I believe the 4160 has a 1992 stamping on the front right horn. regardless, I spent some time today spraying carb cleaner at idle in search of a vac. leak.
It was frustratingly boring until I shot the secondary shaft at the baseplate on the driver's side. I could def get an idle-up. not huge, but repeatable. I tried also around the baseplate to 'body' gasket and the baseplate to intake spacer gasket near the secondary shaft just to be sure. When i did that I got a 'pop' that sounded like a small firecracker once or twice, but not consistent, and also not 100% that it didn't get sucked thru the secondary shaft 'bushing'.
as for 'slop' in the shaft, there is some. not huge compared to some I've seen, but maybe 0.020 to 0.030" fore to aft (and a little up and down).
So.
a half hour of internet research says I could buy a new baseplate fro around $150, or I could buy a reamer and install a bushing around the shaft (can anyone confirm the secondary shaft diameter/bushing is the same as for primaries?), or some guys even say the idle-up is normal because there is never a perfect seal even with a brand-new baseplate.
discuss.
thx

 

The shafts aren't very tight to begin with and if either shaft would wear out it will be the main shaft. By the time you would buy a new reamer, bushings, new shaft and the tool that crimps the new throttle blade screws a new one would be the way to go.
What is the problem your having with your truck ?

 

Thanks, I was indeed surprised to have slop on the secondary shaft more than the primary (primary does still have the springs attached, didn't try without them.
Truck is new to me, have owned it for a month and about 100 miles.
Issue is a rough idle, and an A/F ratio that seems inconsistent. Using a tailpipe "enema" O2, I first tuned idle to max vac/smoothness, which was A/F in the 12.9-13.2 on E10. If I try for 14.1 it gets a lot 'shakey-er'.
But, without making any further adjustments, sometimes the idle A/F R will be as low as mid 11, or high 13's (engine at operating temp, choke plate wide open).
Engine is quite smooth from about 850 rpm on up.
compression and leakdown very even (see the initial oil analysis thread in this subforum).

 

Sounds like something is causing it to run rich at idle, which could be a lot of things.

 

It probably won't idle well at 14:1 most engines are that way and will idle best MUCH richer at around 12.5-13:1. That's normal. You might try opening up the plug gaps to .080 or so and see if you might get it to idle a little leaner.

 

Check float levels, if they are ok then check the power valve in the carb.

 

thanks Mark
I did already change the primary needle/seat and adjust the float (it was too high).
I will do same on secondary side, I suspect float is too high, or needle/seat leaking---although I do not have a big outflow from the rear sight port it does seep out from that screw. parts are enroute.
But what is the thinking on the power valve? ruptured and leaking at idle? regardless--should not be as I just replaced the PV when I changed the pump diaphragm and cleaned primary metering block (and did the primary needle/seat and float adjust).