward.
When we get someone asking for help with an engine problem, it seems about half of the time, the requests come with a real lack of any useful details. The other half of the time, the person wanting help gets overwhelmed with a dozen responses, with most of them being contradictory and the other most of them being downright wrong. Another half of the time, the person wanting help doesn't want to take and follow instructions. And the last half of the time, that person will not report back with details on what he is seeing, as a result of the advice he has been given.
Yeah, yeah, I know, it is impossible to have four halves of anything, but I think you get my drift.
I've raised this issue before, but it seems it could bear repeating.
If you have an engine problem you cannot sort, I have to believe you have at least tried to diagnose the problem before coming here to ask for advice. If that is the case, howzabout sharing what you have already tried, along with the results you saw, to save the rest of us a bit of time. If you don't have any spark and you've already checked things like primary voltage, then tell us that. I don't know how many times I have seen people ask for help, but when the first 147 people pile in with suggestions, the person asking for help will say, "I've already checked that," and, "I've already tried that." So, if you are asking for help, tell us what you have tried and what you have learned.
Details, details, details, give us the details. When someone says their car won't start, I find I don't know where to start, when it comes to trying to help. Heck, I don't know, is there fuel in the tank? Is there a battery in the car? Is the battery actually hooked up with the battery cables? Have you actually inserted the key in the ignition? I find most cars refuse to start without a key. Remember, if your car won't start and you are right there, on the scene, and cannot make it run, it is a much bigger problem for those of us who are hundreds or thousands of miles away to diagnose what is happening.
Then we come down to the problem when everyone is trying to help. I like when people show a willingness to help, because that shows people are being community-minded. And that is what makes discussion forums tick, having community-minded members. But if you are going to try to help, take a moment to assess your ability to help. Are you really capable of helping someone diagnose a problem of this kind? Are you really capable of coming up with a solution to the problem, or are you just trying to be community-minded?
Whilst I am reluctant to single anyone out, here is a perfect example of how using a shotgun approach can really foul up the process. 21Scott is going to end up thinking I am picking on him, but I am merely using his responses as an example.
#1 - I hate to be a grammar Nazi, but nothing makes a post more difficult to read than one where people fail to use common rules of grammar. The first word of a sentence should always be capitalized and punctuation should always be used to indicate the end of a sentence. Typing a post in all lower-case only makes it harder for people to read, same as posting IN ALL UPPER-CASE LETTERS. I realize we all make mistakes (I can be one of the worst, as I am almost always in a hurry and never take enough time to proof-read what I have written), but if we all use some common sense when composing a post, it can really help out the people who will be reading it.
#2 - If anyone is going to try to adjust idle mixture screws without a vacuum gauge, the process 21Scott gives is not reliable. First of all, set the idle speed screw, to achieve the idle you want/need. Focusing on just one mixture screw, slowly turn it in, until you notice the idle dropping. Then, start backing the screw out until you notice the idle picking back up, but keep going until you notice it dropping again. Then, turn the screw back in, until you get the highest idle speed. Then, go back to your idle speed screw and set the idle back to the number you want/need. Now, use the same process with the other screw, adjusting it for the highest possible idle speed. Then, go back to your idle speed screw and adjust it to get back to your target idle number. Now, go back to the first screw and start all over, following the exact, same procedure as before. You will notice the adjustment range will have narrowed, this time around. Just keep working, from idle speed screw to idle mixture screw, back to the idle speed screw, then over to the other idle mixture screw.
I prefer to use a vacuum gauge, setting all three of those idle screws for the highest, possible vacuum level. Then, there is no question it is right.
This business of an 1/8th of a turn here and then a 1/4 turn for good measure will not work the same, from vehicle to vehicle, because there are so many variables that come into play. Engine size, camshaft design, intake manifold design, ignition timing, and if you are really close with all of those, then even exhaust design can start having some effect. A 1/4 turn on a mixture screw might get a closely-tuned idle circuit completely out in left field, so don't fall into the trap. There will always be the one guy who has no clue what he is doing, but someone told him to add that extra 1/4 turn, so he figures if a 1/4 turn is good, then 3/8's of a turn will be just that much better.
