Have a .030 over 350 with iron eagle 180 runners and 64cc chambers speedway cam 214@.050 in 224 ex .442 in lift .465 ex 0 decked with cast flattop 4vr holley contender 300-36 z28 style intake with a holley 3310-3 carb carter mechanical fuel pump has even compression across the board at a high 190 been running race gas mix for the 2500 miles i got on it now in which it was burning a little lean thru the first tank full then i got it jetted right and havent had any ill effects untill recently,today it started popping and sputtering on excelleration so i checked the compression and it was even all thru at 190 but the #6 plug was black sooty with gas,not wet but sooty,changed the plug and was good for 3 miles then happened again started popping and running like sh**. Changed cap rotor wires and swapped distibutor ,pulled valve cover to eyeball valve movement and there moving the same as the others,thought maybe flat cam, but all looks to be kosher didnt measure but the valves arent ticking and lash stayed the same,also its got a jackson gear drive so the chain isnt the problem,cant see any visual breaks in the valve springs,im stumped,its just # 6 the rest are firing fine by the looks of the plugs,changed plugs on 6 4 times only good for 2 to 3 miles then back to popping and sputtering,seems to get better as rpm goes up,but on the bottom its bad,the accelerato pump shoots fine,was possibly thinking the valve spring lost tension on that cylinder but it gets better in the mid range.never had nothing like this,help me out i stuck going to leakdown it tomorrow.thanks man-a-fre
Not sure, but does the intake manifold have a vacuum port in the #6 intake runner? If so, is that by chance connected to the vacuum modulator on the trans(assuming you have an automatic.)? All the other sparkplugs look alike except for #6? or are any of them getting dark? Are you sure it is gas and not oil on the plug? Might possibly be the intake gasket is bad on the #6 port and it is pulling oil into it from the lifter galley? Does it do this free reving the engine or only driving it? Are the plugs that you changed also black/sooty or just misfiring again after you drive it 2-3 miles?
That vacuum port idea is interesting. I have heard of transmission vacuum modulators having ruptured diaphragms, which can suck transmission fluid up into the intake. Maybe that spark plug cable for the number 6 cylinder is weak for some reason, like the distributor end connector is loose, or the core is torn up, or it's shorting to ground. This sounds funny, but try running the engine in complete darkness. If it's dark enough, you can see the spark plugs flicker with a blue glow each time they fire. If there's a short to ground, somewhere down the cable, you'll be able to see it. If the spark plug stops firing, you'll be able to see that too. If you put an inductive timing light clamp on the number 6 plug wire, you can shine the light on the harmonic balancer and see if you're getting a steady fire out of it. The exhaust crossover passage runs near the #6 intake runner I think, so I wonder if there could be a leak somewhere and you're sucking exhaust into the #6 cylinder. Good luck, it sounds like a tricky problem.
Are you sure you just don't have a bad grind on the cam...it's possible (sorry just skimmed through story don't know the situation). Does the #6 plug go out due to mass mounts of oil consumption?
No vac port on 6 have the modulator plugged into crb at manifold vac in the front baseplate,all the other plugs are burning great,ill leak it down today i guess.i suppose the intake could be the problem,the plug looks like you took a acetylene rich torch too it right away,but when its not under load in park it doesnt pop or seem to have any ill effects.Thanks for the ideas so far guys.
I'm kinda with Joe cool on this one. I'm runing a holley contender and i noticed when i switched over from the intake that I made to the contender that the #5 and the #6 have a tendency to be a little richer than the rest i chalked it up to intake design. But my difference isn't as drastic as yours seems to be. How new is your holley carb? On a Holley you never rule out the power valve, the newer ones all have a blow back protector but that doesn't keep 'em from going bad. Thrust me all I run is holleys on my stuff. That doesn't sound like the problem but I just thought I'd throw that in. Anyway getting back to it if you have ruled out an ignition problem then I'm gonna hang with joe on this one.
thanks guys you called it,i leak checked today leaked 1% so all good there,intake leak on top side and oil side of 6 used the propane torch trickto find it on top,anyway i changed the junk mr.g paper intake gaskets to felpros all fixed.thanks again man-a-fre.
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