A while back a head gasket went bad on my FE 410 and it was blowing all the water out the pipes and I got it real hot a couple of times trying to get it home. We pulled the heads off and replaced the gaskets and had the heads checked for cracks just in case and it turned out that I had two burnt exhaust valves and all the guides were bad. So i had both the heads rebuilt. We slapped it back together and it ran like it did when i first built it for about 20 minutes and all of sudden it just started running really rough, no power and sounds like it's missing. It runs like it did when it was trying to burn water but it's not using water.zIt will start and run without getting hot and such, but it accelerates hard like it's fighting a miss or something and it just wont fire smoothly. The coil is new, distributor is rebuilt, cap is new and clean, rotor is new, plugs and wires are all new and where they are supposed to be. It is electronic ignition. I have never witnessed a motor run so poorly, and it did it while I was on the highway, going from perfect to crap just like that. I don't think it is a vacuum leak, at least i have never seen a vacuum leak make a motor run like this. Does anybody have any suggestions? i need to get this thing right because it's my daily driver. I left it idling and went to each plug and pulled the wire one at a time but nothing seemed out of the ordinary.Help?

 

Just a thought, but could there be a piece of loose crud blocking one of the main jets in the carb? That would make 4 cylinders run really lean. How's the timing chain?
Just a couple of ideas.
Greg

'77 F-250 Camper Special 400ci driver
'76 F-250 Supercab 360ci current project
'71 Mach I 429CJ in storage
'79 F-150 for parts
huct on foniks wurkt fer me

 

The timing chain was new 2.5 years ago when I built the motor and it hasn't seen many miles. I bet the whole motor has just over 10,000 miles on it. It could be a carb problem, i'll have to play with that.

 

It could be the carburetor! But I always start with ignition when trouble shooting an engine. I would have a careful look at the distributor, electronic ignition components and the coil. I expect that whatever it is, it is affecting all or most of the cylinders. I'd do the obvious fuel system checks, like cranking pump pressure, clean filter, crap in the tank and so on. But like I said I always start with ignition.
William in Atlanta

 

Check to make sure the intake manifold is not leaking where it joins the head. I put a new 390 together and it started running really bad. Then, when I would decelerate from highway speeds, it would SMOKE like heck!

The intake manifold gasket hadn't seated correctly because the bolts were too long and had bottomed out in the had. It was sucking up oil under high vacuum.

Stupid on my part, but check to make sure it's not an intake leak.

ak

 

Well it does smoke now which it never did before and when I had the heads off the cylinders and rings all looked in good shape. It also has a very irregular idle, it will go way up, then it will slow down, almost die and back up again. I put quite a few miles on it today still trying to figure it out. It definately appears to be vacuum to me. I drove it about 60mph at 2500rpm or so for about 30 miles and when I got home I let it idles for a bit and clouds of oil smoke began rolling out. #8 cylinder also appears to be dead for whatever reason, it has spark at the wire but once you put it on the plug nothing happens. I have tried several different plugs and nothing. My only guess is it is getting flooded out because the plug smells like gas bad when I pull it out. I guess i will pull the intake, AGAIN, and try resealing it. If anyone has any more ideas i really need as much help as i can get.