[dlloyd]

I just installed my 1965 421 tripower in my 65 GTO. Butler bored and stroked it to 453&. mike Wasson restored the tripower unit for me.
When the motor gets to temperature I start hearing a squealing noise. I can’t figure out where it’s coming from. Any suggestion will lbe greatly appreciated.
Thanks David

[dlloyd]

Originally Posted by dlloyd

I just installed my 1965 421 tripower in my 65 GTO. Butler bored and stroked it to 453&. mike Wasson restored the tripower unit for me.
When the motor gets to temperature I start hearing a squealing noise. I can’t figure out where it’s coming from. Any suggestion will lbe greatly appreciated.
Thanks David

After rereading my post I want to correct it.
It’s not a squealing noise more like a whistle.
It don’t do it until the motor has warmed up.

[Dick Boneske]

My suspicion is that the noise is from the hot idle compensator, which is in the center carb. It is under a plate on the rear side of the center carb and has a little tab sticking out of it. Behind the plate is a thermostatically controlled valve that lets fresh air into the intake manifold only when the spring gets hot enough.

This hot idle compensator is used only on factory center carbs that were slated to be used with automatic transmissions. If your center carb has no plate on the backside, ignore all I said above, but that's my best guess as to where the whistle is coming from.

Another possibility would be a vacuum leak that only opens up when the engine gets hot. That could be in one of the carb base gaskets or the intake manifold-to-head gaskets.

It would be helpful to troubleshoot with a hollow tube such as a heater hose held to your ear while you move it to various spots on the top of the engine.

[dlloyd]

Originally Posted by Dick Boneske

My suspicion is that the noise is from the hot idle compensator, which is in the center carb. It is under a plate on the rear side of the center carb and has a little tab sticking out of it. Behind the plate is a thermostatically controlled valve that lets fresh air into the intake manifold only when the spring gets hot enough.

This hot idle compensator is used only on factory center carbs that were slated to be used with automatic transmissions. If your center carb has no plate on the backside, ignore all I said above, but that's my best guess as to where the whistle is coming from.

Another possibility would be a vacuum leak that only opens up when the engine gets hot. That could be in one of the carb base gaskets or the intake manifold-to-head gaskets.

It would be helpful to troubleshoot with a hollow tube such as a heater hose held to your ear while you move it to various spots on the top of the engine.

I bet you are right. My center carb does have the hot idle compensator.
That is a good tip about using heater hose to find the leak. I will give that a try this weekend.
If it is the hot idle compensator, what can be done to stop the whistle?! Is that normal? is there away to remove it or block it off?

[Old Man Taylor]

I took mine out and blocked it off.

[dlloyd]

Originally Posted by Old Man Taylor

I took mine out and blocked it off.

Can it be removed and blocked off without disassembling the carb?
What did you use to block it off?
Did your’s whistle before you removed it?

[Dick Boneske]

You could block it off without removing the carb, but not easily. It would be fairly easy to remove the carb, remove the sheet metal cover, and put JB weld into the vacuum passage.

[pfilean]

The manual says when setting idle to depress the hot idle (the little spring loaded button) to be sure it is not messing with the idle setting. If this whistle problem is just when hot then depress the button (again closing the hot idle compensator) and see if the whistle goes away. If it does go away the fix or block off the hot idle compensator. If the whistle stays look elsewhere.

[Dick Boneske]

Access to the hot idle unit on a ‘65 is not so easy. The sheet metal cover is between the center & rear carb. Removing it to gain access to the spring would be nearly impossible with the carb in place.

On the ‘66 center carb, you can reach the hot idle valve spring through the airhorn.

[Old Man Taylor]

Originally Posted by dlloyd

Can it be removed and blocked off without disassembling the carb?
What did you use to block it off?
Did your’s whistle before you removed it?

I did mine before I ever installed the carb, therefore it never whistled. It's been so long that I don't remember how I did it.

[dlloyd]

Update
Yesterday I pressed the hot idle compensator button and the whistling stopped. When I released it the whistling returned.
Looks like I have to block it with JB weld like Dick suggested. Thanks Dick!
I have another question. Does the hot idle compensator affect the idle rpm?
When I first start the car it idles at about 700 RPM. After I driving around it idles at 1000 RPM.
Is this normal or do I need to make an adjustment?

[Tom Vaught]

Yes, it affects the idle by bleeding more air into the intake manifold.

Tom V.

[dlloyd]

Originally Posted by Tom Vaught

Yes, it affects the idle by bleeding more air into the intake manifold.

Tom V.

Thanks Tom.
So blocking off the hot idle compensator should solve both my whistling and higher RPM issue.

[Tom Vaught]

Yes.

Tom V.