Spark plug readings.. having a tough time
Thread Starter
Racer
Joined: Dec 2009
Posts: 380
Likes: 0
From: Glendale AZ
Spark plug readings.. having a tough time
I'm having a few troubles with my 78 with a 350/290 GMPP Engine in it ...
The car had sat for some years so I had to overhaul the carb which is an edelbrock 1406 with what Im guessing are the stock jets.
Well anyway I'm experiencing surging at very light throttle and exhaust manifolds that are so hot they are melting anything within 6 inches of them so I'm assuming exhaust temp is hotter than it should be.
I pulled out the plugs and every single one of them are very white insulators with a large black spot on the side where the electrode is open. I know white is hot and black is rich but what do I do with both appearing at the same time?
I was going to go 1 stage richer on the metering rods to deal with light throttle surging but the plugs are making me think twice.. any ideas?
The car had sat for some years so I had to overhaul the carb which is an edelbrock 1406 with what Im guessing are the stock jets.
Well anyway I'm experiencing surging at very light throttle and exhaust manifolds that are so hot they are melting anything within 6 inches of them so I'm assuming exhaust temp is hotter than it should be.
I pulled out the plugs and every single one of them are very white insulators with a large black spot on the side where the electrode is open. I know white is hot and black is rich but what do I do with both appearing at the same time?
I was going to go 1 stage richer on the metering rods to deal with light throttle surging but the plugs are making me think twice.. any ideas?
Le Mans Master
Joined: Nov 2008
Posts: 5,691
Likes: 12
From: columbus oh
I'm having a few troubles with my 78 with a 350/290 GMPP Engine in it ...
The car had sat for some years so I had to overhaul the carb which is an edelbrock 1406 with what Im guessing are the stock jets.
Well anyway I'm experiencing surging at very light throttle and exhaust manifolds that are so hot they are melting anything within 6 inches of them so I'm assuming exhaust temp is hotter than it should be.
I pulled out the plugs and every single one of them are very white insulators with a large black spot on the side where the electrode is open. I know white is hot and black is rich but what do I do with both appearing at the same time?
I was going to go 1 stage richer on the metering rods to deal with light throttle surging but the plugs are making me think twice.. any ideas?
The car had sat for some years so I had to overhaul the carb which is an edelbrock 1406 with what Im guessing are the stock jets.
Well anyway I'm experiencing surging at very light throttle and exhaust manifolds that are so hot they are melting anything within 6 inches of them so I'm assuming exhaust temp is hotter than it should be.
I pulled out the plugs and every single one of them are very white insulators with a large black spot on the side where the electrode is open. I know white is hot and black is rich but what do I do with both appearing at the same time?
I was going to go 1 stage richer on the metering rods to deal with light throttle surging but the plugs are making me think twice.. any ideas?
Thread Starter
Racer
Joined: Dec 2009
Posts: 380
Likes: 0
From: Glendale AZ
Is there any kind of cheater method for checking my total timing? the indicator on the block only goes to +10 and i have a cheap non-adjustable gun
I set it at 10 degrees at 800 RPM.. assuming my tach is accurate
I set it at 10 degrees at 800 RPM.. assuming my tach is accurate
Last edited by volition; Dec 1, 2009 at 07:23 PM.
Thread Starter
Racer
Joined: Dec 2009
Posts: 380
Likes: 0
From: Glendale AZ
Burning Brakes
Joined: Nov 2005
Posts: 1,137
Likes: 51
From: Cartersville GA
After rebuilding my 1406 a few years back, I had been told that if it was surging at 1500 RPM (+/-) that the carb was too lean. I readjusted the idle screws and idle, and solved the surging problem. The color you discribe sounds like it's running lean.
There are threads here describing the proper method for setting the timing, and it works very well. I have the instructions in hard copy, but you should be able to do a search on timing, I believe Lars was the OP.
What condition are your mufflers in? I'm wondering if the car has been sitting and something nested in them which may have blocked them up. I've heard of this happening before, and resulting in very hot exhaust pipes/manifolds and poor operation. Just a thought.
There are threads here describing the proper method for setting the timing, and it works very well. I have the instructions in hard copy, but you should be able to do a search on timing, I believe Lars was the OP.
What condition are your mufflers in? I'm wondering if the car has been sitting and something nested in them which may have blocked them up. I've heard of this happening before, and resulting in very hot exhaust pipes/manifolds and poor operation. Just a thought.
Thread Starter
Racer
Joined: Dec 2009
Posts: 380
Likes: 0
From: Glendale AZ
Exhaust is all new duals with new cats. It smells like a lawnmower would be my best description. Before the exhaust was replaced it was leaking that exhaust smell that burned your eyes pretty bad.
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Drifting
Joined: Apr 2006
Posts: 1,911
Likes: 2
From: gold coast queensland
what is your engine temp? ....i wouldn't be concerned with how hot your exhaust gets, its your engine running temp thats the most important.
now lets get to what midyear said.... the cheater method is buying 5 dollar timing tape. wrap that sucker around your balancer and your standard timing lite will work just fine. you can then adjust base timing and mechanical advance timing with ease.
just a few questions....
