What Causes this?

[724x4a/cchevy]

Is this caused from running lean? The truck is missing and i cant figure out why. Pretty sure this is why. These came off the driver side, so i think that side is running lean or something. These are really good quality plugs(or so im told). NGK v-cut electrode. The timing is dead on. The truck has been converted to HEI too. Thanks for the input.
Justin

[O'l Buck]

They look a little lean to me.

[1fun71]

yeah those plug have been HOT

make sure your running a plug in the right heat range, or you my have a intake vacuum leak, low coolant, sticking valves etc... etc

or just to LEAN

[724x4a/cchevy]

hmmm they are the plugs that o'reilly's said fit my truck. I dont think the block itself has been hot. at least not since i replaced these about four months ago. It does have at least one worn valve guide because it smokes on initial start-up. Surely that wouldnt be it? That only validates one of the plugs. Possibly a vacuum leak..but most likely lean. How much do you guys think i should turn it counter-clockwise? These quadrajets have adjustments for the left and right side banks dont they? Seemed like they have two screws at the front one on each side.

[jeffspower]

I disagree. Not lean, or hot- but RICH. Powdered- looking grey covered porcelin is unburnt fuel. White would mean lean. Shiny glazed would mean too hot of plug heat range. The grey unburnt fuel on the porcelin could be making the voltage flow thru it to ground rather than jumping to the electrode & creating a spark.

[1fun71]

been awhile since I messed with a q-jet but i think turn both mixture screws all the way in and 2 1/2 turns back out on both for your baseline setting. then go from there see how its running. OH and be sure the count as you screw em' in to make sure they where the same and how many turns they were.

[1fun71]

Jeffspower I think you are correct I didn't even notice the insulator was covered in soot that would indicate rich. ( this is why I'm not a mechanic)

[jeffspower]

Here's a link to some good info:

http://www.4secondsflat.com/plug_chart.html

[724x4a/cchevy]

kinda looks like #4..The white residue IS more like a powder. i can scrach it off. So you guys think it is running rich?

[eedgell]

The air/fuel screws are for idle only, so does the truck idle alot or does it run mostly, highway speed I mean. You can get confused easy on adjustments like a dog chasing it's tail. When tuning a carb and looking at anecdotal evidence you have to be careful. Run the truck at highway speed a while 20 minutes atleast, then look at the plugs and such. Give that engine time to talk to you. If at idle for long periods of time with signs, adjust the air/fuel, but if at running speed and temp with signs, look at the jets and meetering rods. From there its cap, rotor, wires, plugs, coil, ect.... Light is usually lean, dark is rich, but high idle time or stop and go can confuse this analysis.

eedgell

[jhow66]

What kind of miss? When? Under load? Cruising? Idle?

[724x4a/cchevy]

its missing all the time. I'm not sure if it is a plug wire or what. It just started doing this lately. The plug wires were brand new too not that long ago. If i take the vacuum advance off it usually stops and it seems to me that the timing advances at a fairly low RPM. I have the timing set at idle where its supposed to be. but as soon as you give it any throttle at all it jumps off the chart. I have put a Mr. Gasket spring kit in it with the heaviest springs and it still advances, what i would consider, too rapidly.

[GREASEMONKEY72]

looks oil fouled to me and the 2 screws on the qjet are for idle only but if you do adjust them be sure to count the turns in so you know and back them each out 3 turns, i would clean them up real good and put them back and see if the miss is still there or not

[hgs_notes]

Doesn't a miss sometimes indicate a bad dizzy cap? Check the contactors in the cap to see if they are eroded or corroded. Sometimes if they don't seal tight, moisture is also a cause for misses.

[mnunn454]

First, while the plugs are out I'd check the compression to see if everything's okay there.

I'd also check the carb if it's not new. Sometimes Q-jets get their fuel metering needles stuck.

If both of these are good, then test the wires with an ohmmeter, add a new cap and rotor and then test the the coil and the module and pickup coil. (Or swap the dist for a known good one and see if the problem goes away)


Hope it helps.

