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eric32 04-10-2010 07:56 PM

Keep going through spark plugs, need some advice.
Hello guys well I am once again putting in a new set of spark plugs in my 350 small block chevy and am trying to figure out why I keep going through them. Engine is 350, World sportsman 2 heads, 9:1 compression or a hair more. Flat top pistons, Edelbrock rpm performer, Crane hydraulic roller cam 222/230 @ 50 112 lsa with 505/515 lift. Carburetor is a holley 600 1850s with 70 primary and 76 secondary jets. Transmission is a turbo 350 with a 2200 stall.

Engine holds about 12 inches of vacuum at idle. The carb has been tuned and it runs very well with excellent throttle response and idles at 800 in park. I just recently installed a manual choke and had to go through a couple of pulls with starting and shutting it off before I could get it correct to give me a 1500 rpm idle with the choke pulled at the right spot. After doing that my plugs fouled a little but after I took it out for a good drive they cleaned up and where not fuel fouled at that point.

Am running NGK 6630 plugs gaped at .045 as recommended per there specs. Everything is new from top to bottom and the timing is set perfect at 16 initial and all in by 3500 rpm. Running brand new HEI with plug wires as well. Had issues with a brand new holley street avenger last fall and finally got a nice holley 600 brand new to put on. Had everything set good with this motor and it seemed around January things got weird after I installed a one inch spacer. I had issues with the pcv valve sucking up oil so I took it off about a month ago and installed a breather for now and is vented on both valve covers.

Installed a new set of plugs about a month ago and noticed when I start it up in a cold morning I give it a couple of shots of gas then it fires right up and it seems like it will want to spit and sputter a little bit but nothing major. After its warmed up it runs excellent and fine with no rich running conditions or anything like that.

But I keep having a miss here and there and when it is idling it will seem to drop one cylinder and then come back on. All has been checked and I drive this truck about 12 miles round trip each day to work. About 3 miles in city and 3 highway. I let it warm up for about 5 minutes till temp gauge starts to go up then take off. New coil, cap, and rotor as well. Is my engine to much for a daily driver type deal with a little performance? Wondering if I have too much of a cam but it does not seem that big. Has a lope at idle but nothing rough.

Everything has all been checked and don't know what is causing my plugs to get fouled out over time. Pulled plugs today and they did not smell like gas but where dry but over time like I have posted else where before is clean on outer part but is always oil on the lower threads. Same thing happens on my other 350 as well but thats another story. This is on all eight cylinders and the engine is a fresh build from last summer and has about 2000 miles or a little more on it. Any suggestions on what to check and do? Motor had brake in period and motor was all blueprinted and built by myself and my dad who has built hundreds over the years.

Did a compression on the on cylinder the one time and had 160 psi at idle.

Thanks and sorry for long post.

automotive breath 04-10-2010 08:43 PM

It sounds like you have enough ignition advance at low RPM, have you tried

It could be tuned too rich at idle, have you tried leaning it out? Rich idle will
run real good but foul plugs, what you want is on the edge, almost too lean.

It shouldn't need a choke, it will kill the plugs in an instant. I haven't used
one in 30 years.

carsavvycook 04-10-2010 09:25 PM


Originally Posted by F-BIRD'88
Reinstall the PCV correctly , rejet the carb to 65-67 pri and 73-75 sec.
6.5" power valve.

Eliminating the pcv makes the idle circuit afr way too rich.
And makes the throttles too far open at idle. Too muich idle transfer slot exposure at idle.
Fix the valve cover baffling and PCV hole location so it does not suck up oil.
Most of the pretty aftermarket valve covers are designed wrong.
When you correct everything you fubared up the plugs will run clean.

It could not have been explained more correctly. :thumbup:

eric32 04-11-2010 07:44 AM

Well some great tips here guys thanks for all the info. Ok on my carburetor I did not use the stock jetting cause I figured it would be to lean with the 65 on the primary's. My Dad has the same carb on a stock 302 ford and it has the same primary jets. His motor has only about 225 hp as to where mine is pushing 400 so I know it would take more in fuel wise and thus would require a couple of size up in jet size correct? If I am wrong by all means fill me in :)

Now on the part of the pcv valve how does it affect the idle circuit on the carburetor by chance? That is the first I have heard that one and am trying to learn all the knowledge I can get. I never plan on racing this thing just having something nice to drive and run good and strong.

