High idle speed

[dbixby001]

I would like suggestions on why my engine might be idling very high. This just started.

I've had my Pinz for many years. I had the engine tuned about a year and a half ago. I've driven long distances in it and never had issues like this. I don't have a tach on it.

I recently drove for about 20 minutes on the highway. When I pulled off, the engine was still revving at a high speed as though I had the accelerator pressed. My first thought was that one of the springs was broken on the carburetor, but everything seemed normal and returned back to where it should be when the pedal was released. I let it sit for a few hours. I started it again and it immediately went to a high idle speed. About an hour later, I ran it again and it went to the high idle again, but then cycled to a normal rev and then cycled through highs and lows as though I was slowly giving it gas and then slowly releasing the pedal. I didn't see anything moving and there wasn't anything to mechanically affect the gas or air.

What is likely going on? What should I be looking at?

[pcolette]

Each Pinz owner has their own possible solution to this problem based on prior experiences. In my case I would first check your vacuum hoses, especially the main (long) one from the intake manifold to the brake booster. A worn spot, causing an air leak, would possibly give symptoms like you're seeing.
Best of luck!

[Hugues]

I had a similar behaviour when I adjusted my idle mixture valves way too low. Certainly you have not touched yours, but could one of them be clogged? Easy to check. And whole you are at it, make sure your starter lever on each carbs are closed.

[rmel]

Also check that your Carb's are tight to their base. On two occasions, one
on my 712 and then on a buddies 710 the bottom Carb screws worked loose
and resulted in a Vacuum leak.

There is also that dang balancing hose between the carbs that can leak over
time -- they get a ton of heat inside the air plenum.

[Stumbler]

Start with the simple, and cheap, and work your way to the more complicated and more expensive.

First, check the linkage. Is the spring properly placed? (If the throttle spring breaks, the truck will accelerate, but you have to pull the accelerator pedal up with your foot to make it idle. Any stiff joints or broken springs can cause variations on this.

Check that accelerator lock handle just below your seat. Make sure it is not pulled up, and be sure the choke is also off.

Check your timing and belts. Pull the distributor and check your points/electronic ignition/etc. Clean it out with a little spray and be sure it's as it should be. Set the timing. If you don't have one, get an old timing light. You can find new variations that digitally change the timing so you don't have to guess what 8 or 10 degrees are. You can set it and then match the marks exactly.

Check the settings on your carbs that nothing rattled loose or became maladjusted. Balance them,

If none of those are it, time to check vacuum hoses and wiring. Make sure everything is working as expected with no shorts are leaks.