When you are seeing carbon fouled plugs, you need to think your way through everything. Is fuel pressure acceptable, and not standing the needle off the seat? Is the float level set correctly? Is the choke opening properly? If it is a Holley, is the power valve blown? If you are certain the power valve is OK, is it opening at a level that is not introducing fuel before it is needed? Are idle mixture screws set properly? Are the main jets correct for the conditions? Is the accelerator pump nozzle properly sized and is the pump properly timed? My point being is that an improperly set choke can carbon foul a plug. A improperly adjusted float can carbon foul a plug. A blown or improperly-selected power valve can carbon foul a plug. Excessive fuel pressure can carbon foul a plug. Look at that, we've not gone anywhere near the idle mixture screws, the main jets, or Heaven forbid, the throttle blades. Nor have we considered that a dirty and damp distributor cap can carbon foul a plug, as can an oxidized distributor cap terminal, or an oxidized rotor tip, or a bad plug wire.
If you have an engine problem, use the most important tool you will ever own - that gray matter between your ears. Think about the problem and then think about all of the things that could be causing the problem. Don't run off to the parts store with a shopping list, because you still have not identified what is wrong. How can you ever hope to fix a problem, when you cannot even identify the problem?!? Start looking and testing, until you sort out what is wrong, then you only have to address the one issue. And if the problem is something as simple as a float level set too high, then there is no need to dash out and buy anything.
And last, but not least, let me remind everyone the information published in this Web site may be outdated or wrong in one way or another, and should not be used without independent verification or consultation with a professional. I always recommend everyone take any advice they get here with a grain of salt. You might even want to add a slice of lime and a shot of tequila.
When we get someone asking for help with an engine problem, it seems about half of the time, the requests come with a real lack of any useful details. The other half of the time, the person wanting help gets overwhelmed with a dozen responses, with most of them being contradictory and the other most of them being downright wrong. Another half of the time, the person wanting help doesn't want to take and follow instructions. And the last half of the time, that person will not report back with details on what he is seeing, as a result of the advice he has been given.
Yeah, yeah, I know, it is impossible to have four halves of anything, but I think you get my drift.
I've raised this issue before, but it seems it could bear repeating.
If you have an engine problem you cannot sort, I have to believe you have at least tried to diagnose the problem before coming here to ask for advice. If that is the case, howzabout sharing what you have already tried, along with the results you saw, to save the rest of us a bit of time. If you don't have any spark and you've already checked things like primary voltage, then tell us that. I don't know how many times I have seen people ask for help, but when the first 147 people pile in with suggestions, the person asking for help will say, "I've already checked that," and, "I've already tried that." So, if you are asking for help, tell us what you have tried and what you have learned.
Details, details, details, give us the details. When someone says their car won't start, I find I don't know where to start, when it comes to trying to help. Heck, I don't know, is there fuel in the tank? Is there a battery in the car? Is the battery actually hooked up with the battery cables? Have you actually inserted the key in the ignition? I find most cars refuse to start without a key. Remember, if your car won't start and you are right there, on the scene, and cannot make it run, it is a much bigger problem for those of us who are hundreds or thousands of miles away to diagnose what is happening.
Then we come down to the problem when everyone is trying to help. I like when people show a willingness to help, because that shows people are being community-minded. And that is what makes discussion forums tick, having community-minded members. But if you are going to try to help, take a moment to assess your ability to help. Are you really capable of helping someone diagnose a problem of this kind? Are you really capable of coming up with a solution to the problem, or are you just trying to be community-minded?
Whilst I am reluctant to single anyone out, here is a perfect example of how using a shotgun approach can really foul up the process. 21Scott is going to end up thinking I am picking on him, but I am merely using his responses as an example.