On my valve covers they are made for Jegs and they are stamped steel chrome ones. The baffles are in the right spot between two rocker arms. They actually have what seems like a good baffle system installed but they are welded and would not know what to do to make them better for not letting oil get up on top. They are also tall style valve covers.

I had already got the idle set as lean as I can get it. I cracked open the secondary's to allow more air flow at idle and the transfer slot is exposed only about .040 to.045 at the most and that was actually how holley had it when it came with the factory setting but I still had to adjust it but is still within the specs I said above. I have a holley tuning book from SA design and have read that thing back and forth using as much info as possible. The idle mixture screws are 1.5 turns out. If I go to one turn out the engine gets to rough and if you turn it back in more and have less then one turn out say about 3/4 the motor dies so the idle mixture has to be as lean as possible but other then that.

I only put my choke on for winter use I just had to get it set and such. But using the choke is it not basically the same thing as holding your gas pedal down to get your idle up to 1500 rpm anyways? I wanted to use it so my truck can warm up during winter while I can go back inside my house if I have to do a few things. Was told the choke flap helps create a suction vacuum affect and actually helps your engine warm up better that way then just holding the gas pedal down. Ok fbird how do I get a dummy pcv valve? Do I just take the guts out of one? I do thank you guys for your help. Will try some of the suggestions.

red65mustang 04-11-2010 09:19 AM

your motor and cam combo should be able to show 14-15Hg at idle at 800-900 rpms warmed up tuned correct...
(which is plenty good)

on the street a carb want/needs about/atleast 13Hg at idle to make a decent "atomized" spray that will stay in suspension with the air all the way into the cylinders so it will burn with such slow piston speed...

ex/illustration based on your first post:
(liquid gas does not burn)
with the present only 12Hg worth of atomization quality and a cold motor the idle sputters because some gas is condensing back to liquid by contacting the still cold intake runners...
(the carb gas spray droplets are too big {due to marginal HG} and probably too many droplets due to the too rich jets)
that's bad because that liquid gas is washing oil off the rings and cylinder walls and getting into the oil pan...

for right now till all gets sorted out,,,,raise the idle to 1000 (+?) and increase the base 2*'s,,,,"should" get you to atleast 13Hg...

the too rich jets are contributing to the low idle Hg but hard to judge how much,,,, and the black plugs are telling you it is too rich so correct the jets ASAP...

swap jets and post idle Hg with 16 base and 800

the factory engineered fuel feed curve (based on ever changing Hg present for how much gas is fed) is calibrated to include the air from the pcv to end up with a correct air/fuel ratio for any Hg condition...
pcv itself does only good things for a street driven motor,,,use it correctly for long motor life...

re: less plug gap
"recommended" oem gap is a "compromise" choice so a car can run anywhere on the planet regardless of altitude/temp/gas quality/etc...
what happens when you reduce the gap is there are more milli-amps in the actual spark which is the "heat" (aka "blue flame hot") that keeps plugs clean...
with a big plug gap the coil needs to constantly charge to a much higher KV to be able to jump the gap to first burn a hole thru the mix....
so then/next how ever many milli-amps are still left actually light the mix and clean the plug (aka just a yellow flame worth of heat)...

second benefit from less gap is the coil will last longer because it stays cooler,,, which also helps add milli-amps to the spark...

re: 24* idle timing
vacuum advance does nothing except good for a street motor...
more timing will raise Hg to make better/more power at street rpms...
set your base to 16 for long-trouble free batt/starter motor life and add 8* worth of vac adv hooked to a manifold port on the carb...

a inherent fault of any performance cam is less low street driving rpms TQ power output compared to a stock cam...
more timing does help!!!!

eric32 04-11-2010 04:11 PM

Ok guys here is an update on my engine. I took it up to my dad's house today and he has built engines for many years and really knows his stuff. Now please bare with me many people who know all this stuff will disagree at times on certain things so please be kind to me as I am a rookie and just trying to learn the tricks of the trade. My timing is already set at 16 degrees initial at idle with the vacuum advanced plugged. With vacuum advance hooked up it brings my rpm up about 100 rpm and that is with it hooked up to the timed port at the metering block. I know about timed port vs full manifold but that will be another post. During the winter time my engine idled good and did not have all this spitting and sputtering really bad like it's now doing. Never changed anything just put the one inch spacer on nothing else.

