Well if there's anything that can be considered "good news" in all this, it would be the fact that you have found the smoking gun to your tapping and lash pads flying out.   

Got the carbs, intake, header and thermostat all removed yesterday. You can clearly see the valve seat dropped down in #4 intake....

Once my chain wedge shows up I’ll get the head off. 

Head is off. On the plus side I found that I do have the larger valves in this E31 Head.   Also the bore measures 87.5. So it’s bored out a bit. 

 

Well there's your problem! Whoever did that head work screwed something up.

It's really a shame that the valve missed the relief in the piston. I wonder if that's because of the larger valves? The stock valves were smaller? And might not have hit the piston?

Nice metal head gasket. Looks like it was sealing well. And head studs/nuts instead of head bolts. Clearly someone made a lot of changes in there. Too bad they weren't all done correctly! 

I think the seat hit the piston...thus the wider diameter that hit.  Missed it by that much.  Piston damage is actually very minimal. 

Yeah, the motor was built with all the right stuff......but the dude was asleep at the wheel when he installed that particular seat. 

I'll hand it off in the next week or so and then we'll go from there. Honestly...I'm just glad to have found the problem and will rest assured that it will all be good from here.   Heck, we might even get this thread back to being about tuning carbs sometime. 

 

Stay the course through the fog a very wise man told me. 

Wow that exhaust valve sure does look to sit deep into its seat but I am no head expert for sure.

Just never saw one ground like that assuming new valves and seats.  An old stock head with a couple past valve jobs, then yes.

The valve seats look to be so tight fit that there is no interference fit between them. See what the head experts say.

Head has been dismantled, inspected and a new valve and seat have been ordered.  My mechanic thinks that the seat may have gotten installed slightly off and was eventually just knocked loose by the valve. 

Should have it back within a couple weeks and install. 

 

 

Good luck, and lets hope it's as simple as pressing in a new seat. 

Head is done. New seat and valve installed. Everything else checked out fine. Gotta get it back and install everything once again. Then hopefully we are just back to tuning! 

 

Ok...where were we? Oh yeah...tuning webers....lets get this thread back to that!

IMG_5211 by blodi, on Flickr

Wow they look great!

 

While you were fixing your Z @duffman  and I were optimizing his setup which is similar to yours (L28 w 40DCO 151).  Here are his settings:

  Weber DCOE 40 151

 

  choke - 32 mm

  Auxiliary- 4.5 mm

 

  Float needle valve - 1.75

  Fuel level - 27 mm

 

  Idle jets -  (drilled: 60F9  with air drilled to 150  (Equivalent to 60F15) )

  Idle mix screws - 2 1/4 turns out

 

  Emulsion tube - F2

  Main jets - 135

  Air corrector jet - 161 (drilled)

 

  Pump jet- 45

  Pump exhaust - 50

 

  He is setup for flat 13.3 A/F WOT from 3000 to 6000

  Cruise at 30mph is 14.5

  Cruise at 60mph is 14.5

  Idle is  14.5

 His car is set up like EFI!