-if it sat for years did you drain out all the old gas from tank?
-what are your settings on the edelbrock atm?
- are you sure there are no vacum leaks ?
this is probably the simplest timing video i have come across but i think if you have a true TDC and your on 10 at idle you cant be too far wrong....unless of course like midyear said...your getting none or too much mechanical advance.
http://www.setyourtiming.com/video.html
i probably wouldnt drive it till you can possibly try/burrow another carb to verify if it is in fact the culprit. if its that lean that your exhaust is an inferno and your plugs are white its BANG RATTLE BANG BANG TIME if you persist.
now lets get to what midyear said.... the cheater method is buying 5 dollar timing tape. wrap that sucker around your balancer and your standard timing lite will work just fine. you can then adjust base timing and mechanical advance timing with ease.
just a few questions....
-if it sat for years did you drain out all the old gas from tank?
-what are your settings on the edelbrock atm?
- are you sure there are no vacum leaks ?
this is probably the simplest timing video i have come across but i think if you have a true TDC and your on 10 at idle you cant be too far wrong....unless of course like midyear said...your getting none or too much mechanical advance.
http://www.setyourtiming.com/video.html
i probably wouldnt drive it till you can possibly try/burrow another carb to verify if it is in fact the culprit. if its that lean that your exhaust is an inferno and your plugs are white its BANG RATTLE BANG BANG TIME if you persist.
Last edited by gingerbreadman1977; Dec 2, 2009 at 07:24 AM.
Safety Car
Joined: Aug 2000
Posts: 3,711
Likes: 43
From: San Antonio TX
The black spots (called peppering) on the insulator are a sign you are detonating. Do not drive this car until you richen up the fuel mixture and get the timing adjusted. Most of your tuning concerns will be in the mixture. It's always better to run a little rich than a little lean. On an engine with a fuel mixture "in the ballpark" you would normally tune the ignition first, then the carb. You, however, need to get the carb in the ballpark first.
Le Mans Master
Joined: May 2002
Posts: 5,086
Likes: 786
From: Lebanon Township New Jersey
An even cheaper way to "cheat" on total timing mark is to scale off 30 degrees from the timing tab and transfer that measurement onto the balancer starting at the existing line on the balancer. Make some new lines with a pencil at 30 and 35 degrees and check the total, with vac advance disconnected, of course.
Le Mans Master
Joined: Apr 2001
Posts: 5,941
Likes: 281
From: Was New Orleans but swam to Baton Rouge LA
Cruise-In IX Veteran
Racer
Joined: Aug 2005
Posts: 308
Likes: 0
From: Salem MA
I havent done this, but you can weld an oxygen sensor bung into the exhaust and wire up a gauge and the sensor to take power from the cigarette lighter. You can then run the wires through the passenger door sill.
this way you can measure A/f mix directly and take out the sensor when not needed so modern tech doesn't clutter dash space.
this way you can measure A/f mix directly and take out the sensor when not needed so modern tech doesn't clutter dash space.
Thread Starter
Racer
Joined: Dec 2009
Posts: 380
Likes: 0
From: Glendale AZ
I did buy it a new tank so its clean but I've only been running regular since the engine is only 8.5:1 I guess I can step it up to premium.
Carb settings I'm not all that sure of to be honest, the numbers on the jets and rods are unreadable. I've got the tuning kit on the way with the assortment.
I did go through the carb entirely about a month ago it's operation seems to be 100% (pump jets are squirting and im getting am mist of fuel from main venturis) I felt it was probably running way too lean I'm just not much of an expert on the plug reading idea yet.
I've tuned all my previous cars which were Japaneese imports the cheating way using a AEM Wideband O2 sensor.. never had to do it the old fashioned way like this so I'm learning
I suppose at some point I'll have a bung welded on to make my life easier.
Thread Starter
Racer
Joined: Dec 2009
Posts: 380
Likes: 0
From: Glendale AZ
The black spots (called peppering) on the insulator are a sign you are detonating. Do not drive this car until you richen up the fuel mixture and get the timing adjusted. Most of your tuning concerns will be in the mixture. It's always better to run a little rich than a little lean. On an engine with a fuel mixture "in the ballpark" you would normally tune the ignition first, then the carb. You, however, need to get the carb in the ballpark first.
Melting Slicks
Joined: Jul 2006
Posts: 2,291
Likes: 493
From: Salmon Arm, BC
Go to the performance parts store and buy a timing tape for the diameter of your harmonic balancer......$5. Clean off balancer with brake clean.....stick on timing tape.....spray with clear lacquer to help seal out oil.....set timing to 36 degrees @3000 RPM
Thread Starter
Racer
Joined: Dec 2009
Posts: 380
Likes: 0
From: Glendale AZ
Spot on I'll see if I can track one down
