Another electrical/ignition gremlin!

dlampe · #1 (**permalink**) 06-03-2011, 09:51 PM

I haven't had the car out for a little while. The last time I drove it I fouled #4 and #8 plugs. I switched plugs and took it for a test drive tonight and I am still not firing consistently on those plugs. I have replaced the plug wires twice prior to this. Both sets were MSD wires and the car barely has 200 miles on it. I replaced the plug wires because #1 and #4 were fouling out. I am running a duraspark distributor with the 6AL2 box. I have replaced the cap and rotor as well.

I am probably going to order a new MSD dizzy unless someone has a better suggestion.

Oh yeah, I'm running Weber's.

RICK LAKE · #2 (**permalink**) 06-04-2011, 03:15 AM

Dlampe Dean start with those carbs. Are the sparkplugs gas fouled or oil fouled? they look about the same. Any gas smell from them when removed? Swap to good plugs with #1 and #4 if new plugs foul, it's not the ign system. With the methonal in the gas and it is eating rubber hoses, I am thinking possible problem in the main curcuit of the carbs and they are leaking down into the cylinders. You don't want to keep doing this of washing down the cylinders. Can you swap carbs with know good ones?? Do you have a GOOD spark tester? this is one that makes the spark jump about 1". You are also looking for a good bright spark. You can unhook the wire from the spark plug and use a test light to ground to see if the spark is bright and jumps also. With the car sitting for a while, I am thinking gas problem. If not, you are looking mechanical. Possible valves not sealing in the heads if the motor sat for months without lossening the rockers. Is there any backfire in the intake or tail pipe?? A picture of the plugs will help. Rick L.

vector1 · #3 (**permalink**) 06-04-2011, 04:26 AM

back cylinders are probably the hottest... maybe a carb problem or leaking intake runner into the crankcase, doesn't sound like electrical. is the fuel line intake at the back and where is the pressure reading taken, may be a pressure differential thing, those things are touchy, touchy, touchy.

dlampe · #4 (**permalink**) 06-04-2011, 05:30 AM

Here's why I don't think it is fuel. The weber carbs will foul 2 plugs at a time if the pressure is high because there is one needle per two barrels and the other plug is good. I have my pressure regulated with a traditional Holley low pressure set at 2.5lbs and a Kinsler bypass regulator set to 3 pounds after the carbs in the return line for extra insurance.

Rick, I don't have a spark tester. These were brand new plugs. I have had a similar problem with fouled plugs since day one but I have always thought it was just the carbs. I have been through these carbs a hundred times and I just don't think that is the problem. They don't have rubber seals that the ethanol would eat up. I guess I could switch the carbs around and see if the problem follows the carb. If it does, then they are gone! If it doesn't, what then?

The timing light flashes on both wires but when I squirt water on the header, it clearly isn't as hot as the others.

jhv48 · #5 (**permalink**) 06-04-2011, 06:27 AM

Fire up the engine and pull the plug wire from each of the offending plugs one at a time. Hold the plug boot next to the block and look for a spark to jump. Or you can just touch the end of the boot with your finger. (when you wake up, proceed to the next plug and see if there is a spark to it as well).

If there is spark to both plugs, and I bet there is, then you have a fuel delivery problem. Go back to the carbs. Could be the same problem to two separate carbs.

RICK LAKE · #6 (**permalink**) 06-05-2011, 04:31 AM

Dlampe Dean Hate to be the bad guy, If the carb change doesn't change the location of the spark plug problem you are looking at valve train issue. IS IT POSSIBLE you missed a shift and banged the rev limiter????

You may have bent the valve stem. The oil seal will not hold the oil from being sucked into the port. You could pull the intake manifold and look at the valves (intake) and ports for oil in the ports or on the valve stems. It might look like a heavy carbon buildup. If you can get a bore scope this may be the easier way to find the problem on the intake side. Also need to remove the headers and look on the exhaust side too for the same issue. Look for more than the normal carbon build up in the exhaust ports. If this shows a normal look, a compression test would be next and looking for a leak cylinder. If this show nothing, a leak down check would be last. It's possible that the piston rings ends line up and are sucking oil through the end gap. Most oil rings are low tension these days. Would still like to see the plugs, Rick

dlampe · #7 (**permalink**) 06-05-2011, 06:13 AM

I pulled the #4 plug and it was clean. I assumed it was fouled like it had been in the past. At that time I was running 165 mains and now I'm running 155's. I saw the fire from the exhaust pipe and assumed rich. Today I turned the mixture screws out a full turn, (It was at 5/8's) and the popping went away and the car drove a little better but at idle it was way rich. What about going to a 70 idle jet from the current 65 and turning the mix screws back to 3/4? The holder is a 100. I feels like it ran better with more fuel in the circuit. What do you think? You can hear the mains come in and it runs great over 3000 rpms.

I did switch the carbs around and now it seems to run better. I can't tell you why but it does. There was some oil on the intake valve just sort of puddled up in there like it had leaked past a seal on #4 but the plugs look good. There was enough to stick a screw driver down in it and pull out a drop.

You guys are probably right and it is likely the carbs. The LM1 A/F seems to think I need more fuel it the transition.

RICK LAKE · #8 (**permalink**) 06-05-2011, 05:10 PM

Dlampe Dean from what you are saying, sound like junk in the carbs. If you are richening the carb for the one hole and the motor runs better there is something in the primary jet or holder that is cause less fuel than the cylinder needs. Sometimes just swapping carbs or injectors the crap in the carb or injector moves and stops the problem. If the carbs got to dry this is very possible to happen.
As far and the oil in #4 sound like a leak seal or bent valve stem. The carb washes down the valve and you will see only a little oil. If the spark is strong enough it will burn everything in the cylinder, air/fuel and oil. The plug over time will look black but still fire. The other thing is the O2 sensor will get the wrong readings of the A/F mixture coming out the exhaust. The oil will slow the readings and say to lean out if the readings are low.
Try and replace just the valve stem seals for cylinder #4 and see what happens after you install new seals. Rick L. Ps you can do this in the car without pulling the head.