Calling on the wisdom again, I'm stumped

[D.Hearne]

The push rods are stock and the rockers are stock replacement 1.6 ratio. I think that should be all right.

Those may be stock replacement rockers, but you also said they were roller tipped, because of this fact, they may be stock replacement 1.6 ratio rockers, but they also could have also altered the geometry, making the pushrods either too long or short. I would go back and check to see if the geometry has been altered. One other suggestion, is to pull the spark plugs to verify that none have had their gaps closed. I had a 400 awhile back that I had pulled from a F100 and replaced by a built up 400. After about a year, I swapped those engines back, wanting to sell the truck. To make a long story short, the original 400 had a dead miss which puzzled me. I finally isolated the miss, and pulled the plug on that cylinder, the gap had been "bumped" closed, from handling the heads around the shop. Opened the gap, and the miss disappeared. If all else fails, you could posibly have a vacuum leak in the bottom of one of the manifold ports.

 

[Cdaniel]

Are you sure your plug wires are installed correctly? I, and many who are way more experienced than me, have made this mistake, especially on 7 and 8. It is worth checking.

Thanks for questioning my sanity
I just went and checked, I wish I could say that was it but no, my curse continues.

 

[Cdaniel]

Those may be stock replacement rockers, but you also said they were roller tipped, because of this fact, they may be stock replacement 1.6 ratio rockers, but they also could have also altered the geometry, making the pushrods either too long or short. I would go back and check to see if the geometry has been altered. One other suggestion, is to pull the spark plugs to verify that none have had their gaps closed. I had a 400 awhile back that I had pulled from a F100 and replaced by a built up 400. After about a year, I swapped those engines back, wanting to sell the truck. To make a long story short, the original 400 had a dead miss which puzzled me. I finally isolated the miss, and pulled the plug on that cylinder, the gap had been "bumped" closed, from handling the heads around the shop. Opened the gap, and the miss disappeared. If all else fails, you could posibly have a vacuum leak in the bottom of one of the manifold ports.

I'm pretty confident the rockers are up to spec as the symptoms were present before and after I installed them. But I'll recheck the mfg info.

Plugs should be good, just finished re gapping them while I did a compression check.

Now, this possiblity of an internal vacuum leak still troubles me. It's been brought up before. I've tested pretty thoroughly for external vac leaks. Even discoverd a leaky modulator on the transmission. I've tried the propane enrichment trick for an internal leak, but it didn't seem to make a difference.

Do you know of another test for internal vac leaks? I sure wouldn't want to tear it all down for nothing.

 

[D.Hearne]

I was going to suggest injecting Propane into the crankcase to leak test, but never having done that, wasn't sure as to the sanity or safety (things go BOOM ) in doing so. I guess you could try that with the valve covers removed and injecting small doses thru the pushrod holes, while the motor is running, if there was a vac leak in an individual port, it would likely show up doing this. What intake/carb spacer combo are you running ?

 

[Cdaniel]

I was going to suggest injecting Propane into the crankcase to leak test, but never having done that, wasn't sure as to the sanity or safety (things go BOOM ) in doing so. I guess you could try that with the valve covers removed and injecting small doses thru the pushrod holes, while the motor is running, if there was a vac leak in an individual port, it would likely show up doing this. What intake/carb spacer combo are you running ?

The intake is pure FoMoCo 1966 cast iron and the spacer is an aluminum slab about an inch thick with a PCV port.

I was dubious about the propane too. But a respected mechanic friend of mine assured me it would be all right. I belive its fairly sensitive, I shot it down the oil fill and within seconds I had an RPM change. I thought I was on to something until I realized the PCV was still connected and sucking all the propane in.

 

[slackr]

wet distributor cap? suckin tranny fluid thru the modulator? a bad plug or two? float level off?
i'm just spoutin off, i figured you would take any stab in the dark at this point...

 

[Cdaniel]

wet distributor cap? suckin tranny fluid thru the modulator? a bad plug or two? float level off?
i'm just spoutin off, i figured you would take any stab in the dark at this point...

I've been thinking the dist cap is the only ignition part I haven't switched out yet. Though it is new. Cheap enough to try.