Four hole spacer on cold engine

[i82much]

Hi all,

I have a 72 K10 with a 396, iron block and heads, Performer intake, functional heat riser valve with open heat riser passages in the heads. Really basic stock-type engine. I have a four-hole, 1 inch phenolic spacer on the engine, I put it there a few years ago because I was concerned about getting too much intake heat.

I have a manual choke on my truck and I notice a really big difference in engine RPM cold vs. warm with the choke off. In other words, if I start the truck with the choke, let it run for a minute or two, and then open the choke, the engine might idle at 900 RPM. Once the engine fully warms up and heat soaks, the engine might increase to 1300 RPM or so.

I have checked all over for vacuum leaks and don’t see any, there’s nothing binding in the linkage or throttle blades that is adding more air. The engine just picks up a bunch of RPM at idle for some reason when it heat soaks.

Is it possible that the spacer is making fuel fall out of suspension when the engine is cold because the fuel has to travel further in the cold intake?

Thanks!

[rp930]

Oil is still cold and slows down the idle.

[Firedome8]

Check the timming between cold and warm.

[mag2555]

A stock type engine as you call it should not need to idle at 1300 rpm, you have a vacuum leak taking place somewhere when the motor is up to temp, or the mechanical advantage shaft or weights are hanging up the timing as stated in the above reply.

Old GM points type and HEI distributors are known for the advance shaft grease breaking down into thick crud that hangs up the shaft and in turn the advance once the motor heats up.

I have seen 3 cracked BBC intake manifolds in my time before!

[bobmc]

what is the carb? how old is it? how old is the vehicle linkage? issue sounds like fast idle cam and linkage

[Dan Timberlake]

Generally Carb adjustments like idle and idle mixture require the engine be at at operating temperature.
"http://chevy.oldcarmanualproject.com/ch ... om051.html"

The fast idle provided by the choke's fast idle cam is adjusted separately.
Sometimes strictly mechanically, some times by the actual idle speed when "on the cam."
http://chevy.oldcarmanualproject.com/sh ... 06m25.html