JON242

This sounds like a repeat of my disaster last year. Those plugs that are white could be way lean. Had this happen after I changed an intake manifold. Think I had a air leak at a couple cylinders and didn't diagnose the problem until I melted a couple pistons. My engine started and ran fine, just down on power. I had almost the same drop in RPM's that you're seeing.

olysan

I'm going to pull the new plugs and take another look, I made a couple of wot passes yesterday.

JON242,

Where do you think the air leak was?

Havasu,

Makes sense if 1 & 3 look the same I'll try an ohmmeter.

shawn

Just an idea, could the outdrive have been rebuilt with different gears?

JON242

Not sure where the leak was but I suspect maybe from the lifter valley into the intake port. One of my symptoms was if I ran at WOT for about 10 seconds it would start to act like it was running out of fuel, then throttle back and it would be OK.

birdog

(except I think one or two rocker arms may be out of adjustment),

I would start here !

olysan

Here's a pic of my plugs. Same thing on 1 & 3, they look almost new. You can't see it in the pic, but it does look like they've been sparking just not igniting anything. 4 was damaged during extraction. I thought 8 looked lean when I pulled it, but it looks okay to me now.

I still haven't torn into the valve train, I'm hoping to get after that tonight.

Let me know what you guys think.

Raypanic

I had a similar problem with my 454 Mag, Last year it ended up being a bad/clogged injector. Is yours an EFI Setup or Carb? My plugs looked the same, The non firing cylinder was like new.

olysan

Mine's a carb.

TomZ

Are you sure that you have good wires going to those plugs? How about the cap and rotor? Good? There is nothing happening in those cylinders. Have you painted anything... maybe the plugs aren't grounding? You should at least have the effects of combustion on the threads like the others. Can you get any close-up pics of those plugs?

I would think that if you had an air leak it would be lean, but it would still fire to some degree and you'd see something happening on the threads. Also, with a very lean condition you'd have some damaged plugs.

And one last question (and this may be stupid sounding), but did you by chance stick anything down in the intake ports to keep out critters and such and then forget to remove them upon reassembly?

I don't think you're getting fuel to those cylinders.

olysan

I put an ohm meter on the wires last night and they all checked out, the cap and rotor look okay. I can see signs of spark when I look real close at those plugs, so I don't think its a spark problem.

I've been trying to figure out what could have gotten (or been put) in the intake runners, but I don't think I ever had them blocked. I was under some pressure to get it back together, and I'm not above doing something stupid.

I'm going to try and get the valve covers off tonight and we'll see where that gets us. If the intake vale on 1 & 3 isn't opening at all could that be the prob? Like if the rocker slipped off the pushrod?