Happens mainly bad at warm up bet mostly goes away after its all warmed up. He adjusted the idle mixture screws and to get the highest idle speed change and it helped smooth out my idle. I did not have my vacuum gauge with me so was unable to see what it was doing. Ok I got it home and I wanted to check where he had them at and he said he went out a full turn which I thought would be a lot so wanted to check with vacuum gauge. I checked the screws and one was one turn out and the other was about 2.5 so I know that would not work correct and they are supposed to be the same. I turned them both all the way back in and went back out 1.5 turns. The idle mixture screws are very sensitive so turning them in either way does affect engine idle so I know they are doing there job and the transfer slot is not exposed too much.

Hooked up gauge and put idle back to 900 rpm and with idle mixture screws out 1.5 turns it now reads a steady 14 inches of vacuum for first time ever and stays there with no fluctuations like before. It seems the engine might want just a hair more on the idle mixture screws but how much is too much? I want to keep this thing as lean as possible at idle but with the best vacuum. Can't go less then 1.5 cause the motor will not idle smooth it will sputter. The missing at idle was even there when I had the pcv valve hooked up before and it made no change in that part. I thought it was the problem with my oil on plugs. Plugs are not oil fouled and still do good when running but outer ring gets black over time.

So that being said my dad said you can see on the side of the plug where it burns its a tan color so it is good where it is. The stock holley carb 600 came with 65 primary and 69 secondary but that is for a stock type motor. Like I said my brother's 305 chevy has the same carb and his motor is nothing performance wise just a smog type engine. My engine I figure would not run correct with that small of a jet setting cause it's a lot more then stock with bigger flowing heads, intake and bigger cam etc.

Will post a picture of what my new plug looks like after one day of running here after bit. Got to go to store so will be back. Thanks for the help guys appreciate it. I also got some better spark plug wires to go on it as well.


red65mustang 04-11-2010 04:43 PM

you did mount a 4 hole 1" spacer right???

rpm intake is a dual plane,,,that means each piston intake stroke sucks from only half the total intake volume area and pulls fuel from only one primary venturi for max Hg...

a 4 hole spacer maintains the dual plane design because the intake divider wall seperation under the carb is kept intack,,,usually won't cause a sputter condition....

a open (one big hole) spacer creates a huge air vacuum leak right under the carb so that now each piston on intake stroke is trying to pull from the entire intake area volume and is trying to pull a vacuum from both venturis=half the Hg pulse signal to each...

a open one hole spacer can cause sputter at idle...

the rpm intake is already a high rise/long runners design,,,you don't really want/need to make the runners longer and add more area volume with a spacer...

automotive breath 04-11-2010 05:04 PM


Originally Posted by eric32
...My timing is already set at 16 degrees initial at idle with the vacuum
advanced plugged...

Eric, if it were mine i'd run more ignition advance at idle, this would improve
idle quality and allow you to run a leaner air fuel mixture. With this the plugs will
run cleaner. If you decide to increase the initial, keep an eye on the total

How much initial advance do you have?
What is your total advance?
How much advance is in the vacuum canister?

Initial advance - ignition advance at idle with the vacuum canister plugged

Total advance - initial advance plus centrifugal advance combined; checked
at RPM where the centrifugal is full in (vacuum canister disconnected and pluged)

Check the vacuum advance with the hose connected to manifold vacuum,
subtract initial advance from this reading to determine what's in the canister.

Don't be concerned about the jet size in someone else's engine, tune your
engine for what it wants. Just because one engine makes more power than
another doesn't automatically mean it needs larger jets.

