#1 Exhaust manifold temperature variation
Posted: Wed Apr 28, 2021 12:41 am
My 62 3.8L runs the original HD8’s on stock manifold. No matter what changes I make to carbs, the back three cylinders run around 600F and the front three in the 300 degree range. Back three plugs are carboned along with first cylinder. 2nd and third (from front) no carbon.
Setting jets down from bridge .060” backfired badly and finally smoothed out and pulled stronger at .140” down.
The needles are “U”. I believe stock needles are UM?
Have set all three based on undercut ring and measured to be same length. Butterfly’s were individually set, checked with velocity gage and linkage reattached and synced .
Timing was set with dial back to 32 degrees, vacuum disconnected and full mechanical advance (2500 rpm).
Valves have all been checked as well as compression.
I am at a loss. This does not seem normal and I am afraid 600-700F may be hard on valves.
Setting jets down from bridge .060” backfired badly and finally smoothed out and pulled stronger at .140” down.
The needles are “U”. I believe stock needles are UM?
Have set all three based on undercut ring and measured to be same length. Butterfly’s were individually set, checked with velocity gage and linkage reattached and synced .
Timing was set with dial back to 32 degrees, vacuum disconnected and full mechanical advance (2500 rpm).
Valves have all been checked as well as compression.
I am at a loss. This does not seem normal and I am afraid 600-700F may be hard on valves.