Spark Plug Advice Needed

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bobscuda67

bobscuda67

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I am having a carbon problem on my intake and exhaust valves that I cleaned up last winter. It was quite thick on the intake and the exhaust indicating it was running very rich for years.
It's all back together now and I'm trying to get it to burn cleaner.
It's a 9.9:1 340 with magnum heads and a 650 Eddy Thunder carb stock calibration. The distributer is set at 34 degrees at 3400. Initial comes in at 16 degrees. The vacuum can is hooked to manifold vacuum. Exhaust manifolds are on it too. Cam is 220/226 Lunati. I use 87 octane with no spark knock.
The pictures to me say the timing is ok but the heat range is too cold. It's runs rich on the cruise and acceleration.
I ordered a set of rods for the carb that are 8% leaner on the cruise and accel. And I'm thinking two numbers on the plugs? Or is that too much of a jump?
The car runs good and the exhaust doesn't smell overly rich.
Just wondering if my thinking is a step in the right direction or if I'm reading it wrong.
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Lets get something clear for me. You say 16 initial and 34 all in by 3400. Then you say the vacuum can is on manifold vacuum. Now, did you set those timing figures with the vacuum hose disconnected? If not, that initial timing figure is very low, because "most" vacuum cans pull in about 20 degrees. Lastly, where is your vacuum can adjusted? You should "start" with it adjusted all the way clockwise, as that allows the maximum advance to be pulled in with the minimum vacuum setting. Then if you get spark knock, turn it counter clockwise until it stops. BUt if no spark knock all the way clockwise, then leave it be.
 
My suggestion would be to start with the basics. A good tune up, making sure the timing is correct and getting the carburetor lined out with a vacuum gauge. Don't inspect the plugs after puttering around the neighborhood, take it out for a highway run and then inspect the plugs at the first available wide spot in the road.
 
Doesn't manifold vacuum drop off as engine speed increases? If this is true then why hook up the vacuum advance to manifold source. If the vacuum drops off as engine speed increases then your vacuum advance isn't even working. If it was me I would do a complete tune up including tuning the carb
 
Dan the man said:
Doesn't manifold vacuum drop off as engine speed increases? If this is true then why hook up the vacuum advance to manifold source. If the vacuum drops off as engine speed increases then your vacuum advance isn't even working. If it was me I would do a complete tune up including tuning the carb
Click to expand...

When vacuum drops the load goes up. More load needs less timing. Unless it absolutely positively had to have it hook to manifold vacuum I’d hook it to ported vacuum.
 
Im seeing very rich. It's hard to tell in the picture but it appears to want more initial timing if I'm seeing it right. And yes it is cold
 
Yes, NGK 5 heat range would be best. Using Manifold connected Vacuum Advance [ MVA ]. A reallllllllly good idea with that cam.

But you have to get it [ idling timing ] right first. You adjust the carb last.

This is how you do it. Disconnect & plug the VA. Engine idling, in gear if auto, starting with the dist giving about 10-12* at idle. Turn the dist slowly to advance timing until you have the highest idle speed. Now check the timing. My guess is it will be in the 20-35* range. Whatever it is, it is what THAT engine needs.

So let us say you got 26*. You can use any combination of init + MVA to give 26*. If you were using 12* before, you can add 14* with the VA unit. You will probably need to make a stop to limit total timing added by the VA arm. This is ALL part of tuning once you deviate from stock.
With this done, re-adjust carb idle setting. I doubt the met rods will need changing once timing is correct because running with insufficient timing makes the engine inefficient & it uses more fuel to cover the inefficiency.

Things to note:
- you need an adj VA unit. None of the above will work with a stock unit. Even if you have to buy a new dist....
- adjust Allen screw in the VA fully CW.
- see below on idle timing
- the carboned up valves is from oil leakage past the valve guides, NOT richness.

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Dan the man said:
Doesn't manifold vacuum drop off as engine speed increases? If this is true then why hook up the vacuum advance to manifold source. If the vacuum drops off as engine speed increases then your vacuum advance isn't even working. If it was me I would do a complete tune up including tuning the carb
Click to expand...
More throttle opening means denser air fuel charge and therefore faster burn. So less timing is needed to take advantage of the combustion.
 