21Scott, that is something that is pretty obvious to everyone. If a plug is carbon-fouling, that particular cylinder is likely seeing more fuel than it is capable of burning. But this isn't really diagnosing the problem, because we do not know if the cylinder is seeing too much fuel, or if the ignition system is coming up lame.
At first blush, this seems to make good sense, but then we realize you are talking about two, completely different carb circuits, one being the idle circuit, the other being the main circuit. And, from the data in the original post, how can you possibly rule out even a third possible circuit, that being the choke system? Butch says he does a lot of short hauls, so this problem could be something as simple as a choke that is not opening up.
I see a couple of issues in the above.
#1 - I hate to be a grammar Nazi, but nothing makes a post more difficult to read than one where people fail to use common rules of grammar. The first word of a sentence should always be capitalized and punctuation should always be used to indicate the end of a sentence. Typing a post in all lower-case only makes it harder for people to read, same as posting IN ALL UPPER-CASE LETTERS. I realize we all make mistakes (I can be one of the worst, as I am almost always in a hurry and never take enough time to proof-read what I have written), but if we all use some common sense when composing a post, it can really help out the people who will be reading it.
#2 - If anyone is going to try to adjust idle mixture screws without a vacuum gauge, the process 21Scott gives is not reliable. First of all, set the idle speed screw, to achieve the idle you want/need. Focusing on just one mixture screw, slowly turn it in, until you notice the idle dropping. Then, start backing the screw out until you notice the idle picking back up, but keep going until you notice it dropping again. Then, turn the screw back in, until you get the highest idle speed. Then, go back to your idle speed screw and set the idle back to the number you want/need. Now, use the same process with the other screw, adjusting it for the highest possible idle speed. Then, go back to your idle speed screw and adjust it to get back to your target idle number. Now, go back to the first screw and start all over, following the exact, same procedure as before. You will notice the adjustment range will have narrowed, this time around. Just keep working, from idle speed screw to idle mixture screw, back to the idle speed screw, then over to the other idle mixture screw.
I prefer to use a vacuum gauge, setting all three of those idle screws for the highest, possible vacuum level. Then, there is no question it is right.
This business of an 1/8th of a turn here and then a 1/4 turn for good measure will not work the same, from vehicle to vehicle, because there are so many variables that come into play. Engine size, camshaft design, intake manifold design, ignition timing, and if you are really close with all of those, then even exhaust design can start having some effect. A 1/4 turn on a mixture screw might get a closely-tuned idle circuit completely out in left field, so don't fall into the trap. There will always be the one guy who has no clue what he is doing, but someone told him to add that extra 1/4 turn, so he figures if a 1/4 turn is good, then 3/8's of a turn will be just that much better.
As someone has already pointed out, that is simply not correct in most cases. IF the carb has a reverse idle circuit, then you are correct. However, if the carb has a standard idle circuit, then you are wrong. On nearly every carburetor ever built, the idle mixture screw needle is simply an obstruction to the amount of air-fuel emulsion passing through the idle circuit. Screw the needle in and you are cutting down the amount of emulsion moving through that passage. Back the needle out and more emulsion can flow.
No, no, no, no, no! Do not ever start indiscriminately drilling holes in throttle blades, particularly not in something that is being driven on the street. If you have a carb set for a race motor, you might not be able to take enough idle fuel away from it, which means drilling the throttle blades might be your only option. But the odds of ever having a street carb set up so rich are almost nil. Remember, once you start drilling throttle blades, you will want to be sure you have a ready supply of them, because they cannot be un-drilled. And yes, I have used pop rivets as an emergency fix at the race track, to plug up holes people have drilled in throttle blades.