78 monte 04-11-2010 05:10 PM

I'm sure many will say it has nothing to do with it as long as the heat range is right,but I allways use Delco plugs in SB chevys. Champions IMO are only for lawnmowers and NGK IMO are one week snowmobile/ATV plugs that get tossed on a trail somewere when they foul out.
Only other plug I trust besides delco is Bosch platinums.
As off beat as it may seem thats were I would start.

carsavvycook 04-11-2010 05:48 PM

The proper spark plug heat range, and gap, will improve performance/fuel mileage. :thumbup:

eric32 04-11-2010 05:56 PM

Ok guys noted of the info. Right now I can't get a picture to upload cause it's saying it's to big and I don't know how to make it under the 2mb limit. Yes I did install a 4 hole spacer but only because I had to move my carb up cause the dual line assembly hit's my heater hose on the corner of my intake. I changed over to center hung fuel bowls incase your wondering. My initial timing is 16 at idle with vacuum advance pluged off. Rev it up and its total is around 34 by 3000 rpm. I don't want any more timing then that cause it runs nice and good on 89 octane with no pinging at cruise or even if you smash it. I will try to google and see if I can find something to shrink my picture with. Will post back.

eric32 04-11-2010 06:09 PM

1 Attachment(s)
Ok guys here goes hope this works. I use ngk plugs cause they work better for me then delco plugs. I have certain header tubes that will not clear delco plugs but clear the ngk plugs. Everyone has there picks but the delco 45ts and the ngk 6630 both gapped at .045 work the same for my engine with no difference in mileage or performance. Hope the picture works. I will have to hook up my timing light so see what the vacuum advance is doing at idle will get back tomorrow on that one.

carsavvycook 04-11-2010 06:35 PM

That Plug looks like it is running too lean. How many miles/hours on that plug?

eric32 04-11-2010 06:55 PM

It has some idle time and some town driving with about 18 miles highway. Put them in yestarday. The previous plugs I had that was in there for a month looked the same as them.

red65mustang 04-12-2010 06:29 AM

1 Attachment(s)
now that the idle Hg is 14,,,

next step/next test is re-gap the plugs to .040 and drive it for atleast full week plus...
(lol,,you would need a microscope to read a plug with that few miles worth of just normal driving)

post after a couple of days worth of miles if the idle sputter went away or is still there "after" re-setting the plugs gap...
(it's a diagnose test for next likely sputter source since it wasn't the spacer)

my $.02:
the minor amount of dry black carbon that is on the inside steel part of the plug and lower threads doesn't harm anything,,,don't worry about it!!!
(hope this makes sense,,,a oem stock/low lift/gentle ramps cam valve train geometry movements has a very tough time controlling every last bit of oil oil on the valve stems,,,a 220/230 cam configuration/motion is putting all kinds of more stresses/flexes and side loads and vibrations on everything)
heck, plugs are only a coarse thread worth of seal,,,so "how" sharp was the tool that cut the threads in the heads and on the plugs????

if/when you find wet oil/black on the ceramic insulator and electrodes,,,then you need to do some testing for the source...

"IF" you were interpeting the dry black on the plugs steel shell as a PCV oil pick up problem,,,not true...

re: choke for warm up
a proper motor warm up choke also has a cam or a solonoid on the linkage to change/increase the fuel feed to work off the primaries curcuit by giving it some throttle when engaged to match more rpms...
the amount of gas fed by the idle curcuit is a constant fixed amount regardless of rpms based on the screws...
and most idle circuits can only feed about roughly 900rpms correct amount worth of gas...

rpms go up with just the flapper closed because Hg goes up (due to the venturi air flow restriction) which makes more rotational TQ output "but" your leanest set idle just went way way lean with more rpms because the gas amount didn't also increase...
(manual flapper choke is really only intended to help get a motor to start like on a lawn mower in "start" position)

you are SMART for letting it idle to warm up!!!
COLD "is" hell on earth (!!!!) for rapid motor parts wear (with a load on it driving) as this attached chart shows....
(do note that is only a 60 hour test)

the now 14Hg idle will help the dead cold motor get to a stable idle much quicker with no choke so you can go back in the house on cold days...
rpms/2=power strokes making heat,,,not much difference between 600 choked power strokes versus 400 no stroke over a full minute of time...

LOL,,,oem cars have to have a warm up choke because women just turn the key and go!!!

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