Thanks all for the coaching.
I had my distributer spun by Don at FBO and I just dug up the build sheet on it.
It says initial is at 16 degrees.
Vacuum timing can is 14 degrees at 14 inches of vacuum.
18 degrees at 3400.
I set the timing at 34 degrees at 3400 rpm with the vac advance plugged off and 16 degrees was the idle number it settled on.
And it's connected to manifold vacuum because it's so rich at idle it allows me to close the throttle at idle to close some of the transfer slot down. These 650 Edelbrocks are known to be rich at idle.
I hand lapped the valves and installed new valve stem seals on the heads last winter. Forgot to add that part.
Yes, these plugs have 100 miles on them puttering around. I'll change that on the next plug coloring trip.
Hope this clears up some of the confusion.
 
What your running is about identical to what my 340 is at. Let us know how you make out with the plugs.
 
bobscuda67 said:
Thanks all for the coaching.
I had my distributer spun by Don at FBO and I just dug up the build sheet on it.
It says initial is at 16 degrees.
Vacuum timing can is 14 degrees at 14 inches of vacuum.
18 degrees at 3400.
I set the timing at 34 degrees at 3400 rpm with the vac advance plugged off and 16 degrees was the idle number it settled on.
And it's connected to manifold vacuum because it's so rich at idle it allows me to close the throttle at idle to close some of the transfer slot down. These 650 Edelbrocks are known to be rich at idle.
I hand lapped the valves and installed new valve stem seals on the heads last winter. Forgot to add that part.
Yes, these plugs have 100 miles on them puttering around. I'll change that on the next plug coloring trip.
Hope this clears up some of the confusion.
Click to expand...

I’m confused. The carb is pig rich at idle so you hooked up manifold vacuum to fix that?

I guess my question is why not fix the carb?

Lots of carbs are rich at idle. Some aren’t rich but they are lean. They misfire and smell rich but they are really lean.

Either way, sorting out the carb and getting it right is far better than jacking a bunch of timing in it at idle.
 
Bewy said:
Yes, NGK 5 heat range would be best. Using Manifold connected Vacuum Advance [ MVA ]. A reallllllllly good idea with that cam.

But you have to get it [ idling timing ] right first. You adjust the carb last.

This is how you do it. Disconnect & plug the VA. Engine idling, in gear if auto, starting with the dist giving about 10-12* at idle. Turn the dist slowly to advance timing until you have the highest idle speed. Now check the timing. My guess is it will be in the 20-35* range. Whatever it is, it is what THAT engine needs.

So let us say you got 26*. You can use any combination of init + MVA to give 26*. If you were using 12* before, you can add 14* with the VA unit. You will probably need to make a stop to limit total timing added by the VA arm. This is ALL part of tuning once you deviate from stock.
With this done, re-adjust carb idle setting. I doubt the met rods will need changing once timing is correct because running with insufficient timing makes the engine inefficient & it uses more fuel to cover the inefficiency.

Things to note:
- you need an adj VA unit. None of the above will work with a stock unit. Even if you have to buy a new dist....
- adjust Allen screw in the VA fully CW.
- see below on idle timing
- the carboned up valves is from oil leakage past the valve guides, NOT richness.

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Click to expand...
Bewy: What book is this? I'd like to get me a copy. I found What you wrote very interesting and I would like to read more. Thanks for sharing this information. Have a good day
 
Ok, I copied to word document then pdf. I forget where I found the article.
 

Attachments

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Dan,
That book is David Vizard's How to Tune Holleys, CarTech SA216.
Ign timing in a Carb book? And ign timing mentioned several times?

That is because DV gets the relationship between idle timing & carb idle setting. Many do not get it......

Idle timing is done first before touching the carb. Quite often, problems such as off idle flat spots will be cured or reduced once the timing at idle is correct. The usual problem is not enough timing at idle, not too much.
For reasons known only to Chrys, they did not use man vac adv [ MVA ], instead used the useless PVA. GM used MVA. My 1966 showroom stock Pontiac idled @ 26*: 6* init + 20* MVA; with a very mild cam & 10.75:1. [ Chevs used about 24* ] With more cam & lower CR, vac is reduced & even more timing is needed.
'Lots of carbs are rich at idle'. Only if there is a manufacturing fault where the mixture screws do not seat against their seats.....& that would be rare. If the T slot position is correct, screwing in the mixture screws will stall or almost kill the engine from lack of fuel.
The idle fuel feed is sized to provide enough fuel for transition [ to the main cct ] NOT for idle which requires less fuel & is regulated by the mixture screws.
 
