[Hotrodjohn71]

Hi group,
I have a 1965 Pontiac 326, bone stock, with a Rochester 2gc carburetor. The engine is freshly rebuilt and I rebuilt the carburetor myself.
The engine runs like a top except for one problem. When the engine is running the throttle body gets very tight. So tight that my strongest spring combination for the throttle return is barely enough to return it.
Or if it returns it to idle, it's too tight to press with your foot. This kind of throttle body assembly has no return spring built-in, but that shouldn't matter with the external throttle return spring set up.

*The thing about this is that when the engine is off, the throttle is very loose and easy to move. I took the carburetor off a little while ago and looked over the whole throttle body set up. There is no binding that I can see at all and it works perfectly easy when the engine is off.

Any ideas?

[Kenth]

Sounds like a swollen acc-pump cup binding in bore.

[steve25]

Please let me know if I have this straight, with the motor running and up to normal temp all you have to do is turn the motor off and the Carb is then fine?

[JSchmitz]

Check the throttle blades. Make sure that they aren't loose on the shaft. Also check your throttle shaft for wear in the base plate.

[dataway]

Sounds like vacuum is apply a force on something and causing it to bind. Maybe sucking in a bit of gasket that is interfering with the throttle plates?

[Pav8427]

Just read of a similar situation on a totally different carb over on HAMB that may or may not apply.
Seems a spring on one end of throttle shaft was putting a side load on throttle blades. When vacuum was applied, it caused blades to jamb and not return closed.
May be worth looking at.

[DANTIP]

I had this on a tri power center carb and Dick Boneske helped determine my throttle shaft was a tad tight. My carb was perfect when cold, but when warmed-up, the throttle would stick open a little. When it cooled down, it would return fully.

[Dick Boneske]

The most common cause of this issue is too little clearance between the throttle shaft and the cast iron throttle body. There needs to be at least .003" clearance, or the shaft will bind when the engine is hot. Too much clearance or wear causes idle problems, also, but sticking is usually due to too little clearance.

If you run a 8MM drill through the cast iron base, the .312" shaft will have about .003" clearance. The trick is--using a long drill, so you maintain alignment through all three holes in the base.

For troubleshooting, you may wish to disconnect the accelerator pump rod and drive the car. If the pump is sticking in its bore, this will cause a similar problem, but not likely only when hot.

[Hotrodjohn71]

Looks like I have rust.

[Dick Boneske]

I don’t think rust is the problem.

[Hotrodjohn71]

Hey fellas, I just wanted check in to put a period at the end of this thread. I got my issue solved.
I cleaned the throttle shaft with a 3m scotchbrite wheel and chucked up a bore cleaner into my drill and cleaned the throttle body housing and reassembled.
It works like new.
The symptoms were exactly like I described so I hope this thread helps someone else.
Your comments and advice made the difference.
Thank you.