When you are seeing carbon fouled plugs, you need to think your way through everything. Is fuel pressure acceptable, and not standing the needle off the seat? Is the float level set correctly? Is the choke opening properly? If it is a Holley, is the power valve blown? If you are certain the power valve is OK, is it opening at a level that is not introducing fuel before it is needed? Are idle mixture screws set properly? Are the main jets correct for the conditions? Is the accelerator pump nozzle properly sized and is the pump properly timed? My point being is that an improperly set choke can carbon foul a plug. A improperly adjusted float can carbon foul a plug. A blown or improperly-selected power valve can carbon foul a plug. Excessive fuel pressure can carbon foul a plug. Look at that, we've not gone anywhere near the idle mixture screws, the main jets, or Heaven forbid, the throttle blades. Nor have we considered that a dirty and damp distributor cap can carbon foul a plug, as can an oxidized distributor cap terminal, or an oxidized rotor tip, or a bad plug wire.
And to show I really am not trying to pick on you, let me say that I have no question you are correct in saying this. But when we start assuming apples are oranges, or vice-versa, then we are only assuming. Assuming is not a good diagnosis procedure and it makes for even worse tuning. And to think that the idle mixture settings for your own vehicle would be the same for everything? That just isn't how things work.
If you have an engine problem, use the most important tool you will ever own - that gray matter between your ears. Think about the problem and then think about all of the things that could be causing the problem. Don't run off to the parts store with a shopping list, because you still have not identified what is wrong. How can you ever hope to fix a problem, when you cannot even identify the problem?!? Start looking and testing, until you sort out what is wrong, then you only have to address the one issue. And if the problem is something as simple as a float level set too high, then there is no need to dash out and buy anything.
And last, but not least, let me remind everyone the information published in this Web site may be outdated or wrong in one way or another, and should not be used without independent verification or consultation with a professional. I always recommend everyone take any advice they get here with a grain of salt. You might even want to add a slice of lime and a shot of tequila.
Screaming Metal
Active Member
Its best for us old timers if you give us too much information than not enough. I deal with motors. Period. Anything and everything involved with motors. From a blown mountain motor at the track to a twin turbo setup, I've seen a human hair inside a mag stop a AA/FC from running down the track at a top meet.
It is all in the details given....if we are to diagnose a problem, we must 1st know exactly what its doing.
It is all in the details given....if we are to diagnose a problem, we must 1st know exactly what its doing.
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TriodeLuvr
Member
As noted above, it's difficult to diagnose fouled plugs from a distance. Enough ideas have been thrown out that it probably doesn't make sense to add more at this time. However, I think the issue of the carburetor idle screws needs clarification. The OP didn't mention the specific model, but the Edelbrock 1406 manual describes this function as follows:
"The Idle Screw Port is a variable discharge restriction that is adjusted by the engine tuner to achieve the desired A/F Ratio at engine idle."
An examination of the Edelbrock idle circuit agrees with this. It's true that the idle ports are fed with a pre-determined air/fuel mix, but the mix is not simply drawn into the manifold as-is. It is mixed with air passing through the transfer slot. Thus, as the amount of pre-determined mix is changed by turning the screws, the total A/F ratio is also changed. For this reason, I see no problem in referring to the idle screws as making the idle rich or lean.
My interpretation of the Edelbrock schematic is that turning the screws in causes the mixture to go lean, not rich as previously stated. Maybe someone can confirm.
Jack
"The Idle Screw Port is a variable discharge restriction that is adjusted by the engine tuner to achieve the desired A/F Ratio at engine idle."
An examination of the Edelbrock idle circuit agrees with this. It's true that the idle ports are fed with a pre-determined air/fuel mix, but the mix is not simply drawn into the manifold as-is. It is mixed with air passing through the transfer slot. Thus, as the amount of pre-determined mix is changed by turning the screws, the total A/F ratio is also changed. For this reason, I see no problem in referring to the idle screws as making the idle rich or lean.
My interpretation of the Edelbrock schematic is that turning the screws in causes the mixture to go lean, not rich as previously stated. Maybe someone can confirm.
Jack
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