[cooters]

advance the timing a few degress, if your timing is behind it will misfire

[eedgell]

sounds like something is not right in your timing advance? Might look at the vacuum hose to the distributor for rot or cracks causing a leak, and possibley replace the vacuum module? Or if you have a spare distributor, try switching the two.

[jhow66]

At idle are you hearing a "pop' "pop" out of the pipes? If so this is usally from the time being to high. Are you setting the time with vacumn hose off the advance? With engine at idle,remove hose from advance. Does engine slow down?

[Eichorst69]

I agree with jeffspower, it's running "rich", not lean!
Check the carb, looks like it's dumping too much fuel. The foam floats will absorb fuel overtime which causes them to want to sink and dump more fuel. You can tell if the foam float is bad by it's weight. Usually if the float is bad it will want to load up at idle and want to stall.

Did you recently put those plugs in?
If so, could you have crossed a wire?
Maybe the running rich and the miss are two separate problems???

Rob

[PanelDeland]

Just a short note on plug reading; In the back of some(if not all)Haynes service manuals,there is a plug reading chart giving pictures and descriptions of different 'plug burns'.Some parts stores also have one in a short pamplet.

[Jim_PA]

If you guys (some of you) think those plugs are lean... you should see how lean mine are!!!1

[eedgell]

I dont think they are lean, just look at the carbon around the electrode! I do think there is a timing issue, or too rich on the carb. Still never answered does it idle alot?

[724x4a/cchevy]

sorry i have been away from the computer awhile. Yes it does idle alot. In fact that's about all i have had it doing. This is a truck that im getting ready to sell and just got it running in December after sitting for about 15 years. I havent even taken it out on the road yet for any long trips, just around the block. I have swapped HEI caps and no difference. I think there may be something wrong with the vacuum advance. We cleaned and re-gapped all the plugs and had one that still wont fire. I think the plug just went bad or something. I went around with a good plug and checked spark at each wire. All are good. I turned the driver side idle mixture in 1/4 of a turn to compensate for the richness. I havent been able to check and see if it's still missing because we didnt have any spare plugs. This is finals week at MU and i guess this is going to have to wait till at least Friday night oh well.......Thank you guys for all the help!!!!

[67 cst swb]

Ok, here's the extent of my tuning knowledge...
1st... make sure the #5 & #7 spark plug wires aren't touching... they are right next to each other in the firing order... 1 8 4 3 6 5 7 2 ... so, they crossfire very easy......
2nd timing... I've heard and seen... start your timing as 10 degrees.... go out on the street, from a dead stop... put in first gear, hammer the throttle.... it should be sluggish... you won't need to stay in it very long to know... go back advance it 2 more degrees... repeat the hammering it from dead stop. advance 2 more degrees, repeat, etc... Once it "CLATTERS" on exceleration... back it off 2 degrees and leave it there...
3rd... adjust your idle screws... pull off dist vac line from carb... plug in vacumm gauge... and adjust idle screws until most vacumm is achieved starting at that 2-1/2 turns out mark... try not to get the screws any more than 1/2 turn difference from each other...

Anyone else heard of or used this...
A drag race friend of mine uses this all the time, says that's how you get the most performance and Mileage from an engine... he says factory specs are exactly that "factory" most engine aren't factory, give the engine what it wants, it will then be happy and give you what you want...

[eedgell]

724x4a/cchevy: if you have been sitting for a long time, then the evidence you have shown is anecdotal. mainly because some trouble could have been pre-existing, and some new.? I would replace the plugs first, just because I dont trust ngk, then go from there. Sometimes these kinds of troubles cost you alot trying to track them down, and after time setting it is usually more than just on thing that is wrong. Remember, time is the enemy of most things, and in your case they have all aged together. Just as a side, how old is the fuel in this truck now? Our fuel today is not the greatest to begin with, but if it sits for long periods of time, it can cause all kinds of "symptoms" when touble shooting. If its old, more than a year, drain it out, and start with fresh. Just some thoughts. Good luck!!!