1965 tripower idles faster after warmed up
 

I have a butler built 65 421 and restored tripower by Mike Wasson.
My question is it idles around 700 RPM when I first crank it. After it warms up it idles at a 1000 RPM. Is this normal? If it is normal the why does the motor try to keep running when I shut it off?

Doesn't sound like your choke is working properly. Just one reason. The first thing I would check

Check for vacuum leaks.

If the choke is functioning properly, it should idle around 1700 rpm when first started (fast idle cam). When the engine is started and the choke pull-off sees engine vacuum, blipping the throttle should bring the idle down to about 900 rpm until the choke spring sees some engine heat from the choke heater tubes. Then, the idle should drop to whatever you have it set to with the idle stop screw. With a fairly mild cam on a 421, idle should be around 700 rpm.

It sounds like your choke may not be closing when the engine is cold, so idle mixture is a too lean. After the engine warms up, and can run on a leaner mixture than when cold, idle speed increases. I would expect this would also result in backfiring and poor throttle response when the engine is cold.

There may be a vacuum leak complicating the problem as well, but confirming whether you have an operational choke would be the first step in troubleshooting.

Run on is usually associated with low octane fuel for the engine or the idle is set to high.

Dick, you really know your stuff!
You described exactly what is happening at start up.
I screwed up the choke setting by listening to a so called mechanic that told me I should set the choke wide open cold especially in the summer.
I am learning this stuff the hard way.
So tell me the proper way to set the choke.
While motor is cold do I adjust it fully closed?
Thanks so much for all you guys help!
I don’t know what I would do if not for all of you guys answering my questions.

Adjust the choke dial so the choke closes when the engine is cold with the engine shut off. There should be gentle spring pressure holding the choke closed.

You need to open the throttle each time you make an adjustment or check the choke spring tension. The goal is for the choke to be fully closed at startup and wide open after a few minutes running time.

Great!
I will set it like you said and I will let you know the outcome.
Thanks!

I have the choke set correctly thanks to Dick.
This has solved most of my issues except the fast idle after warm up.
I am pretty sure that the hot idle compensator is the reason for that. Idle seems to be fine until I start hearing the whistle from the hot idle compensator.
I guess I need to pull the carb and plug the compensator.

I don't remember the idle speed going up when the hot idle compensator opens. But, that's the most likely cause of the increased idle rpm and the whistle.

Let me know how it works out.

Your problem is likely a too rich idle mixture at operating temperature. The hot idle compensator adds air, mixture goes leaner...& rpm increases.

Geoff, that's a likely possibility---that may be fixed by simply turning in the idle screws on the center carb base.

Dick, How much would you turn the screws? 1/4 turn maybe?

You turn the idle screws for maximum vacuum, which will also be maximum rpm at idle. Do this when the engine is hot.

OK, I give this a try.

Update:
I adjusted the idle adjustment screws in by about 1/2 turn. It appears I have solved the fast idle at warm up. Time will tell. I will keep you guys posted.

I'm having similar issues, hoping to revive an old thread.

About how many turns out did you end up with this all?

Have you looked to see that the fast idle cam is rotating clockwise as the engine warms? I’ve seen situations where the choke thermostatic spring is backwards, actually closing the choke, increasing idle speed.

Check that out before you do anything else.

My MSD distributor went out and I replaced it. I also removed front carb so I could get better access to idle screws and I adjusted the choke a little more to the left. After all that it run as it should. Not sure if all of it was contributing to the issue or not.
Ideas at about 700 RPM hot and cold after fast idle is complete. No rich smell out of exhaust like I was getting.

I forgot to mention that I plugged the hot tile compensator with a 1/4” plug like the freeze plugs except 1/4”

On a freshly restored tri-power I had a a similar problem after opening the outboard carburetors.

I had to add a heavier duty torsion spring (from a 4bbl) on the rear carb so that the outboard carburetor butterflies would close completely. You need sufficient spring pressure to return all the butterflies to idle.

Mike told me I can tweak the lighter duty spring to get some more strength out of it too.

Confirmed that it's set-up correctly and turns clockwise, lowering the idle cam position.

I did the hand test to feel for any suction on the secondaries and did not feel anything, I did re-seal them with DAG about a year ago. I might have heavier duty springs to be extra sure though.

Idle vac is also about 17in/hg, which seems too good for a major vac leak. Maybe not?