I put a timing light on it yesterday and at idle the engine is really happy at 35 degrees advanced and it has 20 inches of vacuum. I tried to check the advance at idle with the 16 initial and connected to manifold vacuum but the bulb burned out on my timing light.
I was told by FBO when they set my distributer to switch to manifold vacuum. It gives me more control over the mixture screws, and reduces transfer slot exposure to vacuum. I can kill the engine with the mixture screw.
I'm going to buy a couple spark plugs one heat range hotter and run the car on the expressway with a clean cut off and I'll cut those apart. That's going to have a lot of new information.
 
When I set the idle mixture screws I turned them all the way in until it stumbled then turned out 1/4 turn. That seemed to help more than using a vacuum gauge.
Cut another plug open today and it's a little bit rich.
If you look down the threaded shell you can see it's black all the way down.
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bobscuda67 said:
When I set the idle mixture screws I turned them all the way in until it stumbled then turned out 1/4 turn. That seemed to help more than using a vacuum gauge.
Cut another plug open today and it's a little bit rich.
If you look down the threaded shell you can see it's black all the way down.
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Click to expand...


That’s not a little rich. That’s very fat. These threads all run together after a while but aren’t these plugs out of an engine that is using manifold vacuum because the carb is fat?

If so, fix the carb BEFORE you start with timing. You are far enough off that it’s cause you to jack more timing in it than it needs.

Edit: I just went and looked and if you are sure you have 9.9:1 compression there is no way, no way it needs that much timing at idle with your cam.

Not even close.
 
When the engine was built the math did work out to a touch over 9:9 to 1.
Like I said before that Don spun the distributer and set all the advance and vac can for me.
I filled out a very long spec sheet that he sent me and he came up with the curve. And if you look at some of the first pictures I posted you can see the timing line just below the radius of the ground strap indicating the timing is really close to perfection for my engine.
I have some rods coming that will lean it out 8% at cruise and power mode. I'm going to try some hotter plugs too.
 
Newbomb Turk said:
That’s not a little rich. That’s very fat. These threads all run together after a while but aren’t these plugs out of an engine that is using manifold vacuum because the carb is fat?

If so, fix the carb BEFORE you start with timing. You are far enough off that it’s cause you to jack more timing in it than it needs.

Edit: I just went and looked and if you are sure you have 9.9:1 compression there is no way, no way it needs that much timing at idle with your cam.

Not even close.
Click to expand...
I totally agree with this. Nothing wrong with using manifold vacuum on the vacuum can if it runs better, BUT unless you fix the carburetor FIRST, you're just using manifold vacuum as a band aid.
 
remytherat said:
More throttle opening means denser air fuel charge and therefore faster burn. So less timing is needed to take advantage of the combustion.
Click to expand...
It feels a bit nit picky, but the density doesn’t change. The volume does.
 
Dan the man said:
Doesn't manifold vacuum drop off as engine speed increases? If this is true then why hook up the vacuum advance to manifold source. If the vacuum drops off as engine speed increases then your vacuum advance isn't even working. If it was me I would do a complete tune up including tuning the carb
Click to expand...
ported and mechanical track pretty much the same with the exception at closed throttle. there is no ported vacuum with the throttle blades closed.
 
RustyRatRod said:
I totally agree with this. Nothing wrong with using manifold vacuum on the vacuum can if it runs better, BUT unless you fix the carburetor FIRST, you're just using manifold vacuum as a band aid.
Click to expand...
Right. I have the rods for the carb coming that will lean it out. Just waiting for the mail.
It'll lean out 8% at cruise and power.
I just picked up one step hotter spark plug to try.
When the rods get here I'll take it on the expressway and get a clean shutoff and cut that plug apart. That will show if it's going in the right direction.
I really didn't want this thread to be another manifold vs ported vacuum discussion.
 
bobscuda67 said:
Right. I have the rods for the carb coming that will lean it out. Just waiting for the mail.
It'll lean out 8% at cruise and power.
I just picked up one step hotter spark plug to try.
When the rods get here I'll take it on the expressway and get a clean shutoff and cut that plug apart. That will show if it's going in the right direction.
I really didn't want this thread to be another manifold vs ported vacuum discussion.
Click to expand...
My bad. I'll shut it down on my end then. Don't forget about the pump shot on that carburetor. Lots of times, when you lean one out it will get a stumble off idle, because it may need more pump shot so keep that in mind.
 
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