File this one under "Do I feel stupid, or what"

[Matt Haas <mhaas@xxxxxxx>]

One of the nagging problems that I've had with my American almost the 
entire time I've had it is a rough, hot idle. I've done a bunch over the 
years that has sneaked up on solving the problem but since I got back from 
Kenosha, the problem has gotten much worse and at times, it's been more 
like riding a mechanical bull than sitting in a Rambler with a stockish six 
cylinder.

Anyway, outside of rebuilding the motor, I've done the following to the car 
to try and fix it:
- Removed the heat riser valve (was stuck half open) and had the faces of 
the manifolds machined flat, double checked the seal by spraying with WD-40.
- Cursed at it
- Noticed that the dwell angle was all over the place at idle so I shoved a 
Pertronix Ignitor in it
- Cursed at it
- Put the correct carb back on it (it had an Economizer with a bad choke 
coil when I got it). Checked for leaks again with WD-40 -- made no 
difference in idle quality.
- Cursed at it
- Fiddled with carb jetting, idle mixture, and timing. Checked for leaks 
again with WD-40 -- made no difference.
- Cursed at it
- Put a rebuilt distributor on it (or more correctly, put the rebuilt 
distributor's guts in my housing since the housing I got was messed up)
- Cursed at it
- Fiddled with idle mixture and timing
- Cursed at it
- Replaced the plugs, wires, and cap
- Cursed at it

None of these things really fixed the problem (the distributor sure helped 
with acceleration and high speed operation) but my cursing skills have 
improved quite a bit so it wasn't all for nothing.

I had actually tried spraying WD-40 at the joints between the carburetor, 
manifolds, and engine a few more times than what I mentioned above and it 
never made a difference until today so I had pretty much written off 
"vacuum leak" as a problem. What I did different was drive the car first 
until it started idling rough. I then popped the hood and first thing I 
checked was the choke. It was wide open so I started looking around and it 
looked like there was a gap between the manifold and the gasket at the #3 
cylinder. I got out the WD-40 again and gave it a good spray and sure 
enough, the engine smoothed out quite a bit for a few seconds. I sprayed 
WD-40 at a few other places and saw improvements in idle quality again so I 
got out my torque wrench and started tightening bolts. It seems what I did 
when I had the manifolds off almost 5 years ago was to fully tighten the 
bolts that only go into the exhaust manifold and just snug up the rest of 
them. The bolts that attach the intake manifold were a full half turn 
loose! I torqued them to 25 ft. lbs and reset the idle mixture and took it 
for a test drive. I'll need to go recheck them after the engines had a 
chance to cool down and I'll probably have to replace the gaskets to get a 
totally smooth idle but man, what a difference a tight intake manifold made!

Matt

mhaas@xxxxxxx
Cincinnati, OH
http://www.mattsoldcars.com
1966 Rambler Rebel
1968 Rambler American sedan
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